Download Considering Fish and Fish Habitat in Existing Hydroelectric

Considering Fish and Fish Habitat in Existing
Hydroelectric Operations and Maintenance:
Electricity Industry Practices
Canadian Electricity Association
July 2001
CONTENTS
1.0 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Guiding Principles and Priorities . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Regulatory and Policy Framework . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Voluntary Environmental Management Initiatives . . . . . . . . . . . . . 8
2.0 OVERVIEW OF FACILITY OPERATIONS AND MAINTENANCE . . . . . 11
2.1 Components of a Hydroelectric Facility . . . . . . . . . . . . . . . . . . . 11
2.2 Operations Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.0 PRACTICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1 Reservoir Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.2 Flow Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2.1
Long-term Flow Management . . . . . . . . . . . . . . . . . . . . 30
3.2.2
Short-term Flow Management . . . . . . . . . . . . . . . . . . . . 35
3.2.3
Spillway Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.4
Synchronous Condensing Operations . . . . . . . . . . . . . . 44
3.3 Dams and Fish Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.1
Migratory Species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.2
Non-migratory Resident Species . . . . . . . . . . . . . . . . . . 50
3.4 Pumped Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5 Maintenance Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.5.1
Routine Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.5.2
Facility Repair and Rehabilitation Activities . . . . . . . . . . 57
APPENDIX A:
APPENDIX B:
APPENDIX C:
APPENDIX D:
Provincial Legislation and Regulations . . . .
Glossary (italicised words from text) . . . . .
Selected Readings . . . . . . . . . . . . . . . . . .
Instream Flow Assessment Methodologies .
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Note: Bolding of text throughout the report is used to emphasize key concepts
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Contents
1.0
INTRODUCTION
Canada’s hydroelectric generation has provided the principal technology for Canadian
power supply and a significant source of economic and social wellbeing for almost 100
years. In 1999, Hydro accounted for 61 percent of electricity produced nation-wide, with
much higher energy shares in Quebec, Manitoba, Newfoundland, and British Columbia
(see Figure 1.1). Hydroelectric power offers a secure, renewable, and flexible form of
generation that is a key component of the national and provincial generation mix,
complementing a rich endowment of fossil, nuclear, and alternative energy resources.
FIGURE 1.1
Canadian Electricity Generation
(GWh) Hydroelectric Share (%)
Yukon
T 318
H 87
O 13
B.C.
T 67,429
H 89
O 11
GENERATION
T: Total (GWh)
H: Hydroelectric (%)
C: Coal(%)
O: Other (%)
NFLD
T 44,946
H 97
O3
N.W.T.
T 695
H 37
O 63
Alberta
T 55,685
H4
C 78
O 18
Sask.
T 16,948
H 21
C 69
O 10
Manitoba
T 31,712
H 97
C3
Ontario
T 141,712
H 24
C 24
O 52
Quebec
T 154,734
H 96
C0
O4
P.E.I.
T3
O 100
N.B.
T 19,011
H 15
C 32
O 53
N.S.
T 10,757
H9
C 66
O 25
Source Electric Power in Canada , 1998-99 CEA Report
As we prepare to enter the next century, hydroelectric generation, like all other
power sources, is confronted by growing environmental, social, technological, and
economic pressures:
• Environmental issues – Existing hydroelectric facilities provide considerable
environmental benefits, most notably with respect to greenhouse gas and other
air emissions. However, there are also mounting concerns about the potential
negative effects of hydroelectric operations, in particular on fish and aquatic
habitat. In some regions of the country, federal and provincial regulators, First
Nations, environmental groups, and other stakeholders have been pressing for
greater protection and management of fish resources.
• Competing water uses – Over the years, hydroelectric operations have evolved
to balance the use of water for power production with other use requirements,
including flood control, recreation, fish and fish habitat, residential and
industrial water supply, and heritage and culture. As these competing
demands increase with population, urbanisation, and other socio-economic
pressures, hydroelectric producers face new and involved consultative
processes to better manage the various uses.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 1
• Technological development – Ongoing technological change in areas such as
computerised control systems and environmental technologies has helped to
maintain the competitiveness of hydroelectric power. At the same time, new
smaller-scale thermal generation technologies, including efficient gas turbines,
have emerged as a cost-effective alternative in many regions.
• Market restructuring – Driven by these new technologies and market change in
the United States and elsewhere, Canada’s electricity industry is undergoing
significant restructuring, albeit at different rates and to different degrees across
the country. The traditional monopoly notion of obligation to serve is giving
way to increased competition in supply. As one source of energy among many,
hydroelectric producers must now struggle to keep power prices low and
remain economically viable, while accommodating environmental and other
water use interests.
Of these priorities, the need to protect fish and aquatic habitat is an increasingly important
one, especially on Canada’s east and west coasts, where valuable migratory fisheries have
declined or disappeared. Some coastal ecosystems have been lost or degraded, while
others are now seriously threatened. In inland regions, as well, the conservation of
resident fish populations and their habitat is becoming an issue. Although many factors
have contributed to the call for increased fish and habitat protection, including overfishing
and forestry development, hydroelectric operations have also been a focus of concern for
regulators and stakeholder groups.
This is not to say that fish and aquatic habitat are new matters for Canadian hydroelectric
facilities. During the last two decades, environmental protection in general has become
an integral part of facility operations both in response to evolving regulatory requirements
and through voluntary actions initiated by electric utilities themselves. There is a need to
familiarise other producers, regulators, key stakeholder groups, and the general public
with respect to the industry’s ongoing efforts in this area.
Canada’s utilities view the current climate for fish protection as an opportunity to engage
all parties in a broad discussion of the effects of hydroelectric generation, and measures to
address those effects where they are harmful. Consequently, in November 1998 member
utilities of the Canadian Electricity Association (CEA) initiated a joint effort with Fisheries
and Oceans Canada (DFO) to document existing activities at Canadian hydroelectric
facilities for managing the fish-related impacts of operations. This document, Considering
Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance: Electricity
Industry Practices, represents the culmination of that cross-country effort.
For the purposes of discussion, a range of relevant hydroelectric operations and their
effects, both positive and negative are considered herein. In fact, the operation of
hydroelectric facilities varies from one region to the next and from one site to another
within a given region, depending on climate, topography, hydrology, electricity needs,
and other factors. These differences in facility operations, as well as the nature of the
species and stocks in question, make for varying impacts on fish and fish habitat. As a
result, not all of the fish practices outlined below are common to all Canadian producers.
Generally, this document describes a spectrum of practices and, where possible, notes
particular cases (e.g., regions) of, as well as exceptions to, their application.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Given such regional variation, this document is not intended as a prescriptive “code of
practice” to instruct hydroelectric producers on how they should undertake fish and
habitat protection. Rather, its purpose is to provide an illustration of fish-related impacts
and practices at Canadian facilities. The document aims to provide information on the
nature of hydroelectric operations and ongoing efforts to balance the multiple interests
and requirements regarding water use. As such, it should be useful to hydroelectric
producers, government, stakeholders, and the public in general.
The document begins with a description of the regulatory and policy framework for
hydroelectric operations and the industry’s voluntary environmental initiatives. Then,
Section 2 provides background on the components of a hydroelectric facility and the
process of operations planning to balance power production and other water uses.
Finally, Section 3 contains the detailed explanation of individual hydroelectric operations,
their fish and fish habitat effects, and existing practices. Supporting information, including
definitions of terms and selected references, are presented in appendices.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 3
1.1
GUIDING PRINCIPLES AND PRIORITIES
At the end of the 20th century, Canada’s electricity industry is striving to maintain a
standard of excellent value and service in an increasingly complex economic and social
environment. For the hydroelectric portion of the industry, the challenge will be to
continue deriving benefits from our endowment of relatively low-cost water resources
using sustainable management practices that address public concerns about fish
protection and other water use priorities.
From a broad perspective, the industry’s operating principles reflect a commitment to
sound management practices, just like any other business. Canadian hydroelectric
producers operate their facilities to balance a number of priorities:
• Safety and reliability – Facilities must be operated to ensure a continuous,
uninterrupted flow of power to customers. Safety refers not only to reliable
electricity supply, but also to a host of other matters, including dam safety,
flood control, emergency communications, and security of the entire
power system.
• Economic viability – Operations must be conducted in a manner that controls
system cost and maintains cost-competitiveness with potentially competing
energy sources (e.g., natural gas). As electricity markets open up and prices
become more market-driven, the continuing financial viability of generation
will become a more pressing issue.
• Environment – Producers must operate their facilities to minimise negative
impacts on the environment, including fish and aquatic habitat. The first
priority is to avoid harmful impacts to the fullest extent possible. Where these
impacts cannot be avoided, mitigation and compensation measures are then
explored and implemented, if feasible, to address them.
• Social welfare – A key legacy of the power industry is its role in fostering
economic development and industrialisation in Canada. While this role may
evolve in a more competitive market, producers must continue to respect the
needs and desires of local communities, First Nations, industry, other interest
groups, and the public at large.
The balancing of these priorities is achieved in part through the prevailing regulatory and
policy frameworks within which hydroelectric producers operate. In addition, the industry
goes a step further by undertaking voluntary initiatives to protect the environment and
further social welfare. The practices described in this document reflect both these
regulatory and policy requirements and voluntary efforts by producers.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
1.2
REGULATORY AND POLICY FRAMEWORK
Most hydroelectric generation facilities across Canada are authorised under provincial
licenses, leases, and water rights. Under the Constitution Act, the federal and provincial
governments have their own exclusive spheres of legislative responsibility. The provinces
have ownership of natural resources and legislative authority over the management and
sale of provincial public lands and civil rights. While provincial jurisdiction encompasses
navigable waters (except those on federal Crown lands) and the fish contained therein, the
federal government is empowered to enact laws respecting navigation and fisheries.
A range of policy and legal devices established by these agencies governs the operation of
hydroelectric facilities. Canadian producers adhere to contractual agreements and
obligations established through boards, agencies, and treaties, as well as to the principles
of common law.
The major federal and provincial legislation and policy relevant to hydroelectric
operations are outlined below. The legislation included below, and the outline provided,
are not exhaustive, and the reader is encouraged to contact the administrative agency
directly for more detailed interpretation and understanding about the application of the
referenced legislation.
Federal Legislation and Policy
The Fisheries Act is the principal federal statute with respect to fisheries in Canada. It
applies to waters in the fishing zones and territorial seas of Canada, and to inland waters.
Administered by DFO, the Act is intended to protect and manage fisheries, fish, and their
habitat. It provides a framework for the conservation, restoration, and development of fish
habitat, as well as strategies for the implementation of programs and initiatives. Given the
scope of the Fisheries Act, there are many situations where hydroelectric facilities,
operations or activities are potentially covered by the Act. For example, there are specific
provisions concerning the harmful alteration of, disruption or destruction of fish habitat,
maintenance of fish screens, construction and operation of fishways, and the provision of
flows below obstructions. Due to the complexity of the Act, and the range of
hydroelectric facilities, activities and operations that may be covered, utilities work closely
with DFO to understand the applicable legal requirements.
To assist in the administration and use of the Fisheries Act, Fisheries and Oceans Canada
adopted a Policy for the Management of Fish Habitat, in 1986. The policy outlines
DFO's objectives, goals, and strategies for the management of fish habitat supporting
Canada's freshwater and marine fisheries. Its long-term objective is an overall net gain in
the productive capacity of fish habitats. The "no net loss" principle is to be applied
prospectively to proposed projects and undertakings, but not retroactively to approved or
completed projects. Under this principle, DFO will strive to balance unavoidable habitat
losses with new projects with habitat replacement on a project-by-project basis, in order
to avoid reductions in fisheries resources due to habitat loss or damage. The policy is
considered a blueprint for a practical, co-operative approach between the private sector
(including hydroelectric utilities) and various levels of government.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 5
The Canadian Environmental Assessment Act (CEAA) is potentially pertinent to fish and
fish habitat, since it requires an environmental assessment for new projects or activities
meeting certain criteria. Sustainable development is established as a fundamental
objective of the federal environmental assessment process. CEAA may also be triggered
by the Fisheries Act under some circumstances. Maintenance activities, however, are
exempt under the Act.
The federal government has drafted endangered species legislation that was tabled in the
House of Commons in February 2001. This follows on a 1996 commitment by the
federal, provincial, and territorial governments to establish complementary legislation and
programs that provide for the effective protection of species at risk across Canada. The
Species at Risk legislation may become an important issue for hydroelectric facilities, as
operations can interact with endangered species and their habitat.
Hydroelectric generation facilities may also be affected by the Canadian Environmental
Protection Act. This legislation provides a framework for the life cycle management of
toxic substances from development and manufacturing through to use, storage, and
disposal. Maintenance and, to a lesser degree, operational practices may be influenced
by the Act.
Other federal legislation and agreements that may apply in certain circumstances include:
•
•
•
•
•
•
•
•
•
Page 6
Navigable Waters Protection Act
Transportation of Dangerous Goods Act
Migratory Birds Convention Act
The Indian Act
The Explosives Act
The Canada Water Act
The Canada Wildlife Act
The International River Improvements Act
International Boundary Waters Treaty (1909).
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Provincial Legislation
The provinces have jurisdiction over water utilisation, including hydroelectric
development, within their boundaries. In most provinces, hydroelectric facilities are
licensed or authorised under provincial legislation. Typically, the licenses or
authorisations set out operating parameters that may include environmental provisions,
such as riparian flows. The degree to which environmental considerations are included in
licenses is usually related to the date of licensing and the level of environmental
awareness at that time. Relicensing, on expiration of the original license, is often an
opportunity to reassess the environmental impacts and incorporate environmental
provisions into the operating parameters. Plants built after the enactment of federal and
provincial environmental assessment legislation will have compliance with environmental
approval conditions as a condition of the water license.
There is an array of provincial legislation concerning environmental protection and
management that is relevant to the day-to-day operation of hydroelectric facilities.
Appendix A lists the major pieces of legislation for each province and territory, and
demonstrates the range and scope of the requirements under which facilities are
operating.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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1.3
VOLUNTARY ENVIRONMENTAL MANAGEMENT
INITIATIVES
Together and individually, Canadian electricity producers have developed a number of
voluntary programs and practices to manage the environmental impacts of their
operations. Examples of two major industry-wide efforts are provided below.
Environmental Commitment and Responsibility Program
In November 1997, the CEA launched the Environmental Commitment and Responsibility
(ECR) Program to help co-ordinate environmental management activities by member
utilities. Under ECR, producers commit to operate their facilities according to four
basic principles:
•
•
•
•
be more efficient in the use of resources
reduce the adverse environmental impact of business
be accountable to constituents
ensure that employees understand the environmental implications of their
actions, and have the knowledge and skills to make the right decisions.
Each utility must track its environmental performance with respect to these principles,
using a series of common indicators. In addition, each must implement an Environmental
Management System (EMS) consistent with ISO 14001 standards. These standards refer to
the most recent EMS requirements developed by some 70 countries through the
International Standards Organisation.
The practices described in Section 3 reflect the spirit of the ECR commitments made by
Canadian utilities. They can assist hydroelectric producers in meeting environmental
requirements by identifying the variety of operational effects and other considerations for
effective water management. The practices outline specific activities to help producers
address the negative effects of their operations. In addition, they provide information for
tracking environmental performance and meeting other 1S0 14001 specifications for an
environmental management system.
Environmental Management Systems (EMS)
The ECR program requires that individual utilities implement an EMS consistent with the
document, ISO 14001-96: Environmental Management Systems – Specification with
Guidance for Use.1 This is the first in a series of documents related to the implementation
and maintenance of environmental management systems.
At the heart of the ISO 14001 Specification are 18 “elements” that must be in place to
ensure an effective environmental management system. Critical requirements are to:
• have an environmental policy appropriate to the nature of the organisation
• identify significant environmental aspects of the organisation’s activities,
products, and services
1 Canadian Standards Association (1996).
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
• establish objectives and targets for significant environmental aspects, including
pollution prevention
• ensure that management programs exist, with supporting resources and
appropriate training of relevant personnel, to move towards those objectives
and targets
• improve continually on the EMS.
The information on practices in Section 3 can be useful for hydroelectric producers in
identifying fish and fish habitat issues associated with their operations. It can also
contribute to the development of objectives, targets, and related management programs
consistent with the ISO 14001 Specification.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 9
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
2.O OVERVIEW OF FACILITY OPERATIONS AND
MAINTENANCE
This background section provides an overview of the hydroelectric operations, with a
basic description of how facilities work and the process of operations planning.
SPILLWAY GATES
HEADPOND
SPILLWAY
DAM
TAILRACE
TRANSFORMER
POWERHOUSE
RIVER
FIGURE 2.1
View of a Hydroelectric Generation Station and Associated Facilities
2.1
COMPONENTS OF A HYDROELECTRIC FACILITY
Hydroelectricity is produced by an extensive and complex system designed to harness the
kinetic energy of flowing water (see Figure 2.1). This energy is captured and controlled by
dams and carried through pipelines (penstocks) to turbines. Water flowing through the
turbines causes them to rotate, which in turn drives the generator. The generator then
converts the mechanical energy into electric energy for transformation and delivery to
consumers through a network of high voltage transmission lines and lower voltage
distribution lines.
The principal components and operations of a hydroelectric facility are described below.2
2 Italicized items are defined in appendix B.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 11
Dam
The foundation of a hydroelectric power facility is the dam: an earth-filled and/or concrete
structure that retains the reservoir. Dams control the flow of water and increase the
elevation to create head (the difference between upstream and downstream water levels)
so that energy can be produced. They can be equipped with a variety of water release
structures, including turbines for electricity generation, spillway gates to control flooding,
and other gates and ports that can be used for non-power-related purposes.
Dams can serve any combination of storage, diversion, or power generation needs.
Often, they are described as being either storage or run-of-river, although the distinction
between the two is not absolute. Storage dams are designed to store large volumes of
water in reservoirs until required for electricity generation, with water levels typically
fluctuating as a result. While most dams are built in the main river channels, some are
utilised as side dams to cover low points in topography.
In contrast, run-of-river dams, some of which are known as head pond dams, do not store
significant amounts of water in a reservoir, but rather let the water flow immediately past
the dam. In this case, the ability to produce power depends on the head, surrounding
topography, installed generating capacity, and the volume of water flow.
Powerhouse and Plant
The powerhouse contains the turbines, generators, and related equipment that are used to
convert the energy stored in water into electricity. Powerhouses can be standalone
buildings connected to the reservoir through an intake and penstock, or they can be an
integral part of the dam holding back the reservoir. (See Figure 2.2)
The difference between the forebay water level (immediately upstream of a generating
station) and the tailrace water level (immediately downstream of the station) defines the
hydraulic head. Typically, hydroelectric power plants are designed for ranges of head and
water discharge volume. The powerhouse in a run-of-river operation can often be much
smaller, since the unit has been sized to operate with the available base flow in the river.
On the other hand, a plant that has access to significant storage will tend to be larger,
because it has been sized to pass more water during shorter time periods in order to meet
system energy demand.
The type of turbine used for generation is also dependent on the size of facility (i.e., head)
and operating mode. Currently, Francis and Kaplan turbines are the two predominant
types found in Canadian hydroelectric facilities.
Some conventional hydroelectric power plants, such as run-of-river facilities, operate
continuously to provide base load energy to the system (base load plants). Peaking plants
run only for limited periods of time when there is additional demand for energy (peak
load). Pumped storage facilities, which are very rare in Canada, pump water back up into
the reservoir during off-peak periods for later peaking use.
Inherently, the dam, powerhouse and plant tend to be large, fixed structures, designed to
withstand the very significant forces associated with stored or moving water. This means
that it is inherently difficult to make retroactive modifications to the main facilities for any
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
reason. However, modifications may be periodically required at some facilities, and this
may, under some circumstances, provide opportunities to address environmental concerns.
Hoist
Headwater
Elevation
Penstock
POWERHOUSE
Transformer
Crane
Headworks
Turbine
Generator
Tailwater
Elevation
Draft
Tube
FIGURE 2.2
Cross-Section of a Typical Hydroelectric Generating Facility
Reservoirs
The portion of a hydroelectric facility that is farthest upstream is the reservoir: the body of
water behind the dam. Storage reservoirs are similar to rechargeable batteries, storing
potential energy in the form of water that can be replenished by runoff water from rain
and melted snow. Inflows, evaporation, and the dam operations therefore control the
water level in a reservoir.
Climate, topography, and season influence the rate at which reservoirs fill. In general,
reservoirs in the west fill during the spring and summer, while those in the east do so in
the spring and fall. Most are drawn down during the winter when the demand for
electricity increases. The rate and extent to which this filling and drawing down of the
reservoir occurs varies across the country.
Storage refers to the total volume of water upstream of a generating station or dam at any
particular point in time. Storage capacity is the amount of water contained between the
reservoir’s maximum and minimum allowable levels, while live storage is the amount
available for power generation or other purposes. In most instances, live storage is less
than the capacity level due to physical or regulatory constraints. Reservoir storage
volumes and ranges in forebay elevation are defined by the topography of the site.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 13
In addition to their power production uses, reservoirs potentially provide a number of
other benefits, including recreation, commercial transportation, commercial fishing, and
property development. For example, there are agreements in place governing the
management of water elevations in a number of headwater reservoirs in New Brunswick.
These agreements were established with the intent of maintaining and protecting the
recreational fisheries potential in those lakes.
Diversion
A diversion is a partial or total redirection of a water flow from one river or watershed into
another in order to increase flow, head, and/or hydroelectric power production.
Diversions are designed and operated to provide optimal flows to the intake canal or
receiving watershed, or minimum flows to the river downstream of the diversion point.
During a flood, excess flow may be returned to the river downstream of the diversion
point.
Downstream Flows
Aside from head, a key consideration for hydroelectric generating capability is the flow of
the river below the dam. The volume of this downstream flow is determined by the
amount of water passing through the turbine(s) or other release facilities. Most dams
change the natural flow regime of the river. Although the same amount of water enters
the regulated river (after dam construction) as occurred in the unregulated (pre-dam)
system, the operation of the dam can affect when, where, and how quickly water is
released downstream.
At some dams, all of the water is returned to the river, but at a different time and rate than
before the dam was built. At run-of-river operations, water is discharged or released at
essentially the same volume and time as it enters upstream. Diversion facilities, on the
other hand, may alter the downstream flow by diverting water from one river system to
another to increase flow for power generation. When heavy rains fall for a long time
and/or during periods of high snowmelt, reservoirs begin to fill up as more water collects
than is released. During these periods, the excess water may be released past the dam
through a bypass flow (the spillway).
Cascading Systems
In a cascading system, hydroelectric facilities are located sequentially along the same
watercourse, where the outflow from one facility flows directly into the reservoir of the
next (see example in Figure 2.3). In general terms, a cascading hydroelectric system is
developed to take advantage of the natural slope of the riverbed (i.e., elevation drop)
along the river course. The size of storage and magnitude of flows determine how much
the water levels may fluctuate.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
460
260
ARNPRIOR
ARNPRIOR
OTTAWA
OTTAWA
A RIVER
RIVER
201.17
300
STEWARTVILLE
STEW
TVILLE GS
STEWARTVILLE
GS
246.41
340
CALABOGIE
ALABOGIE CHUTE
CALABOGIE
CHUTEGSGS
283.46
380
150.92
144.78
99.06
220
180
ELEVATION IN METRES
MOUNTAIN
MOUNT
AIN CHUTE
MOUNTAIN
CHUTEGSGS
420
BARRETT
ARRETT CHUTE
CHUTE GS
BARRETT
GS
GRIFFITH
GRIFFITH
D DAM
KAMANISKEG
LAKE
KAMANISKEG
LAKE
DAM
313.94
Generating Stations and Storage Dams on the Madawaska River
BARK
ARK LAKE
LAKE D
DAM
BARK
DAM
D
ROCK LAKE DAM
988.01
GALEAIRY LAKE
GALEAIRY
GALEAIRY
LAKEDAM
DDAM
LAKE OF TWO
O RIVER DAM
DAM
392.89
390.75
LONG
LONG RAPIDS
RAPIDS
FIGURE 2.3
140
100
74.22
60
250
200
150
100
DISTANCE IN km FROM THE OTTAWA RIVER AT ARNPRIOR
50
0
LEGEND
EXISTING STORAGE DAM
EXISTING GENERATING STATION
153.92
2.2
RESERVOIR ELEVATION (m)
OPERATIONS PLANNING
The planning of hydroelectric operations involves a complex balancing act to co-ordinate
power production, energy requirements, and other key uses of the water resource.
Operations’ planning is the decision-making process undertaken by producers to provide
safe, reliable, and cost-effective electricity service, while accommodating these other use
requirements as much as possible.
Hydroelectric producers plan their operations to account for varying customer demands
and water inflows over time – variables that are essentially outside their control. The
hydroelectric system must be operated in conjunction with other generation sources to
ensure consistent power supply, and must recognise the interactive effects between river
basins within the system itself.
Operations planning involves the preparation of energy forecasts, capacity commitments,
and power dispatch, all within a framework of regulatory and voluntary constraints. As
such, it must draw on a variety of detailed information, including water supply (and
weather) forecasts, market forecasts, historical databases describing the past performance
of the facility and system, and real-time databases describing the existing system to
determine the optimum schedule for power generation.
Although specific details vary across utilities, planning typically begins with a long-term
(e.g., 24-month or longer) hydroelectric energy forecast that is integrated with other
generation sources into a production plan. At this point, strategies are developed to
deal with energy shortages and surpluses, energy and capacity purchases, and other
factors to produce a monthly forecast. Multi-week capacity estimates, station maintenance
outages, and capacity problems are then added to develop a weekly capacity
commitment. Finally, a 24-hour megawatt generation profile is produced for the entire
bulk power system.
Regulatory, environmental, and social constraints are incorporated into operations
planning through operating limits on reservoir and flow management. These practices are
discussed in Sections 3.1 and 3.2, respectively. The remainder of this section outlines
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 15
power and non-power issues that are considered in hydroelectric operations, as well as
new water management planning processes being used to balance those issues.
Hydroelectric Power Production
Hydroelectric operations are designed to match energy generation to electricity demand
on an instantaneous, hourly, daily, seasonal, annual, and in some cases multi-year basis.
Demand varies with customer requirements over time, while hydroelectric generation
potential varies with seasonal weather conditions and water inflows. In Canada,
electricity requirements tend to be highest in the winter (although summer demand is ever
increasing), when inflows are at their lowest level. Demand is also higher during
weekdays and lower at night and on weekends.
Hydroelectric producers plan their operations to meet average energy demand over a
period of time (the base load), as well as peak demand. In addition to covering customer
requirements, the producer must reserve sufficient power to allow for demand forecast
errors, unscheduled outages of generating units, normal system dynamics, and extreme
weather events. Some operators plan on the basis of having sufficient energy (i.e., in
water storage) to accommodate a record low inflow over a certain period.
During years when inflows are higher than average, producers with large storage reservoirs
refill their reservoirs and attempt to sell any surplus energy (in excess of storage capacity)
to avoid spilling. When inflows are below average, they draw down the reservoir, use
other generation sources to supplement the hydroelectric system, and purchase electricity
from other producers. Reservoir levels are carefully controlled to balance current and
future electricity requirements, the risk of spilling, and other water uses (e.g., flood
control).
Power System Security
Hydroelectric producers have a responsibility to provide safe, reliable electricity service to
their customers. At the direction of provincial energy authorities, they may be relieved
from meeting environmental constraints in order to deal with temporary shortages or
excesses of energy. This may be done to:
•
•
•
•
match electricity generation to demand
maintain the frequency/voltage quality
ensure sufficient operating reserve for generation loss protection
prevent load cuts where parts of the electrical grid are not supplied with power.
In some areas, the authority to address energy emergencies resides with the electric
utilities. In others, an independent market operator (i.e., in Ontario and Alberta) will
handle such emergencies on behalf of the province. In addition, the fact that all utilities
are interconnected with neighbouring utilities allows some of the energy emergencies to
be managed on a regional basis.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Facility Maintenance
Like other industrial facilities, hydroelectric power plants must plan for ongoing
maintenance to ensure their continued safe, efficient, and reliable operation. A significant
portion of this ongoing maintenance involves predictable activities conducted in
accordance with well-established guidelines, codes, or legislation. Typically, the activities
occur on a regular (monthly, annual) cycle and are part of the scheduled facility
operations. Examples include mechanical maintenance of equipment, the upkeep of
exposed structures (e.g., surface concrete work, and painting), and property maintenance
around the dam and headponds.
Another class of maintenance activities relates to significant facility repairs and rehabilitation.
In this case, the work is not part of an ongoing maintenance program, but rather is a unique
activity to address a single problem. For example, facility repairs may be required to replace
an unsafe spillway structure or an eroded draft tube. These activities often require specific
approvals or permits, and involve considerable planning and co-ordination with stakeholders
and regulatory authorities.
Regular maintenance activities that occur outside the powerhouse tend to involve the
public or key stakeholders. The reason is that they are usually undertaken to address
property owner concerns, or the work has some impact on other users of the waterway
(e.g., recreational or commercial boaters). The impacts of both kinds of maintenance
activities on fish, fish habitat, and other water uses are discussed in Section 3.5.
Flood Management
In river systems where flooding threatens public safety, property, or facility integrity, flood
management will likely be given priority over hydroelectric generation and other water
uses during certain times of the year. Hydroelectric producers may assist in flood
management together with regional, provincial, interprovincial, and international
authorities, as appropriate (e.g., Lake Superior Board of Control, Lake of the Woods
Control Board, Columbia River Treaty). In most cases, planning and operations for flood
control are dictated to the producer by the agency or agencies involved.
Examples of Water Use Trade-offs
• Flood control favours the late filling of
reservoirs (to reduce the risk of a late spring
flood), while early filling helps spring
spawning and stranding of fish.
• Flood control reduces the natural flooding
cycle required for floodplain wetland or
delta ecosystems, affecting vegetation and
wildlife.
• The management of river currents to
facilitate navigation may disturb fish
migration routes.
Drawing down the reservoir, which
increases storage capacity, creates the
capability for flood control.
Alternatively, a special allowance for
flood storage may be created above the
normal maximum (full supply) limit for
reservoir operations. In Canada,
hydroelectric reservoirs are especially
useful in managing the spring freshet
since demand is high in the winter and
reservoirs usually reach their minimum
elevation just before it. If reservoir
filling coincides with the peak of the
freshet, downstream spills can be
moderated, controlling river flows.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 17
During moderate freshets, this activity may be sufficient to reduce or even eliminate
flooding, but in extreme years hydroelectric operations will likely have no significant
effect on this natural phenomenon.
Storage reservoirs are managed to minimise spilling water because of the loss of potential
revenue. However, in anticipation of or during a flood event, the operator may be forced
to spill to ensure dam safety or protect property on the reservoir, and to comply with
licence obligations. Spilling commonly occurs at Canadian hydroelectric facilities during
the spring and, occasionally, at other times of the year. Section 3.2.3 on Spillway
Operations describes the effects and practices associated with these spills.
Water Supply and Effluent Dilution
Water supply for residences, agriculture, and other industry is another important
consideration for hydroelectric producers. Water intakes are usually constructed in the
deepest parts of reservoirs and rivers. In some cases, however, there may be a risk of
dewatering these intakes during droughts. Producers may attempt to provide minimum
flows at certain times of the year to keep intakes covered.
At the request of regulatory agencies, reservoir operators may provide minimum daily
releases for some rivers to provide dilution for downstream sewage treatment plants or
industrial facilities. The most common reason for doing so is to prevent anoxia (oxygendeprivation) or to protect fish from toxic chemicals. Even when not specifically requested,
rivers with storage reservoirs in the headwaters usually have higher flows and dilution
rates during naturally low-flow periods in the winter and late summer.
Ice Management
In cold climates, the natural formation of ice on rivers and lakes can cause flooding (e.g.,
when ice jams are created or released), block intakes to domestic or industrial water
supplies, and reduce hydroelectric generation through intake blockage, reduced river
conveyance, and elevated tailwater levels. Ice can also impact fish habitat through
changes in water flows (velocities), flooding, scouring of riverbeds and banks, and the
transport of sediments. Generally, the extent and duration of these ice impacts depends
on a number of factors, including water and air temperature, river characteristics, flow
rate, and pre-existing ice conditions.
Although ice-related issues arise with or without hydroelectric operations, these facilities
can influence ice formation, particularly in areas near water control structures.
Depending on the forebay elevation, upstream ice conditions can be more or less stable
than in the unregulated river. At key times of the year, changing water flows from
operations may also affect downstream ice stability.
Hydroelectric producers practice ice management primarily to attempt to maximise river
conveyance by limiting ice restrictions, and control damage and flooding by reducing the
severity of ice jams and runs. During freeze-up, they can regulate flows and water levels,
or operate ice control structures (e.g., ice booms, weirs), to establish stable ice covers in
critical areas. Periodic spills can increase flows or draw from deeper zones of reservoirs
(for a modest increase in downstream river temperature) to reduce the production of
Page 18
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
subsurface ice. During break-up, ice control structures can be operated and flows
regulated to limit the damage from flooding.
Navigation
Hydroelectric stations have been developed on a number of Canadian rivers that
are mainly dedicated to water transportation of goods and raw materials (e.g., the
St. Lawrence Seaway, Mackenzie River, St. Mary’s River, Fraser River). For these
waterways, flows and water levels are controlled by the relevant federal or international
agencies responsible for navigation (e.g., Fisheries and Oceans Canada, St. Lawrence
Seaway Authority, International Joint Commission’s Boards of Control).
In such systems, the dams were built at the base of rapids to create headponds to facilitate
navigation. Navigation locks or boatlifts were then constructed around the dams.
Hydroelectric stations were often added to take advantage of the head for power generation.
Operationally, water levels are maintained to prevent the grounding of boats. The lock
systems get first priority for flows, although these may not be significant for hydroelectric
operations. Hydroelectric discharges may be controlled to prevent interference with boat
movements. Water levels may be lowered in the winter to prevent damage to locks and
other structures.
Recreation
Rivers and reservoirs that are used for hydroelectric generation are often key recreational
resources, especially since many Canadian reservoirs are simply minor expansions of
former lakes. Summer recreational uses (e.g., cottages, camping, boating, angling,
swimming) are prevalent, although winter uses (e.g., snowmobiling, ice fishing) are on the
rise. Many producers have voluntarily constrained their summer operations to facilitate
recreational activities, despite reduced operating flexibility and rising summer power
demands in some provinces.
Typically, recreationists prefer
operations that provide relatively
constant reservoir levels during the
summer months for boating and
shoreline structures (especially docks
and beaches). Downstream, they
prefer constant and moderate flows.
For hydroelectric generation, these
preferences tend to conflict with
summer drawdowns and peaking and
ponding (filling) operations. However,
the preference for moderately high
levels in headponds and forebays does
harmonise with the producer’s desire
to maximise head.
Examples of Complementary Water Uses
• Hydroelectric peaking operations that
maximise downstream flows during the day
can facilitate canoeing, kayaking, and rafting.
• Higher reservoir levels for summer recreation
also maximise habitat for fish in shallow
waters and summer spawners.
• Minimum reservoir releases to keep water
supply intakes covered protect spawning
habitat and reduce the risk of fish being
stranded.
• Creating a stable ice cover over a headpond
allows more winter recreation use (e.g.,
snowmobiling, ice fishing), while optimising
flow conditions for the producer.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 19
Peaking operations that maximise downstream flows during the day may facilitate
kayaking, canoeing, and rafting. River flows may also be constrained to facilitate angling.
Heritage
In many parts of Canada, hydroelectric reservoirs and facilities may be located in close
proximity to sites with heritage value. Canadian river basins were historically used as
navigation routes and settlements were often located on river floodplains. The creation of
reservoirs that flood river bottoms and the alteration of river discharges can influence
access to and stability of heritage sites. There are a variety of heritage values that may
apply to reservoir operations, including First Nations cultural sites, European settlement
locations, and more recent social and industrial sites.
Operational impacts of hydroelectric facilities on heritage sites result from flooding,
restriction of access, erosion processes due to reservoir operations and water releases, and
the disruption of heritage uses of some key locations for settlement, hunting, and fishing
activities. Where possible, consideration of these values, as well as present access and
use of sites, are taken into account in operations decision-making.
Wildlife
Wildlife that depend on habitat in rivers and reservoirs influenced by hydroelectric
operations must also be considered when making operating decisions. Migratory bird
nesting, aquatic mammal overwintering and ungulate use of riparian habitat for calving
and feeding are examples of the types of habitat requirements by wildlife. In some
situations, wildlife use will be inconsistent with preferred use for power generation or
other resource objectives.
Riparian zones (the terrestrial areas along the edge of water bodies) are among the most
productive and diverse types of wildlife habitat. The fluctuating water levels from
hydroelectric operations, in particular severe winter drawdowns of the reservoir, can
significantly alter riparian habitat and impact the wildlife that relies on it. Floodplain
wetlands or river deltas, with their extensive riparian zones, are especially sensitive to
these fluctuations, since they depend on seasonal water flows (e.g., spring flooding) for the
maintenance of their ecosystems.
Fish and Fish Habitat
Federal and provincial environmental assessments for new hydroelectric projects now
ensure that constraints are applied to new hydroelectric operations to protect fish and
aquatic habitat. At some existing facilities, producers have voluntarily initiated reviews of
their operations to identify flow and water level effects on other uses, including those
related to fish. If feasible, operational changes may be made to protect or enhance fish
and their habitat. If such changes are not feasible, other measures may be undertaken to
mitigate or compensate for the negative effects of operations. Specific practices for fish
protection at Canadian hydroelectric facilities are discussed in Section 3.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Water Management Planning Processes
The manner in which hydroelectric producers plan the operation of their systems, and
seek and incorporate public input into that operation, varies considerably across the
country. More and more, the need to balance electricity production with other water uses
in the watershed requires co-operative partnerships with regulatory agencies, local
communities, and resource users. These partnerships are increasingly referred to as
“water management planning processes.”
Water management planning is being adapted on a regional basis to reflect differences in
regulatory processes, river systems, hydroelectric operations, fishery and other resource
use priorities, and stakeholders’ interests and partnering opportunities. The objective of
the planning process is to establish a set of operating rules for individual facilities, or
groups of facilities, that outline limits and targets for water level and flow. Although
consensus on the operating rules may not be achieved in every case, the decision-making
process recognises trade-offs among water uses.
Examples of current planning processes include:
• British Columbia’s Water Use Planning process is a formalised and legislative
approach to water management. Water use planning guidelines have been
developed under the province’s Water Act to enhance water management at
hydroelectric power and other water control facilities. The purpose of these
guidelines is to instruct licensees and proponents on the preparation and
approval procedures for Water Use Plans, and to inform key stakeholders on
how to participate in plan development. The concept is based on a consensus
approach to decision-making that involves agencies, First Nations, and key
interested parties.
• The Operating Approval Renewal Process is a formal program used in Nova
Scotia to review station operation and environmental conditions in
hydroelectric watersheds. It was developed jointly by the provincial
Department of the Environment and Nova Scotia Power Inc. The process
involves consultation with regulatory authorities and the public to identify
issues and concerns, and to better accommodate the needs of other water
users through incremental improvements to operations.
• Ontario’s Water Management Planning Process forms the foundation of a new
business relationship approach to water management planning advocated by
the provincial Ministry of Natural Resources and hydroelectric producers. The
focus is on how water levels and flows affect aquatic ecosystems and other
resource uses. The objective of the planning process is to develop and
communicate publicly a water management plan for the river system. The
review process involves an assessment of the existing water management
regime from an ecosystem, watershed, and resource perspective; public
involvement; and the completion of an interagency plan for improved
management. To date, only one such plan has been developed, but three more
have been initiated, with further planning exercises to come.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 21
• Following on a 1996 commitment to the principle of watershed management,
Quebec is involved in a pilot project on the Chaudière River. In 2000, an
implementation committee presented a report to the Minister of Environment
on the content of a water management plan for the system. In addition, the
provincial Public Hearing Board on the Environment presented its’ report,
following public consultations, to help develop a formal water management
policy. The policy will cover surface and underground water, as well as
hydroelectric generation and the exportation of bottled water.
• In addition to formal processes, hydroelectric utilities conduct ongoing
external communications and consultations to identify and resolve water
management concerns as regulators, stakeholders, and the general public raise
them. Many producers have developed innovative means to communicate with
other users of the river system. These include websites, hotline telephone
numbers, newsletters, regular items in news media, and town hall meetings.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.0
PRACTICES
This section outlines a series of issues related to the operation and maintenance of
hydroelectric facilities, their effects on fish and fish habitat, and current practices to
address these effects. The following operational issues are examined:
• Reservoir Management
• Flow Management
♦ Long-term Flow Management
♦ Short-term Flow Management
♦ Spillway Operations
♦ Synchronous Condensing Operations
• Dams and Fish Movement
• Pumped Storage
• Maintenance
♦ Routine Maintenance
♦ Facilities Repair and Rehabilitation Activities
In each case, a Description of the operational issue is provided, followed by an outline
of the Fish and Fish Habitat Effects from the operation. Next, important Other Considerations
(e.g., facility design and configuration, water characteristics, other water use requirements)
that potentially constrain facility operations and fish practices are identified. Finally, existing
Practices are listed, categorised under Operations, Mitigation, and Compensation. Examples
of applications of the practices in individual provinces are also highlighted in a sidebar.
Selected references on each of the topic areas above are presented in Appendix C.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 23
3.1
RESERVOIR MANAGEMENT
Description
Storage reservoirs provide the necessary water to meet electricity needs at any point
throughout the annual hydrological cycle. Seasonal storage creates head and allows the
supply of water for generation to be matched with the demand for electricity over the
year. In addition to compensating for extreme annual and seasonal variations in water
supply and power needs, storage can also provide a reliable source of water during
periods of drought and flood relief during periods of high inflow.
Water levels in annual storage reservoirs fluctuate with the yearly cycle of water supply
and electricity demand. Levels are generally lowest in early spring, prior to the snowmelt.
Subsequently, they rise through the spring to a maximum, fall off to a low during the
summer, and then recover to a smaller peak in the fall before declining over the winter.
In other cases, water levels continuously rise from a pre-runoff low to a peak in early fall.
Multi-annual reservoirs are filled or emptied over several years, with an average annual
drawdown that is usually much less than the maximum for the period.
The degree and rate at which reservoir levels change depend on the type of dam/reservoir
(e.g., forebay, and headpond), climate, topography, and other factors. Reservoirs with
limited storage capacity are less subject to annual or seasonal water level changes,
operating instead through daily and weekly fluctuations in water level. Conversely,
run-of-river facilities try to maintain the reservoir at a constant level (i.e., no water level
fluctuations), by matching the discharge to the inflow. Water levels are generally kept
close to the full supply level to maximise head.
Regulating gates and/or generating units control the amount of water flowing out of the
reservoir. Reservoir water levels vary within a range defined by a minimum (low supply)
and maximum capacity (full supply) elevation, with a normal operating level. The process
of lowering the reservoir level is called drawdown, while the process of raising it is called
ponding (filling). Facilities are often bound by legal, regulatory, or other requirements that
specify maximum and minimum elevations and, in some instances, drawdown and
ponding rates and the timing of water level variations.
Fish and Fish Habitat Effects
Reservoirs can be created from rivers or lakes. When created from riverine habitat, we
can see a shift in fish species (from river to lake species). However, many reservoirs in
Canada were created from existing lakes and the fish composition after filling remained
much the same. For example, monitoring the reservoirs of La Grande Complex in
Quebec revealed that, in most of these reservoirs, fish composition did not change
significantly after filling. Some species do well in a reservoir environment, including kokanee,
lake whitefish, walleye, pike and smallmouth bass. However, several of these species spawn
along shores and in shallow streams that are especially vulnerable to drawdowns.
Another aspect of reservoir creation is the nutrient input associated with organic
matter decomposition after initial filling. For a period of several years, this nutrient
input translates into increased primary production, zooplankton production and fish
biomass. After this period, which lasts a few years, fish biomass generally returns to
pre-impoundment levels.
Page 24
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Reservoir operations, however, can have negative effects on fish and fish habitat.
The extent of these effects is a function of reservoir hydrological characteristics and
hydroelectric function, as well as physical features, such as shoreline slope, mean
and maximum depth, flushing time, and discharge and drawdown elevation.
Typically, both the spring freshet and fall rains contribute to ponding. In either case,
where reservoir shoreline spawning occurs, the precise timing of reservoir filling may be
critical. If filling occurs too late, shoreline and shoal spawners may not have access to
spawning habitat in littoral zones (the productive shallow areas of the reservoir) or
tributary streams. If the reservoir is filled too early, there may be no storage available for
the late spring flood. Ponding can eliminate the beneficial effects of the freshet on gravel
cleaning and recruitment and riparian habitat maintenance downstream of the reservoir.
Changes in water level can alter riparian and littoral zones, depending on bottom slope,
water quality, and substrate. High water levels might reduce littoral productivity by
restricting light penetration to the reservoir bottom in cases of steep bottom slopes or high
turbidity and can flood tributaries, eliminating or reducing fast water habitat. Low water
levels could limit littoral productivity and access to spawning tributaries, or may elevate
littoral production if the corresponding bottom slopes in the littoral zone are gentle and
the substrate is favourable. Rapid water level fluctuation is more limiting to littoral
production if organisms do not have time to adjust. In some cases, higher reservoir levels
can benefit fish populations by providing overwintering habitat. The large winter
drawdowns that characterize most Canadian storage reservoirs can result in dry littoral
zones and the freezing or desiccation of eggs laid in the fall. These drawdowns may also
improve some spawning substrates by exposing them in the subsequent spring and
summer to the cleaning action of air, rain, and waves.
In some reservoirs, rapid fluctuations in water levels during flooding or major drawdowns
can displace or strand fish. In contrast, floodplain wetlands rely heavily on seasonal water
level changes, and summer levels that are too constant can turn productive wetland into
terrestrial habitat.
The extent of these effects is largely a function of the physical attributes of the reservoir.
For example, reservoirs with steep banks generally have limited littoral zones, so that they
are affected differently by water level changes than reservoirs with flatter shores. Deeper,
stratified reservoirs can have a greater impact on fish through their effects on water quality
and temperature. These reservoirs can become thermally stratified in the summer, with
zones of warmer and cooler water, which may become anoxic (oxygen deprived) in their
lower levels at certain times of the year. Occasionally this can prevent fish from using the
affected strata and cause dissolved oxygen problems downstream, which may cause stress,
reduced productivity and, in the extreme, fish mortality. The degree of impact depends on
the elevation of the outlet structures and their seasonal utilization to release water. In
contrast, shallow reservoirs and run of river facilities cause little or no change in water
temperature and usually have a stable elevation in order to optimize head.
A potential persistent effect from reservoir creation may be the creation of methyl mercury
as a result of the initial flooding. This form of mercury bio-accumulates and can result in
elevated mercury levels in both reservoir and downstream fish for many years. However,
following a return to background levels, most established reservoirs have no significant
mercury issues. In recognition of the potential issue, various utilities have participated in
cooperative studies with the federal government (See Appendix C: Selected Readings for
examples of this work).
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 25
Other Considerations
Reservoirs are a key component of river flood management strategies. These strategies
require maintaining the reservoir at a low level as late as possible into the spring for flood
control purposes, which can reduce littoral zones and block tributaries for spawning.
Riparian erosion and shoreline vegetation are also issues to be considered in
hydroelectric operations. Erosion can result in soil movement and potential dust storms
in the extreme case.
Recreational activities, including swimming, boating, and fishing, are other important
considerations for reservoir operations. Reservoirs may be managed to forego drawdowns
during the summer that can interfere with these activities. Maintaining reservoir levels for
summer recreation is complementary with fish and habitat requirements.
For some hydroelectric facilities, an important water management objective is the control
of water elevations for shipping and navigation. Reservoir levels can be managed to
prevent grounding and damage to boats, locks, and other structures. Reservoir
management can also affect the timing of ice formation, as well as the stability and
smoothness of ice cover.
Reservoir operations can affect private property and infrastructure by altering shoreline
processes and causing sedimentation
and erosion. A buffer of land
surrounding the reservoir is generally
Sample Practices
reserved to accommodate the
• A recent BC Hydro Water Use Plan identified
fluctuating water levels required for
productive littoral zone as a key objective, and
generation, flooding, and geotechnical
the resulting operating plan increased littoral
stability. However, in some floods, the
productive potential from 30 to 860 hectares.
buffer level may be exceeded,
• Reservoir drawdown is restricted for a 30-day
impacting property and infrastructure,
period after the spring peak at Saskatchewan’s
such as docks, boat ramps, and water
E.B. Campbell Hydroelectric Station to protect
pike spawning habitat in Tobin Lake.
intake structures.
Large reservoir drawdowns can result in
dust storms, bank slumpage, and loss
of riparian vegetation. The drawdown
cycle is normally long enough to
preclude the establishment of natural
vegetation that is either aquatic or
terrestrial in nature.
In recent years, endangered species
or species at risk have been given
increased profile. Habitats containing
plants or wildlife at risk will need to
be given additional consideration in
the future.
Page 26
• Manitoba Hydro funds and conducts
monitoring of both methyl mercury and
greenhouse gas levels in its reservoirs.
• Ontario Power Generation controls winter
drawdowns for incubating lake trout eggs and
fry in a number of lakes.
• Great Lakes Power Ltd. has adjusted the
drawdown limits and timing for some of its
upper storage lakes, contributing to an
improvement in resident walleye fisheries.
• Nova Scotia Power limits drawdowns in
several reservoirs of the Black/Gaspereau River
system during late May to late June to support
small mouth bass spawning.
• New Brunswick Power has agreements in
place to limit drawdown levels in some
reservoirs for the protection of lake trout
spawning areas.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Examples of Practices
Operations:
Operating protocols incorporate regulatory, environmental, and other requirements for
reservoir management. Protocols can range from informal regional agreements with
ratepayers or resource users to major formal agreements involving reviews and
modifications of water licences. Rule curves are typically used to define operating ranges
(water levels and timing) for the reservoir to meet power generation, flood control, ice
management, fish and fish habitat, recreation, heritage, and other water use requirements,
as appropriate, throughout the year. The more complex the system, the more detailed the
rule curve. An example of a rule curve is provided in Figure 3.1.
FIGURE 3.1
25% exceedence
75% exceedence
Operating constraints for fish and fish habitat considerations can take several forms,
as follows:
Target reservoir levels may be set to maintain adequate water levels for spawning,
egg incubation, and other fish requirements. These targets must be managed
together with target levels and requirements for generation as well as other water
uses, such as recreation, heritage needs, and navigation.
Drawdown restrictions on the extent, rate, and timing of reservoir drawdowns are
often used to prevent the stranding of fish and damage to spawning habitat. For
example, to protect fall spawning species, winter drawdowns may be limited
relative to the spawning and incubation elevation; alternatively, drawdowns below
the spawning/incubation level may be restricted to the spring. Again, such
restrictions must be balanced against the requirements for power generation and
other water uses, especially flood control.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 27
Early spring filling of reservoirs can help ensure fish access to spawning tributaries
or floodplain wetlands. However, there may be a conflict with flood management,
since late filling may reduce the risk of a spring flood. In some cases, there is no
opportunity to influence storage timing, as it is driven by climatic conditions.
In cascading systems, flows from the upstream generating station may be
occasionally optimised in the tailwater to facilitate critical life history activities,
such as spawning for fish species in the downstream reservoir.
Other Measures to Minimise Effects:
Research and monitoring can identify measures to help mitigate the fish and habitat
impacts of reservoir operations. Research is being carried out in areas such as reservoir
productivity, wind and wave erosion, fertilisation studies, the value of riparian vegetation
planting, and modelling of mercury levels in fish. For example, studies have been
initiated to attempt to establish vegetation in some reservoirs that can accommodate
extended periods of inundation or desiccation. Other research topics include developing
fish population response models to reservoir management practices, and the use of marsh
areas and floating islands to retain habitat during drawdowns.
Shoreline stabilisation (e.g., installation of riprap, riparian revegetation) can control the
effects of erosion and sedimentation on reservoir shorelines and ecosystems.
Various measures can be undertaken to compensate for reservoir impacts that have
already occurred. Reservoirs can be fertilised in some instances (i.e., deep reservoirs with
poorly developed littoral zones and limiting nutrient levels) to ensure the continued ability
of the ecosystem to support populations of fish and other aquatic species. In cases where
dissolved oxygen levels are found to be unsatisfactory, bubblers or other means of
aeration may be employed to increase oxygen in the water column. For areas impacted
by erosion, annual seeding by grasses has been carried out to improve air quality,
aesthetics, and habitat for fish and wildlife.
Habitat development can replace spawning grounds affected by reservoir level changes.
For example, to assist reservoir-spawning species, spawning shoals can be created below
the reservoir low water level to draw spawners below the zone of risk from water level
fluctuations. For stream-spawning species, suitable substrates can be placed in tributaries
upstream of backwater effects from the reservoir. Downstream of the reservoir, gravel can
be added to the river to offset loss in gravel recruitment from upstream sources. As an
alternative, artificial side channel rearing or spawning channels may be created. These
strategies are often referred to as "compensation", for example, in the Federal Policy for
the Management of Fish Habitat. They can also, however, be used to create habitat where
there has been no habitat loss, or to create habitat for species that may be considered by
some stakeholders as "more valuable".
If habitat restoration or development is not feasible, fish can be raised in hatcheries and
then stocked in reservoirs, to replenish populations and provide recreational fishery
opportunities as a side-benefit. For most stakeholders, including both utilities and
Fisheries and Oceans Canada, this is considered this to be an option of "last resort".
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.2
FLOW MANAGEMENT
A power system is operated to consistently generate the electricity required to meet
customer demands at all times, regardless of weather and other conditions. Electricity
generation comprises two basic components, base load and peaking. The base load
component is the backbone of the system – the regular, constant generation required to
satisfy the minimum electricity demand over time. Block loading is a sub-component of
base load operation designed to respond to fluctuating seasonal demand. The peaking
component of generation augments the base load by providing the power needed to meet
hour-to-hour and other short-term variations in demand. Hydroelectric generation is an
important contributor to the power system, and is used for all three kinds of operations,
each utilising different flow regimes.
The operation of a hydroelectric system necessitates some control of naturally flowing
waters. Control is achieved through the construction of dams and the formation of
reservoirs and headponds. Dams may be used to capture water for subsequent release, or
to divert water along another route or to another watershed. Retaining or impounding
water initially affects flow in two zones: (1) the original riverine habitat that is transformed
to lacustrine habitat with the formation of a reservoir; and (2) the riverine habitat
downstream of a dam through which flow is altered in timing and magnitude and possibly
temperature. Protection of fish and fish habitat in downstream areas is one of the many
considerations of flow management.
The ability to manipulate stored water is attained through the use of water control
structures, such as spillways, gates, canals, and the hydroelectric generating facility itself.
Creating an artificial water control system in the natural environment further impacts both
fish and aquatic habitat by forming obstructions and restrictions to flow, by temporally
redistributing flow (hourly, daily, weekly, monthly, annually), and by impacting the
physical and chemical qualities of the water. These impacts can conflict with the life
history activities of various fish species that evolved under natural flow conditions. The
fact that many dams were built in impassable natural barriers, such as waterfalls, must
be considered when assessing the net impact of hydroelectric facilities.
Flow management is the process used to reconcile the demands of the various
hydroelectric operations with the resultant downstream flows and their effects.
Hydroelectric generating facilities that contribute to the base and block loading
requirements of the system (and that also have significant storage capacity) affect
long-term water flows, while hydroelectric peaking operations affect short-term flows.
When the finite amount of storage capacity is exceeded, the resulting spill conditions
will increase downstream flow. For reasons of public safety, spilling or sluicing is further
used to increase reservoir storage capacities prior to high precipitation events, which
otherwise might compromise dam safety regulations. Synchronous condensing
operations that are used for voltage regulation in the transmission system may potentially
impact water quality downstream of hydroelectric generating facilities. The following
sections will discuss in detail the different aspects of flow management as they pertain
to hydroelectric operations.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 29
3.2.1 Long-term Flow Management
Description
Long-term flow management involves the reshaping of natural flow regimes to meet
seasonal, annual, and multi-annual electricity system demands, while also providing for
downstream fish, fish habitat, and other requirements. This flow management is an
essential practice considering the conflicting nature of electricity demand and water
availability. In general, demand tends to be higher in the winter and lower in the summer.
Conversely, in an unregulated river system, water inflows are typically low during the
winter, increase significantly in the spring, and then decline again in the summer. (See
Figure 3.2) Inflows may then increase again in the fall during heavy precipitation events.
Seasonal water flow is managed to generate electricity, maximise the capture of water, and
balance environmental considerations with the needs of other resource users.
FIGURE 3.2
Abitibi River - Otter Rapids HGS
Mean Monthly Discharge (CMS)
1000
ESTIMATED NATURAL
500
EXISTING REGULATION
0
J
F
M
A
M
J
J
A
S
O
N
D
Both the timing and magnitude of releases from hydroelectric facilities can be
substantially different from those of natural hydrological cycles. This variation can lead to
the development and implementation of prescribed flow regimes, including flushing flows
to preserve river morphology and minimum flow releases, or instream flows, established
to protect aquatic resources downstream of the facility. Instream flows may also be
established for areas downstream of diversion or storage dams that are not directly
affected by generating operations, but are impacted by the long-term redirection of flow.
Many hydroelectric stations do not have specific instream flow requirements. For
example, they may discharge into a tidal area, or may not have sensitive fish or navigation
requirements downstream of their dams. Alternatively, there may be other factors (e.g.
existing approvals, past agreements, management plans, historical provisions, physical
limitations) that negate the need for specific flow regimes. In the case of run-of-river
stations, discharge regimes tend to be similar to the unregulated river. Regardless of the
application, instream flows can be an important factor in long-term flow management.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Long-term flow management is the process by which environmental requirements,
including fish and fish habitat, are balanced against electricity generation requirements.
Where applied, prescribed flow regimes are a tool to ensure the protection of aquatic
resources while maintaining the economic viability of the hydroelectric facility.
Fish and Fish Habitat Effects
Long-term flow management has predominantly positive effects on fish and aquatic
habitat by redistributing water flows throughout the year. Many natural systems typically
have very low flows during the summer and winter, limiting the productive capacity of
the stream and, in some cases, reducing water quality. Storing water from the spring flood
or fall rains and releasing it in the late summer and winter compensates for this natural
phenomenon, and can maintain higher volumes of habitat and higher fish populations, as
well as improving water quality. The primary benefit of keeping a base flow in the river is
the continued viability of fisheries that would otherwise be severely impacted through a
lack of habitat, increased water temperatures, and easier predation.
The smoothing of water flows also optimises available habitat for benthos, an important
food source for fish, as well as critical spawning habitat. In some cases, however,
smoothed hydraulic regimes can degrade habitat through changes in the annual cycle of
sediment movement and deposition, which can lead to bank erosion and reduced
morphological complexity. Alluvial channels rely on annual high- and low-flow periods
to wash away finer substrates, recruit new, loose substrate, and redistribute it along the
channel. Without this natural process, substrates can become more homogeneous and
spawning success may be reduced in some instances. In addition, changes in flows can
modify erosion and deposition patterns, leading to deposition of silt at the mouths of
tributaries, resulting in the loss of access to habitat. The provision for annual flushing
flows, often in conjunction with spilling practices, can mitigate such impacts.
The extent of the positive benefits, however, may be dependent on the site, the fish
species involved, and other project specific considerations. Specifically, the potential
effects of a facility that is located far upstream of the river’s estuary will be different in
both nature and scope than for a facility that is just above the head of tide.
Other Considerations
Facility constraints, in particular the relationship between installed generating capacity,
water supply, and storage capacity, will have a large influence on the ability to address
downstream minimum flow requirements. For example, a small storage reservoir may not
be able to store enough runoff in the spring to provide water for both electricity purposes
in the summer and instream flows for fish in the fall. Likewise, plant capacity may
constrain the amount of water that can be passed in any particular season.
Long-term weather patterns are a key consideration for water supply. If precipitation is
less than anticipated, it may not be possible to meet minimum flow requirements. Given
factors such as climate change, weather patterns may not be similar to the historical
hydrograph.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 31
Other factors that must be examined in long-term flow management include dam and
public safety, power requirements during emergencies, and the effects of fluctuating water
levels and shoreline processes on property and infrastructure. Further considerations
include water allocations for stakeholders, comprising industry, commercial fisheries, and
the numerous types of recreation activities that utilise water resources.
Examples of Practices
The determination of the optimised use of water, and therefore the appropriate
maintenance flow, requires a careful consideration of many factors. This determination is
normally part of system operations (see Section 2.2), which evaluates how a particular
plant will contribute to the annual system power requirement. If instream flows are
deemed to be desirable for a facility, then the process for determining and altering longterm flows consists of the following basic steps:
1. Clearly describe the system, including its opportunities and limitations related to flow.
This may involve the collection of information on physical conditions, hydrology, past
practices, facility constraints, and the impacts of instream flow requirements on other
water management objectives.
2. Identify fish and other aquatic
species and evaluate the
sensitivities regarding related
habitat.
3. Examine key factors, including data
availability, regulatory
requirements, other water uses, the
cost of providing instream flow, and
resource priorities.
4. Choose the suitable instream flow
methodology (see Appendix D) and
use it to identify a flow schedule,
adjusting to allow for optimisation
with other water uses.
5. Evaluate the flow schedule to
determine the impacts on
generation and power costs, and
make flow alterations where
appropriate. In most cases, the
final flow schedule will be based
on a combination of science and
negotiation to address other water
uses in the area. If the power costs
are prohibitive, then the facility’s
operating regime will be not be
altered.
Page 32
Sample Practices
• New Brunswick Power has agreements in
place to provide predetermined flows
downstream of some reservoirs, ensuring
adequate water for migration and spawning of
Atlantic salmon.
• Nova Scotia Power has developed a specific
flow plan for the Gaspereau River system to
facilitate upstream migration of smelt,
alewives and Atlantic salmon.
• Great Lakes Power Ltd. releases 17 cms yearround from its Scott Generating Station to
assist rainbow trout, walleye, salmon, carp,
and sturgeon fisheries.
• A weir built by Manitoba Hydro at Cross Lake
is helping the recovery of whitefish
populations by increasing minimum water
levels and moderating seasonal fluctuations.
• SaskPower is monitoring dissolved oxygen
levels at the Nipawin Generating Station to
determine whether action is needed to protect
an important downstream walleye fishery.
• BC Hydro has implemented a flow agreement
on the Alouette River that balances a yearround minimum flow release for fish habitat
and target reservoir elevations for summer
recreation and flood control needs.
• At various dams, Ontario Power Generation
has enhanced leakage with shims, to provide
a minimum flow to maintain aesthetics, water
quality, and fish habitat.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Operations:
Where operational changes are feasible, these can be achieved in several different ways.
In the case of important fisheries and other targeted species, minimum or seasonal
instream flows may be incorporated into rule curves and operating protocols. Typically,
minimum flows are set for a period of one to several months related to spawning activity –
i.e., minimum spring or winter flows. Minimum flows provided downstream of diversion
or storage dams may be set for the full year, as the downstream habitat in these areas may
not benefit from generating operations.
For fisheries or sensitive stocks which may be identified as important by regulators,
operators or others, generating stations may be block or base loaded for a period of time
to provide minimum flows during spawning and egg incubation. The facility may be
operated to lead fish to spawn at low elevations in the channel where eggs will not be
exposed during future operations.
Even if water levels are adequate, spawning and other activity may be inhibited by factors
such as sedimentation. Flushing flows, or short pulses of high water flows, can be used
periodically to clear silt, condition spawning substrates, and in some cases encourage fish
migration. Minimum spring releases can also reduce sedimentation.
Water releases to simulate the natural hydrograph have also been utilised to provide
appropriate triggers for seasonal migration or spawning.
During periods of unusually low water flows, utilities may undertake consultation to
advise and confer with regulatory agencies and other key stakeholders concerning special
instream requirements and constraints.
A variety of methods have been used for instream flow assessment. The choice of
methodology will depend on various factors, including the availability of biological data,
potential effects of operations on fish and fish habitat, potential effects on other water
uses, and the cost of providing instream flow (financial viability of the producer). The
following list provides some examples and brief descriptions of instream methodologies:
• Professional judgement – setting instream flow based on the experience of
biologists or other multidisciplinary professionals
• Aquatic Base Flow – a hydrological method that uses historical flow data to
determine the median flow for the lowest flow month
• Tennant Method – a hydrological method that prescribes eight categories of
stream flow as fixed percentages of the mean annual flow
• Wetted Perimeter Method – a hydraulic method that assumes a relationship
between the wetted perimeter (narrowest wetted bottom of a stream crosssection) and available fish habitat
• Habitat Quality Index – uses statistical analysis to correlate environmental
features of a stream with fish population size
• Instream Flow Incremental Methodology (IFIM) – a combination of integrated
planning concepts for water supply, analytical models of chemical and
physical parameters, alternatives analysis, and negotiations, with criteria based
on the Physical Habitat Simulation program (PHABSIM)
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 33
• Adaptive Management – an interactive process that tests the implications of
alternative management options, most often used in high resource value
situations, to test the implications for fish and fish habitat
• Regionally adapted methods – setting instream flow based on local data and
criteria, often customising other methods.
A description of each of these techniques is provided in Appendix D.
Other Measures to Minimise Effects:
When adequate instream flows and operating changes are not feasible or desirable,
compensation measures may be used to address negative impacts on fish and fish habitat.
Habitat enhancement may be undertaken to increase habitat area and/or quality in order
to maintain productive capacity of the watershed. Some situations may warrant a
combination of instream flow and habitat enhancement techniques.
In cases where fish stocks would benefit from improved habitat, side or mainstem channel
habitat improvements may be carried out as an alternative to instream flow releases.
Where spawning shoals or other concise habitats are shallow and threatened with
exposure during hydroelectric operations, the shoals may be lowered to an elevation
below that provided by the instream flow. Alternatively, new artificial shoals may be
constructed deeper in the channel.
Weirs may be constructed downstream of a dam to create a backwater effect and
maintain water level elevations above those offered by instream flow.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.2.2 Short-term Flow Management
Description
The demand for electricity varies throughout the day and week, in rhythm with people’s
lives. Demand is normally lowest in the early morning and late evening and on
weekends, and highest on weekdays from breakfast through dinnertime. Hydroelectric
facilities are particularly well suited to meet rapidly fluctuating demand, due to their
almost instantaneous response times.
The process for making short-term changes in generation in response to demand is known
as peaking. This is accomplished by increasing or decreasing water flow to achieve the
desired generation sometimes within a matter of minutes. Operations may be scheduled to
peak one or more times a day and may vary in duration, depending on the short-term
demand for electricity. Certain hydroelectric units are configured to operate for only a
few hours per day at the time of maximum demand. Since each unit is unique in its
generating capability and flexibility, the key operating decision lies in planning when and
where to change facility production to meet system-wide demand.
Some hydroelectric stations may be dedicated to peaking operations. For such facilities,
the turbine capacity will be much greater than the normal flow of the river. During lowflow seasons, there must be upstream storage to accumulate flows over a few hours until
sufficient volume exists to run the station. Downstream flows tend to change in increments
commensurate with the size of the turbine units. Peaking effects on downstream flow tend
to be most extreme when river flows allow all the units to be run for about 12 hours per
day. These effects on flow attenuate as the distance downstream from the station increases.
Electricity producers must be able to provide peak power for reliability and safety of the
power system. Peaking is essential to ensure system stability and maintenance, and to
meet society’s growing power requirements.
Short-term flow fluctuations may also arise from the operation of non-power discharge
facilities, including spillways, sediment sluicing gates, and low-level outlets. Operation of
these facilities is generally determined by decisions regarding flood control or other
considerations, independent of energy demand and plan reliability. Although this section
focuses on short-term flow fluctuations arising from powerhouse operations, some of the
effects and practices outlined here may also apply to non-power discharge facilities.
Fish and Fish Habitat Effects
Although fluctuations in water flow happen naturally in an unregulated river system, those
occurring in a regulated system may be more abrupt or may take place at different times.
Such differences can result in rapid and extensive fluctuations in microhabitat conditions
and downstream fish displacement.
An extreme decrease in flow may dewater existing habitat and create unconnected pools of
water. Fish can become stranded, either on mainstem gravel bars or in side channels and
isolated depressions in the streambed, often resulting in increased predation and death.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 35
Some species, such as walleye and pike, may be more vulnerable because they spawn
along shores and in shallow waters. Dewatering may also expose incubating eggs to
freezing and desiccation.
An extreme increase in flow may displace fish (especially eggs and juveniles) and the
aquatic invertebrates on which they feed. The mobilisation of gravel and bank erosion
may cause physiological stress and the introduction of fine sediments that can suffocate
incubating eggs. High flows may also flood riparian areas, reducing shoreline vegetation,
bank stability, and the availability of organic debris.
Other effects of rapid flow fluctuations include disruptions to spawning, migration, and
other behaviour resulting from changes in water velocity, depth, and temperature.
Other Considerations
The facility configuration and design are important factors in determining options for the
rate and magnitude of flow changes. Most turbines are not equipped to provide gradual
flow changes (depending on their type, size, and number of units), which limits the
operator’s ability to smooth flow transitions. A number of other factors may affect the
provision of gradual flow changes, including: changing the number of turbines in
operation at a multi-unit facility; rapid shutdowns due to mechanical and electricity
problems; and low-flow start-up and unit cycling.
The peak flows and relative size and design of the impoundment and other structures may
also limit the ability to moderate the rates and magnitude of flow changes. In some cases,
an upstream generation station may peak and, because of headpond storage limitations,
the downstream utility will be forced to follow the same operational pattern. On the other
hand, cascading systems also serve to mitigate some of the elevation effects of peaking.
There is a need for basin-wide water management plans to facilitate operations while
addressing environmental and social concerns.
Peaking constraints on individual facilities also depend on what alternatives exist to
produce the required electricity elsewhere in the grid.
Rapid changes in the water regime can also impact other downstream users of the
watershed. Dramatic flow changes and the associated erosion and other alternations to
shorelines may affect recreational activities and private property and infrastructure, and
may create public safety concerns. Peaking operations can also pose a threat to nesting
waterfowl and other wildlife with habitat in and around rivers and streams.
Examples of Practices
Impact assessment is the first step in deciding whether operational and other actions are
needed to address the effects of peaking generation. An overview assessment uses
available data to provide order-of-magnitude estimates of fish and habitat effects, as well
as rough estimates of the costs of operational changes. If required, more detailed flow
peaking studies can be completed that collect site-specific data and describe and assess
the fish-related effects. The data from both processes is then used to decide whether
actions are recommended, based on biological impact, local and system electricity
demand, legislative requirements, facility constraints, and expected costs and benefits.
Page 36
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Operations:
If operational change is selected as a
reasonable option, then flow guidelines,
protocols, or schedules can be
developed to minimise the effects on
the aquatic environment, while still
meeting peak power and other
requirements. These guidelines can be
prepared using some combination of
professional judgement, standardised
or site-specific fish protection criteria,
and follow-up evaluation and refinement
work. They provide operating
instructions on the allowable timing
and magnitude of flow changes to
accommodate fish and habitat needs.
The schedules must take account of the
hydraulic response of the river to
upstream changes and constraints on
facility units and structures for making
gradual flow changes.
Flow schedules can include provisions
for base flows, alterations to the rate of
change in flow (ramping), and changes
to the timing of peaking operations:
Minimum instream flows can be
specified during critical times,
such as spawning periods (see
Section 3.2.1 on Long-term Flow
Management practices).
Sample Practices
• Manitoba Hydro has modelled and
monitored diurnal flow fluctuations
downstream of the Limestone Generating
Station with respect to fish movements into
tributary streams and effects on the Nelson
River estuary.
• Ontario Power Generation implements
winter peaking constraints on the Nipigon
River to protect brook trout eggs during
incubation.
• Great Lakes Power Ltd. has a year-round base
flow of 7.5 cms and seasonally varying
ramping rates that have maintained a highquality brook trout fishery.
• During rare drought conditions on the
Missisagi River, Ontario Power Generation
has operated during three separated periods
in the day to provide a 35 cms daily flow to
protect salmon spawning and egg incubation.
• Nova Scotia Power times and closely
controls flow changes from Carleton
Reservoir in the Tusket system in late
June/early July, a critical stage of alewife
upstream migration, to prevent stranding.
• Newfoundland and Labrador Hydro provides
summer and winter releases of 2.6 cms and
1.3 cms, respectively, from the Upper
Salmon River facility to protect critical
spawning habitat in the West Salmon River.
Ramping refers to the operational process of increasing generation and flow
discharges (upramping) or decreasing generation and flow discharges (downramping)
to achieve less dramatic variation in water flows. The rate at which ramping is
achieved is important. Generally, slower rates of change producer fewer effects.
Changes to the peaking time of day of day or frequency can be made to
smooth out flow and elevation fluctuations downstream of the facility. Since
peaking effects on flows and water elevations attenuate with increasing
distance downstream, multiple peaks distributed throughout the day will have
a moderating influence.
Continuous base flow releases may also serve to offset the impacts of peaking
requirements. In these situations, a base flow is passed downstream of the
generating station in accordance with approvals given by the regulator. The base
flow is equivalent to the minimum flow that can be safely passed through one of
the generating units sufficient to cover facility operating costs plus a minimum rate
of return. Often, this minimum flow is greater than that which would occur during
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 37
the driest period of the year, so that it provides a greater level of productivity in the
stream or river throughout the year.
Other Measures to Minimise Effects:
Adjustments to peaking operations may not be enough to address fish stranding in every
case. Channel modification – for example, reshaping river bars and blocking access to
side channels – has been used in conjunction with peaking schedules. A notch can be
built in the channel to provide refuge for fish during severe decreases in flow.
Fish salvage is another supplementary option for dealing with stranding. However, to date
facility ramping and salvage operations have not been used together extensively. Salvage
operations are not practical on a daily basis.
Enhancement measures, such as habitat improvement and fish stocking from hatcheries,
can also support peaking changes. Weirs may be used to re-regulate the flow and
current.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.2.3 Spillway Operations
Description
Spilling is a normal and required operation for hydroelectric generating facilities, and all
facilities are provided with a means of spilling surplus water from the reservoir (e.g., a
spillway) as one way to protect the generating station from flooding. The amount and
frequency of spill depends on the station capacity and the flow of the river. At small
stations, where the flow of the river normally exceeds turbine capacity, there may be an
almost constant spill. At large stations, especially dedicated peaking stations, where the
turbine capacity far exceeds the mean flow of the river, spilling may be a very rare event.
Hydroelectric systems are generally operated to avoid spilling because it represents a loss
of potential generation and revenue. However, spilling will be required when flows
exceed the capacity of the station and there is no available upstream storage capacity,
when load rejection occurs (unplanned instantaneous shutdown of a unit), or when the
station turbines are taken out of service for maintenance. If there is no available storage
and the station is required to spill, the operators will have little control of the onset,
magnitude, or duration of the spill. However, they may be able to control the cessation
(or downramping) of the spill.
Pre-spill planning may increase the amount of control that a producer has on the extent
and timing of spills. If storage is available and high-flow events such as the spring freshet
can be predicted, the operator can delay the onset of the spill and reduce its magnitude
by creating storage capacity in upstream reservoirs prior to the event (see Section 3.1 on
Reservoir Management). When spills are planned for maintenance purposes, the operator
can control the onset, magnitude, duration, and cessation of the spill.
When river flows decline to less than the safe operating limit of the turbine, there will be
no flow in the spillway, unless a minimum flow is specified to protect fish and fish habitat
or to meet other water use objectives. The channel downstream of the spillway may
dewater if there is no backwater effect from the station tailwater or a downstream dam, as
in a cascading system.
Spillway channel design varies substantially from site to site. The spillway may be
adjacent to or remote from the station. If the station and the spillway are constructed
together within the original bed of the river and the spillway channel is contiguous with
the tailwater of the station, spill effects on fish habitat may be restricted to a very small
area immediately downstream of the spillway. If the spillway is remote from the station,
the spillway channel may be stagnant or even dry when river flows are less than the
capacity of the station until the spillway channel merges with the station tailwater.
Most facilities have only one spillway, but some may have two or more, especially where
diversions have occurred. In this case, the operator may be able to divide the spill
between the two spillways, providing more control over downstream impacts. Often there
is a spillway around the station that is used for fine control and a larger spillway that is
used only for high (flood) flows.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 39
Most spillways are surface spillways, but spillways for large reservoirs may draw water
from a considerable depth, with implications for downstream water quality.
Many spillways cannot be automatically or remotely controlled and require a crew to
make manual adjustments. This greatly reduces the flexibility of control by the
hydroelectric producer.
Fish and Fish Habitat Effects
The fish-related effects of spillway operations may vary dramatically with the spillway
configuration and the nature of fish and fish habitat. The spillway channel may or may
not contain significant habitat, depending on the area, gradient, frequency of spill,
leakage, and backwater effects. High gradient spillways with infrequent spills may be
dewatered most of the time, making them unsuitable habitat. Fish may only occur in
these spillways during infrequent spills, when they are attracted by the high flows, or as a
result of entrainment through the spillway from the reservoir or headpond. If the spillway
contains large pools, fish may persist in it for long periods after the spill stops, although
spawning may not occur.
If gradients in the spillway are low and there are frequent spills or a backwater effect, the
spillway may constitute fish habitat. Such habitat is characterised by large fluctuations in
flow and water levels that can impair the productivity of resident fish. When flows are
low, fish become concentrated in pools where predation can be high and water quality
may become a problem. When flows and current velocities are high, smaller, weaker fish
will tend to be displaced downstream. There may be spawning in the spillway and
dessication may occur if flow is terminated.
Stranding is a special problem for upstream migrating fish since spills often occur in the
spring and fall, the two seasons when many Canadian fish species undertake upstream
spawning migrations. If the fish spawn in the spillway channel, eggs may be exposed
when the spill is ended. These impacts may not be significant in many cases as fish have
had to adapt to natural variations in flow regime, and spills are usually of short duration.
Similarly, conditions in the river during a spill may not be substantially different from
those in the river during a freshet prior to the dam’s construction.
Although entrainment of resident stocks through the spillway does occur, it is not
considered to be a critical factor influencing the biological integrity of fish populations.
Downstream migrating juvenile salmonids bypass dams more successfully using spillways
than passing through turbines, and the manipulation of spillway flows to attract and pass
fish is routinely done on both the east and west coasts. Spillways are not considered to be
a serious cause of fish mortality.
Depending on the geomorphology of the spillway channel and the design of the
spillway structure, the spill may lead to the mobilisation of debris, vegetation, and
sediment that may be transported downstream. The movement of gravel may benefit
spawning substrates, but may also erode the spillway channel, reducing or degrading
downstream habitat.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
For dams with deep plunge pools, spill discharges can alter water quality through
increased concentrations of dissolved gas. Dissolved gas supersaturation (DGS) occurs
when air is entrained in water while it is passing through a spillway and is subsequently
plunged into a deep pool at the spillway’s base. During this process, the air is
pressurised; forcing nitrogen and other gases to dissolve in the water at supersaturated
levels. In order for total gas pressure to increase, it is necessary that there be entrained
air, as well as a deep pool below the spillway. The pressure exerted on the gas bubbles
entrained in the water is directly related to the depth at which the air bubbles are forced.
In British Columbia, for example, water quality guidelines have been developed with the
objective of limiting total gas pressure to less than 110% in deep water and 103% in water
of a depth of less than one metre.
Gas supersaturation can lead to gas bubble trauma, physical impairment, disease, and
mortality in fish, with impacts varying by species and age class. The presence and
severity of DGS depends largely on dam design and operation.
Depending on where water is drawn from the reservoir, spilling can also create
fluctuations in downstream water temperature to which fish are sensitive. The
temperature of water releases can differ considerably from downstream river temperatures.
Temperature fluctuations tend to be greater in the case of large stratified reservoirs or
forebays that discharge (cooler) water from closer to the bottom.
Other Considerations
The design of the spillway discharge is instrumental in determining the control that the
producer has over the spill. Gates may be manually or automatically controlled, or
controlled from onsite or from a remote location. There may be several smaller gates that
allow an incremental increase in spill or only a few large gates. It may be possible to
progressively open a gate, or the gate may operate either closed or fully open.
“Free crest” spillways are designed to automatically spill water for flood control without
human intervention. In certain extreme flood situations, there may be a “fuse plug” on
the reservoir that releases the excess flows to preserve the integrity of the main dams.
These types of spillways do not allow control of the spill to benefit fish habitat.
The relative size and storage capacity of the impoundment and other structures are key
factors in spill management. The siting and design of the spillway channel have a large
bearing on fish habitat and subsequent effects on fish. Spillway channels remote from the
original channel may be subject to significant erosion. Spillway discharges may be
designed to reduce the energy of the spill and subsequent erosion (e.g., spillway deflectors
or flip bucket spillways).
Initiation of a spill may have public safety implications that require some system of
communication with other downstream users. Rapid fluctuations in flows can be a
problem for boaters, canoeists, and kayakers. In addition, public safety may be affected
by winter spill releases that impact the timing of ice formation, as well as the stability and
smoothness of ice cover. Ice cover is also a concern with respect to transportation
capability and tailrace obstructions.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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In areas where there is inadequate protection, spilling can cause erosion and other
alterations to shorelines along spillways that may encroach on private property and place
structures at risk. Raising and lowering water levels quickly can compromise the integrity
and usefulness of docks, boat ramps, and water intake pipes.
Examples of Practices
Operations:
If the spillway channel is deemed to be fish habitat, an instream flow may be provided
during periods when there is no spill (see
Section 3.2.1). However, this may be
Sample Practices
difficult to achieve for existing facilities.
Minimum flows may be restricted to
• BC Hydro monitoring at the Hugh
periods of critical activity (migration,
Keenleyside Dam has allowed operators
spawning, egg incubation) for specific highto plan spillway gate and low-level port
value species.
operations to minimise dissolved gas
supersaturation, wherever possible.
• Manitoba Hydro’s Grand Rapids walleye
spawning research project includes
habitat enhancement in the spillway
channel and controlled spillway releases
during the spawning season.
• Ontario Power Generation controls spills
at the North Channel Spillway of the
Calabogie Generating Station to enhance
walleye spawning and protect eggs until
the end of incubation.
• Nova Scotia Power controls the increase
and decrease in spill below the Tusket
Lake Vaughan Dam during spring
migration of alewives and salmon.
A buffer zone of storage capacity can be
incorporated into the reservoir to reduce the
return period for reservoir elevations that
result in spill releases. In many cases, the
resulting spill discharge will be less than
reservoir inflows. The buffer zone is
a portion of the reservoir live storage that
is reserved for high inflow periods or
storm-induced freshets. Maintaining a buffer
zone represents a lost opportunity cost to the
hydroelectric producer, since the storage
volume may not be available during periods
of low inflow and high load.
Spill management (prespilling of small releases, spill buffering, ramping) to control the
timing and extent of water releases can maintain desirable instream conditions for fish.
This can help reduce the effects on seasonal spawning and migration requirements of
specific species.
Ramping of water flows (see Section 3.2.2) to manage their rate of change at critical times
can help support seasonal fish cycles. A gradual downramping of the spill will allow fish
to retreat from areas susceptible to dewatering and will reduce the potential for stranding.
Controlled releases from stratified reservoirs and forebays can help maintain desired water
quality and temperature. This is accomplished by releasing water simultaneously from
different zones of the reservoir or forebay.
Gas supersaturation can be reduced at some facilities through the selective use of ports
(e.g., subsurface intakes), spillways, or sluices to minimise entrainment of air and the
plunging of air and water to depth. There may be trade-offs, however, in terms of
increased wear and tear on equipment (e.g., cavitation) and erosion and other damage to
structures.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Other Measures to Minimise Effects:
Debris management by means of debris booms, stump removal, and debris catchers can
control the release of debris, vegetation, and sediment that affects water quality and
downstream habitat.
Shoreline stabilisation measures, such as the installation of riprap and the planting and
maintenance of vegetation, can reduce erosion and further sedimentation in downstream
areas. This is particularly important in the immediate vicinity of the spillway.
Manual fish salvage operations to recover stranded fish in the spillway may be required if
water control measures are not effective.
Habitat restoration (e.g., gravel replacement) or provision of alternate habitat (e.g., offchannel habitat) may be feasible and effective in areas where spawning habitat has been
reduced. Spillway channels can provide a unique setting for the creation of a controlled
habitat and hydraulic regime to attract a particular fish species at a specific time of year if
this is deemed desirable.
In cases where the spillway is immediately adjacent to the turbine discharge, it may be
desirable to optimize fish habitat in the station tailwater to attract fish away from the
spillway. Since the station has the priority for available flow, flows are typically much
more continuous in the discharge area than in the spillway.
Where habitat restoration is not practical or useful, stocking may be effective to support
affected fish populations.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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3.2.4 Synchronous Condensing Operations
Description
Synchronous condensing operations are designed for voltage regulation of the
transmission system. They also provide the benefit of allowing a unit to revert quickly to
a generating mode, thereby reducing turbine wear and tear and delays in energy supply.
This operating mode is only used for certain generating units where system stability is
required. Synchronous condensing operations can be provided by either thermal or
hydroelectric facilities.
Under synchronous condensing operations, the wicket gate is closed, preventing water
from passing through the turbine. In most units, air is then forced under pressure into the
turbine chamber to displace any remaining water. The turbine continues to spin in air,
basically functioning as a motor and regulating voltage by either supplying or absorbing
power, as needed by the system.
Since the wicket gate seals are often imperfect, there is generally some water leakage into
the turbine chamber. Due to pressure differentials between the penstock, turbine
chamber, the scroll case, and the draft tube, the leaked water under elevated air pressure
may become supersaturated with dissolved nitrogen and oxygen gases. Once this water
enters the tailrace, gas saturation levels can exceed 110 percent. The extent of
supersaturation typically varies with the pressure in the scroll case, as well as the amount
of time during which the air and water are in contact.
Fish and Fish Habitat Effects
The extent of oxygen saturation in the tailrace will depend largely on the operation of the
facility. In many generating stations, there will be some units that are running in
generating mode and others in synchronous condensing mode. In these facilities, the
amount of leakage through a unit operating in synchronous condensing mode would be
very small compared to the amount of discharge through the units running in generation
mode. In this case, dilution by water from the operating turbine(s) would eliminate the
negative impact of elevated gases. In a situation where units are operated in synchronous
condensing mode with no dilution, it is possible to flush the tailrace on a periodic basis to
dilute any elevated gas-bearing water.
Dissolved gas supersaturation has been shown to have adverse physiological effects on
fish and invertebrates. Exposure to high gas saturation levels (i.e., 110% and greater) can
cause fish to exhibit signs of bubble trauma gas (BTG). Internal bubbles may form in the
bloodstream and tissues, disrupting neurological, cardiovascular, respiratory,
osmoregulatory, and other functions. Depending on the length and level of DGS
exposure, fish mortality may result.
Gas bubble trauma in fish may also contribute indirectly to fish mortality. Fish tend to be
weakened by exposure, particularly in juvenile life stages. The ability of the fish to avoid
predators can be impaired. GBT may also increase the susceptibility of fish to other
stresses, such as bacterial, viral, and fungal infections.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Much less is known about fish mortality and impairment from GBT exposure in actual
rivers and streams than in a laboratory environment. Free-swimming fish may avoid DGS
by swimming in deeper levels where water pressure compensates for high gas saturation.
However, recent monitoring by BC Hydro suggests that higher gas saturation levels do not
necessarily deter adult rainbow trout from their normal surface feeding behaviour.
Juvenile fish may experience greater exposure through daily feeding in shallow waters,
and may be more vulnerable to increased predation. Migrating salmonids receive
fluctuating levels of exposure, the overall debilitating effects are being assessed through
collaborative research.
Other Considerations
The production of high gas saturation levels by synchronous condensing operations is
dependent on the quality of the gate seals, as well as other turbine design parameters.
Saturation levels will also depend on how many turbines are operating in synchronous
condensing mode and the duration of that operation, as well as the dilution of saturated
water by other generating units at the facility.
Water temperature is inherently related to the level of dissolved gas in the water. The
higher the temperature the greater is the amount of gas remaining in solution. It is also
possible that elevated water temperatures and elevated gas levels act synergistically to
impact aquatic biota.
Examples of Practices
Operations:
Flushing flows may be provided by
periodically opening up the gates to flush
the system and dilute the build-up of
supersaturated water from the tailrace.
This avoids DGS effects on fish residing
in the tailwaters or in manifolds. The
frequency of this practice depends on,
among other things, the gas saturation
levels produced and seasonal
considerations (i.e., the presence of
migratory fish in the tailrace or manifolds).
Sample Practices
• BC Hydro monitored gas saturation levels
at the Mica Dam, and implemented an
operation that took the units off of
synchronous condensing mode at regular
intervals to flush supersaturated water out
of the manifold/tailrace and thus reduce
impacts on fish.
Other Measures to Minimise Effects:
Monitoring to assess gas saturation under a range of operating conditions can assist in
operations planning to mitigate DGS impacts.
Field studies documenting the impacts of elevated gas levels on fish in riverine systems are
extremely complex to carry out, but have been undertaken. Further laboratory study will
also serve to increase understanding of the impacts of gas supersaturation on aquatic biota.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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3.3
DAMS AND FISH MOVEMENT
The hydroelectric facilities in Canada were constructed many decades ago in accordance
with regulatory requirements and decision-making processes at the time. Where
opportunities exist to make improvements to existing facilities to enhance fish passage,
utilities will work co-operatively with regulatory agencies to explore these opportunities as
part of environmental stewardship. This practices document on hydroelectric operations
demonstrates utilities’ commitment towards environmental stewardship and sound
management practices.
3.3.1 Migratory Species
Description
Hydroelectric dams create barriers that can prevent or impede fish movement upstream
and downstream of a facility. This is most important when migratory species such as
salmon no longer have access to critical habitat for reproduction with the possible loss of
the stock or a significant decrease in yield to a fishery. Fish passage methods or fish
passageways may be used in certain instances to direct fish around, over, or through the
dam.
At new hydroelectric stations or dams, requirements for fish passage are determined at the
time of facility construction and licensing. At new facilities the utility has the advantage
of incorporating such requirements into the design of the station.
Retrofitting fish passage to existing stations or dams for which fish passage was not
originally prescribed can be difficult, expensive, or even impractical. As fish passage is
species- and site-specific, the existing design of hydroelectric facilities can prohibit the
design and construction of effective passage. If the facility was built on natural barriers
(e.g. waterfalls) or if the facility was constructed as part of a diversion system in which the
use of fish passage may divert fish species to another river system, retrofitting the facility
with fish passage may not be desirable. Alternatives to passage include enhancement
measures, hatcheries, and spawning channels, and may be used to compensate for loss of
spawning habitat or access to habitat.
Consequently, the need and feasibility of fish passage at existing sites is determined on a
facility by facility basis. Decisions regarding fish passage are influenced by past practices,
existing agreements, the perceived social value of the fish, the economic or cultural
significance of the fishery, the presence of adjacent key habitat, water quality, risks to fish
populations, and other competing water uses and considerations. Generally, fish passage
has been associated more with coastal areas or large lakes characterised by large stocks of
valuable migratory species than with inland areas of the country.
Passage measures may be active or passive in nature, and may involve attracting and/or
repelling mechanisms. Different systems would normally be used for upstream and
downstream passage. Upstream Passage is usually directed at moving migrating adult fish
upstream around the dam or barrier, but may also refer to the movement of young elvers
upstream. Downstream Passage is focused on bypassing juveniles or spent adult spawners
downstream around a barrier.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Fish and Fish Habitat Effects
Hydroelectric dams can block migratory fish species from accessing critical upstream
habitat for spawning and rearing. Migrating fish have innate homing cues that may be
altered with the existence of a dam. If migration is significantly delayed or prevented,
then spawning activity can be reduced or eliminated, with obvious long-term implications
for stock recruitment. Upstream fish passage tends to be focused on coastal migratory
species, including chum, sockeye salmon, Atlantic salmon, sea run trout, blueback
herring, alewife, American eel, and American shad.
Downstream migration is important for seaward-migrating juvenile fish, spent adults, or
mature eels. Without proper downstream bypasses, fish are directed through the turbines
or over spillways, at times resulting in injury or mortality from physical strikes, cavitation,
sheer stresses, or severe pressure changes. Fish that survive the passage may also be
vulnerable to the effects of water quality impacts, notably turbidity and gas
supersaturation. Such vulnerability may put them at risk from predation by birds, fish, and
other predators.
In making decisions regarding fish passage systems, it is important to consider several
characteristics related to specific species or stocks, including:
•
•
•
•
•
•
whether the fish are migrating or resident
species-to-species interactions
lifecycle stage
swimming and leaping performance
access to critical habitat
socio-economic value of the species.
Other Considerations
Other key considerations for retrofitting fish passage systems at existing facilities are the
facility age and the configuration and basic design of hydroelectric structures and
equipment. Upstream of the dam, headponds and reservoirs, especially in smaller
hydroelectric systems, may have caused significant alteration of habitat (i.e., changing the
area from riverine to lacustrine habitat). If the river has been developed as a cascade
system with multiple dams and headponds, the cumulative effects on habitat may
preclude any further consideration of fish passage.
The feasibility of upstream passage may also be affected by physical limitations (e.g., dam
height, a lack of space for new facilities), the availability of water (since passage facilities
require water to operate the ladder and attract fish to the entrance), recreational water
uses, and other factors.
The feasibility or design of downstream passage can be affected by physical limitations
(e.g., the inherent design of existing facilities), debris loading, seasonal water availability,
public safety concerns, and turbine characteristics (blade size, clearances, rotational
speed, cavitation).
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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For existing facilities in general, decisions on fish passage may also be affected by
prevailing agreements and approvals, flood control considerations, recreational use, and
other power system commitments.
Examples of Practices
Although most dams do not have fish
passage facilities, a number of methods for
accomplishing this task have been
developed over time. As the effectiveness
and feasibility of these options is highly
dependent on the location and
configuration of the dam and the existence
of notable migratory species, these options
must be assessed on a site-by site basis.
Some of the options outlined below have
been applied at Canadian hydroelectric
facilities.
Mitigation (Upstream):
Sample Practices
• Hydro-Quebec has been operating
an eel ladder at the Chambly Dam
since 1997.
• A fish passageway at New Brunswick
Power’s Mactaquac Generating Station
allowed measurement of the passage
efficiency of two other facilities where
operational improvements have since
been made.
• Nova Scotia Power operates a diversion
screen on the Black River system to
divert downstream migrating juvenile
alewives away from 4 of 5 stations on the
system.
• At the Puntledge Dam, BC Hydro
installed state-of-the-art fish screens so
that today 99% of the migrating juvenile
salmon and steelhead survive their
journey past the facility.
Fish ladders or fishways reduce water
velocity and gradient so that fish can
ascend and pass the dam in manageable
steps. They consist of an entrance, a fish
passage (a series of sloping channels with
pools provided by weirs or baffles), an exit,
and an auxiliary water supply (which is
often used to provide attraction water). There are several basic designs that have
been adopted in North America:
• Pool-and-weir systems are the simplest form of fish ladder, best suited to
streams with minimal fluctuation in water level (e.g., streams regulated by
relatively large lakes or dams).
• The Ice Harbour ladder is similar to the pool-and-weir, with a design difference
in the number and location of the slots.
• Vertical slot and Denil systems use passages with baffles, and work well in
streams with fluctuating water levels and steep slopes, respectively.
• Eel ladders are specialised high-gradient ladders that have been developed to
facilitate the upstream movement of juvenile eels at a few generating stations
in Quebec and Ontario.
In fish locks and fish lifts/elevators, fish are attracted or crowded into a lock chamber,
raised above the dam by filling the chamber with water, and released over the dam. A lift
or elevator system requires a fish collection facility near the tailrace with a fish entrance, a
V trap, and a crowding device to force fish into a water-filled hopper. Fish are then lifted
to the forebay level and released. The fish may be trucked to a location immediately
upstream or to areas more remote from the trap.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Barriers may be used in conjunction with the above passage equipment to direct fish
toward or away from critical areas, thereby making the equipment more effective. A
variety of physical and behavioural barriers may be employed, such as bar racks, louver
diversion systems, diversion screens, strobe lights, sound, and electric fields.
Operations (Downstream Passage Improvements):
Operating turbines near maximum efficiency can reduce fish injury and mortality from
entrainment, although survival rate is variable, depending on the size of the fish relative
to the size of the turbines. Turbines of recent design have fish passage efficiencies greater
than 85 percent in certain circumstances, due to improved blade and wicket gate
clearances and reduced pressure changes. In certain instances, utilities are able to
replace runners within the turbine to obtain better energy efficiency and reduce impacts
on fish passage.
At some facilities, deliberate spilling has been used, or the plant has been operated at a
specific load, to move fish through or around the facility. For example, at the six unit
Mactaquac Generating Station on the Saint John River in New Brunswick, it has been
noted that fish migrating downstream tend to congregate in one area of the forebay,
closest to the shoreline. When fish are seen congregating in that location, the Station
attempts to operate its units at near maximum efficiency to assist moving the fish
downstream. On occasion, scheduled maintenance shutdowns of generating units may
be planned to coincide with peak migration periods.
Downstream Mitigation:
Behavioural barriers have been developed and used in some instances to alter or take
advantage of natural behaviour patterns in order to attract or repel fish. The potential
advantages of behavioural devices are their relatively lower cost. Measures include strobe
lights, filtered mercury vapour lights, air bubble curtains, low frequency sound,
infrasound, electric screens, water jet curtains, hanging chain or rope barriers, chemicals,
visual keys, or hybrid behavioural devices (e.g., sound as a repellant from one area
combined with light as an attractant to a nearby site). Practical applications show that the
success of behavioural devices varies significantly with species, life stage, and particular
site considerations.
Physical barriers may be used when there is uncertainty as to the effectiveness of
behavioural devices alone, or where such devices are not practical. Among these barriers
are infiltration intakes, porous dikes, cylindrical wedge-wire screens, barrier nets, bar
racks, and travelling and fixed screens. Where other passage equipment has been
provided (e.g., fish locks and lifts), screens may be employed to prevent fish passage
through turbines and over spillways. Travelling screens may be installed at larger
hydroelectric facilities with higher water flows, while fixed screens may be used more for
smaller facilities.
Conventional travelling screens have been modified to incorporate changes that improve
fish survival. In some cases, they are used as collection systems, with bucket attachments
to collect the fish. The fish are subsequently released in a safe location. Fish pumps are
also used in some cases for collection purposes.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 49
Diversion systems are the primary component of any downstream passageway. Significant
work has been done in recent years to design systems that function under a range of
conditions, and that can withstand the pressures exerted by debris and other confounding
items. Some of the diversion measures in existence include:
• angled rotary drum screens, which were used more commonly in the past
and now tend to be replaced by flat-panelled designs.
• vertical devices, such as louvers (arrays of evenly spaced, vertical slats aligned
across a channel at a specified angle and leading to a bypass) and angled
screens or walls (requiring relatively uniform flow conditions, a fairly constant
approach velocity, and a low through-screen velocity) and
• horizontal devices, such as inclined plane screens (designed to divert fish up
into the water column), eicher screens [an improved design on the original
inclined plane screen, suitable for use in high-velocity (10 fps) water flows],
modular inclined screens [an entrance with trash racks, dewatering stop logs
in slots, an inclined screen set at a shallow (10 to 20 degree) angle to the flow,
and a bypass for directing diverted fish to a transport pipe], and Nu-Alden
weirs (with a contoured entrance and sloping bottom to avoid rapid
acceleration in flow).
• submerged travelling screens, which are used for high-head conditions.
3.3.2 Non-migratory Resident Species
Description
The vast majority of hydroelectric dams in Canada have no provision for fish passage.
This is especially true for inland waters where the resident fish species (e.g., smallmouth
bass, walleye, brook trout, lake sturgeon, pike, and perch) can survive and reproduce
without undertaking extensive migrations. However, fish passage may be considered if
accidental entrainment through dams or stations, or fragmentation of the river habitat by
dams threatens stocks. In this case, the emphasis is on preventing the entrainment of
upstream fish rather than collecting and passing them downstream.
Fish and Fish Habitat Effects
Accidental entrainment probably occurs from time to time at all dams and generating
stations when reservoir fish come into contact with the upstream current field from intakes
or spillways. The ability of a fish to escape entrainment will be a function of its size and
swimming capability. Trash racks may prevent large fish from passing through a station
intake although they may be impinged on the racks. The degree of fish mortality as they
pass through the dam or station depends on the species and size of the fish (generally the
smaller the fish, the lower the rate of mortality).
The rate of entrainment may be very low at older stations where chronic entrainment over
many years has eliminated the local population near the intake or spillway. At other sites,
the rate of entrainment may remain high decades after construction if population pressure
in the reservoir leads to a downstream dispersal of surplus population.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
The net effect of chronic accidental entrainment is to pass a portion of the upstream
population to the population downstream of the dam with a certain degree of mortality
occurring during the transfer. If intraspecific competition in the downstream population is
high, there may be no additional yield to the downstream fishery; however, entrainment
may partly explain the high fishery yields that often occur downstream of dams. Even if
there is no net increase in yield in the downstream population, there will be a transfer of
genetic material from the upstream to the downstream population (semi-isolated stocks).
If entrainment occurs at a diversion dam where there is no downstream compensatory
flow, there could be stranding.
The impact of accidental entrainment on upstream populations is not well understood.
There are no documented cases in Canada where an upstream stock of a resident species
has been eliminated by accidental entrainment although this may be an artifact of poor
pre-project environmental information at older stations. Accidental entrainment could
theoretically reduce yields to an upstream fishery, but this is often not evident for larger
reservoirs where stock assessments have been done.
Fragmentation is the cumulative division of habitat into ever smaller parts until it becomes
too small to support a species or stock. Many rivers in Canada are naturally fragmented
by waterfalls and rapids, especially on the Canadian Shield and in the mountainous
regions of the country Such natural barriers often become the sites for hydroelectric
projects in inland areas. These rivers have been colonized by fish species that can
complete their whole life cycle within a reach of river. They exist as a series of semiisolated populations where individuals and genetic material can pass downstream through
barriers but not upstream.
The construction of several dams on a river may substantially increase fragmentation of
habitat and may negatively affect some species of fish. This may be especially true for
cascade developments where much of the river has been converted to a series of dams
and headponds, and only the tailwaters of the stations and spillways provide riverine-type
habitat. In this case, riverine species will be at most risk to fragmentation.
There are some circumstances where the maintenance of species separation by dams is
desirable. Examples include the need to restrict marine lamprey movement from the Great
Lakes to its tributaries, to isolate cage/hatchery fish from native species, and to separate
introduced species (e.g., bass) from native species (e.g., trout).
Other Considerations
Other considerations are basically the same as those presented in the preceding section
on migratory species. The feasibility or design of entrainment barriers can be affected by
physical limitations (e.g., the inherent design of existing facilities), debris loading, seasonal
water availability, and public safety concerns. Turbine characteristics (blade size,
clearances, rotational speed, cavitation) and station operational efficiency will affect the
survival rate of entrained fish.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 51
Examples of Practices
Operating turbines near maximum
efficiency can reduce fish injury and
mortality during entrainment. Turbines of
recent design have fish passage efficiencies
greater than 85 percent in certain
circumstances, due to improved blade and
wicket gate clearances and reduced
pressure changes. It is generally not
possible to retrofit fish-friendly turbines to
existing stations unless the stations are
completely redeveloped. In certain
instances, however, utilities are able to
replace runners within the turbine to
obtain better energy efficiency and reduce
impacts on fish passage.
Sample Practices
• OPG spills surplus water each spring
at the Little Long Control Structure on
the lower Mattagami River. After the
spill is complete and the gates
closed, mature lake sturgeon are
salvaged from pools downstream of
the Control Structure and returned to
the Little Long Reservoir. Research is
being conducted on behavioural
systems to divert sturgeon from the
Control Structure during the spill.
• Manitoba Hydro is involved in a
model fishway project to measure the
swimming performance of walleye,
smallmouth bass, and other native
species.
If accidental entrainment is significant,
physical and behavioural barriers can be
retrofitted to intakes and spillways. These have been discussed in detail in the preceding
section on migratory species - downstream mitigation.
There are no cases in Canada where upstream passage has been developed to solve a
habitat fragmentation issue.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.4
PUMPED STORAGE
Description
There is only one pumped storage generating facility in Canada: Ontario Power
Generation’s 174 MW Sir Adam Beck Pump Generation Station at Niagara Falls.
Outside Canada, pumped storage is usually a complementary project for thermal power.
All pumped storage plants rely on being able to purchase inexpensive off-peak power
generated by base-loaded generating stations (e.g., Sir Adam Beck 1 and 2 Generating
Stations on the Niagara River) that continue to run in off-peak periods of the day or week.
They use this energy to pump water back up into the reservoir from which they draw
when in generating mode. Pumping usually takes place on a seven-day cycle to enable a
five-day generation cycle during on-peak periods. The major reason for this difference in
cycle is that the efficiency of pumping is not as great as that of generation, so that it takes
longer to pump the water required to fill the reservoir.
Fish and Fish Habitat Effects
The main area of concern with regard to a pumped storage operation is the risk of fish
becoming entrained when the plant is pumping water from the lake or river up into the
storage reservoir.
Other Considerations
Notice must be provided to the boating community to reduce the risk of watercraft
becoming entangled in the protective netting or screening that prevents fish from being
taken up in the pumping mode.
There will be a need to address the issue of species transfer if the system is not a closed
loop. Unwanted species, such as zebra mussels or lamprey eels, must be prevented from
moving from impacted areas to areas that have not been affected.
Examples of Practices
The practices that can be employed to reduce fish impacts are similar to those for
enabling downstream fish passage (see Section 3.3 on Dams and Fish Movement).
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 53
3.5
MAINTENANCE PRACTICES
3.5.1 Routine Maintenance
Routine maintenance activities take place at all major industrial facilities, including
hydroelectric generating stations. The manner in which these activities are carried out
depends on a number of factors, including the health and safety of employees and the
public, the timing of energy demand and production requirements, the choice of
maintenance materials and methods to be used, and the site or area where the work is to
be conducted. Federal or provincial regulations, guidelines, or codes of practice cover
many routine activities. This section reviews the key issues related to routine
maintenance activities that have potential implications for fish and fish habitat.
Routine activities are defined as those activities that are an essential ongoing requirement
to support the operation of a hydroelectric facility. Typically, such activities occur on a
regular basis – for example, daily plant checks, yearly transformer oil sampling, monthly
motor maintenance, and annual vegetation maintenance – and extend over the life of
the facility.
Description
Routine activities that are undertaken at hydroelectric facilities include:
• maintenance of operating equipment, involving the management of oils, fuels,
chemicals, and waste from these activities
• maintenance of facility structures, involving cleaning (e.g., floor washing,
sandblasting), painting, and minor concrete repair work
• management of vegetation in and around structures (e.g., dams, electrical
switchyards, transmission line right of ways)
• work in and around watercourses to stabilise banks, control erosion, maintain
transmission corridors, and maintain public access points (e.g., boat ramps).
What differentiates these activities at a hydroelectric facility from similar activities at other
industrial facilities is the proximity to and possible interaction with the watercourse. This
potential interaction, and the negative impacts it may have on the public, fish and fish
habitat, and other water users, means that extreme care must be taken in planning and
implementing the work.
Fish and Fish Habitat Effects
The routine activities noted above all have the potential for causing or creating a discharge
of material into the watercourse and, thus, for potentially impacting fish and their habitat.
For example, some chemicals (e.g., paints, solvents) can lead to changes in water chemistry
that degrade habitat, although the effects are usually localised and short-term in duration
due to high dilution rates. Without proper management practices, sandblasting can
introduce particles that affect water quality (i.e., increase turbidity) and smother spawning
areas. However, the use of standard work practices, as currently legislated, typically
ensures that these environmental effects are properly managed and kept to a minimum.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Other Considerations
Private property and infrastructure can be a consideration for erosion control and
shoreline maintenance in areas downstream of facility structures. The maintenance
methods and materials used are often affected by how an adjacent landowner wishes to
use the foreshore. Work may have to be done when access is possible, for example, when
the ground is drier, or a field is not being farmed.
In addition, many of these activities are covered by legislation or permit requirements.
In such cases, the regulatory regime may dictate when or how work is to be carried out.
There may also be public safety concerns, such that the maintenance techniques are
defined by health and safety requirements. For example, some pesticides used for
vegetation management require a “no contact” period after application. As a result, work
may be scheduled to avoid conflicts with recreationists and other resource users.
Examples of Practices
Operations:
Routine activities requiring the use of chemicals, oils, fuels, or similar materials with
potentially negative environment effects are typically identified and managed through
policies and procedures, training and, in some instances, physical monitoring systems
and controls. These management measures apply to activities that involve the use of
pesticides for vegetation control, diesel or gasoline in maintenance equipment, and
insulating or lubricating oils in operating equipment. Many such activities, including
pesticide use, are also covered by legislation.
For activities related to the maintenance of structures (e.g., painting, light concrete work),
care must be exercised to ensure that the choice of materials takes into account possible
impacts on the environment. For example, there are many different abrasives that can be
used for sandblasting, some of which carry fewer environmental effects. In addition, in
contrast to a decade ago, most jurisdictions now require that sandblasting materials be
collected and not released into the environment at all.
Provincial permitting requirements generally cover routine activities around watercourses.
These activities should be planned to minimise the direct disturbance of banks, and to
ensure that the work does not lead to further erosion. Activities are best done with careful
and detailed engineering. For example, when planning a temporary or permanent access
road across a tributary stream, several engineering factors must be considered: whether to
construct a ford or a bridge; what size of structure is required; the method and scheduling
of construction; and the need for use restrictions.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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Other Measures to Minimise Effects:
Mitigation of negative impacts can be achieved through careful planning of routine
maintenance activities, combined with close monitoring of the activities as they are
carried out. An example in the case of fuel use is the proper design of fuel storage
facilities, including secondary containment if required, together with regular monitoring of
use to check for leakage. To mitigate against impacts in the event of a fuel, chemical, or
oil spill, the facility should have an emergency response plan in place. This plan can vary
in scope from the facility having its own response capability (trained personnel and
related equipment) to simply knowing whom to call for assistance in the event of a spill.
For work around watercourses, careful planning is the first mitigation strategy. This
requires planning the maintenance activity (e.g., bank stabilisation) in accordance with
applicable regulations and guidelines, ensuring that protection measures (e.g., silt
curtains) are implemented prior to start-up, and conducting regular inspections during
the work to ensure that no soil or other erodible material enters the watercourse.
If the maintenance activity results in a significant loss of habitat or other environmental
effect, various kinds of compensation can be considered. For example, new habitat can
be created in another location. Alternatively, the hydroelectric producer may provide
funds to support local fish enhancement projects.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
3.5.2 Facilities Repair and Rehabilitation Activities
Description
During the life of a hydroelectric generating station, there are occasionally requirements
to conduct “non-routine” maintenance. This work may be defined as maintenance that is
anticipated at time of planning, but that may occur only a few times over the facility’s life.
Types of work that might be considered in this category include:
• major concrete or structural repairs, such as rebuilding a spillway or control
gate structure
• channel improvements to improve tailwater hydraulics and optimize head
• blasting and dredging to enable channel improvements, control sedimentation,
and remove other obstructions (e.g., to fish passage) that develop during
facility operation
• bank stabilisation and other measures to control the effects of ongoing erosion.
Fish and Fish Habitat Effects
Given the potential size and complexity of these non-routine maintenance activities, the
fish and habitat impacts that may result depend largely on how the work area is managed.
For example, will the area be dewatered or will the work be performed “in the wet”? Will
fish be physically removed or will they be left in the area?
If the area is dewatered prior to undertaking the work, fish may be affected by the
construction of a dam or berm to keep water out. This structure itself can cause loss of
fish habitat or limit fish passage. If the area is dewatered and fish must be removed, then
they may experience trauma and other physical effects.
For work that is carried out without dewatering the area, including bank stabilisation and
in-situ blasting and dredging, impacts may be related to the direct loss of habitat (e.g.,
spawning substrate) or degradation of water quality from the creation of suspended solids.
On the other hand, some erosion control measures, such as large diameter rip rap and
tree planting, can create fish habitat and refuge. Similarly, blasting can create new loose
substrate for spawning, or may provide access to a previously blocked tributary stream.
Other Considerations
Generally, major repair and rehabilitation projects are covered under provincial or federal
legislation and require regulatory approvals. For example, blasting carried out in a
watercourse should be conducted according to Fisheries and Oceans Canada’s Guidelines
for Use of Explosives in or near Canadian Fisheries Waters (Canadian Technical Report of
Fisheries and Aquatic Sciences 2107, Wright, D.G., and Hopky, G.E. DFO 1998).
Dredging is subject to regulation under federal legislation, including the Navigable Waters
Protection Act and Canadian Environmental Protection Act.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 57
Facility-related constraints, such as the area topography and proximity to dams and other
manmade structures, may limit the need for or feasibility of certain activities, such as
dredging and blasting.
Since major repair activities are often highly visible, they may affect recreational activities
and other key uses of the watercourse. Therefore, the planning of these activities must
recognise the needs of other users, while following applicable legislation and guidelines.
Examples of Practices
Operations:
The regulatory approvals required for facility repair and rehabilitation projects often
include conditions under which the work must be carried out. These may include
limitations on when the work can be conducted, reflecting the sensitivity of different fish
species, and the types of materials and equipment that can be used. For example,
approvals may prohibit the use of explosives unless a blasting plan is prepared and
approved, or may require “ripping” the rock with heavy equipment, if feasible, as an
alternative to blasting.
For work in the watercourse, consideration should be given to using a small “avoidance”
blast to drive fish away from the impact area before the main blast is detonated, or before
major dredging takes place. In addition, the work area may be closed off with nets and
fish may be removed from the blast area through electrofishing or netting. Similarly, in
sensitive fisheries areas, a bubble curtain or comparable system may be used to surround
the work site, in order to control fish movement, minimise the dispersion of suspended
solids, and reduce the blast’s shockwave impact.
Other Measures to Minimise Effects:
Mitigation is best carried out through effective planning and ensuring that the
maintenance work meets guidelines and approvals, with input, as required, from the
appropriate regulatory agencies.
Once the onsite work commences, regular inspections should be undertaken to ensure
that operation and mitigation measures are working and to make any necessary
adjustments.
In the case of erosion control, measures may include the installation of rip rap or armour
rock, the creation of protected natural buffer zones, vegetation management, and longterm erosion monitoring.
Where the impacts of non-routine activities cannot be avoided, habitat enhancement, fish
restocking, and other compensation measures may be used to address any negative
impacts on fish and fish habitat.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
APPENDIX A: PROVINCIAL LEGISLATION AND REGULATIONS
An extensive regulatory framework governing the operations of hydroelectric generation
facilities exists at the provincial level.
Environmental assessments (EAs) are generally the first level of environmental approval,
since the intent of the EA process is to ensure that the environmental effects of projects are
considered early in the planning process. However, most of the hydroelectric facilities in
Canada were constructed prior to the development of environmental assessment
legislation, and their operations are exempt from such requirements. Depending on the
nature of reconstruction and rehabilitation, an EA may be needed. Where assessments are
required at both the federal and provincial levels, initiatives to harmonise the EA
processes between the two levels are used.
There are numerous provincial acts regarding environmental protection and management
that are relevant to the day-to-day operation of hydroelectric facilities. Table A.1 provides
a snapshot of some key legislation by category and province.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Water Act
Fisheries Renewal Act
Wildlife Act
Ecological Reserved Act
Yukon Waters Act
Yukon River and Alsek River
Basin Agreements Act
Civil Emergency Measures Act
An Act Approving Yukon Land
Claims Final Agreements
Water Act
Electric Energy Act
Water Power Act
Water Corporation Act
Water Power Act
Water Rights Act
Ontario Water Resources Act
Lakes and Rivers
Improvements Act
Watercourses Act
Clean Water Act
Environment Act
Water Protection Act
British Columbia
Yukon
Alberta
Saskatchewan
Manitoba
Ontario
Quebec
New Brunswick
Nova Scotia
Newfoundland
Water Control
Wilderness and Ecological
Reserves Act
Fisheries and Coastal Resources Act
Resources Act
Wildlife Act
Endangered Species Act
Special Places Protection Act
Marshland Reclamation Act
Fish and Wildlife Act
Endangered Species Act
Ecological Reserves Act
Ecological Reserves Act
Endangered Species Act
Gasoline-Handling Act & Code
Transportation of Dangerous
Goods Act
Wildlife Act
Endangered Species Act
Fisheries Act (Provincial)
Wildlife Act
Wildlife Act
Wildlife Act
Freshwater Fisheries Agreement
Act
An Act Approving Yukon Land
Claims Final Agreements
Fish Protection Act
Fish and Wildlife/
Ecological Protection
Environment Act
Petroleum Products and
Equipment Act
Pesticides Act
Environmental Protection Act
Dangerous Goods Handling and
Transportation Act
Environmental Management and
Protection Act
Dangerous Goods Handling and
Transportation Act
Occupational Health and Safety
Act
Weed Control Act
Safety Codes Act, Fire Code
Dangerous Goods Transportation
Act
Public Health Act
Waste Management Act
Pollution Control/
Waste Management
Environmental Assessment Act
Environment Act
Environment Act
Clean Environment Act
Environmental Quality Act
Environmental Assessment Act
Environment Act
Environmental Assessment Act
Environmental Protection and
Enhancement Act
Public lands Act
Forest and Prairie Protection Act
An Act Approving Yukon Land
Claims Final Agreements
Forest Protection Act
Historic Resources Act
Land Planning and Development
Act
Lands Act
Parks Act
Environmental Assessment Act
Other Environmental
Legislation
Table A.1: Provincial Environmental Legislation Relevant to Hydroelectric Operations
APPENDIX B: GLOSSARY
Anoxia/Anoxic
Oxygen-deprivation; a condition where increased nutrient
consumption leads to decreased concentration of disolved
oxygen in the water.
Base Load
The minimum load in a power system over a given period
of time.
Base Load Plant
A generation facility that runs continuously except during
maintenance and outages.
Benthos
The aggregate of organisms living on or at the bottom of a
body of water.
Block Loading
Part of the base load operation of a facility designed to
respond to fluctuating seasonal demand.
Cascading System
A sequence of hydroelectric facilities along the same
watercourse, where the outflow from one facility flows
directly into the reservoir of the next.
Channel
A long, deep portion of a river or other waterway through
which water and sediment flow.
Dam
A structure built as a barrier to the flow of a stream or river.
Also refers to the act of impeding the flow of a watercourse.
Dissolved Gas
Supersaturation (DGS)
Water characteristic that results when solutions of dissolved
gases (e.g., nitrogen and oxygen) exceed the saturation level
of the water (greater than 100 percent).
Diversion
The taking of water from a stream or other water body into a
canal, pipe, or other conduit
Draft Tube
The discharge tube leading from the turbine to the tailrace.
Drawdown
The difference between maximum and minimum water
levels in a reservoir. Also refers to the act of lowering
reservoir levels.
Entrainment
The process by which fish are swept into and through
spillways and turbines; may result in injury and fish
mortality.
Fish Ladder
A series of pools arranged like steps which fish can use to
pass upstream over a dam.
Fish Lift
A device similar to an elevator within which fish are
transported over a hydroelectric facility and deposited in the
upstream reservoir.
Flood
A natural and generally short-term rise of a stream or river
above its normal level resulting from rainfall or snowmelt.
Floodplain
The land area of a river valley that becomes inundated with
water during a flood.
Flow
The rate at which water passes a given point in a stream or
river, usually expressed in cubic metres per second (cms).
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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Flow Management
The management of hydroelectric operations to
reconcile/control downstream water flows and their various
effects.
Flow Regime
A range of possible flow levels or conditions in a
watercourse.
Flushing Flow
A short pulse of high water flow used to clear silt, condition
spawning substrates, and in some cases encourage fish
migration.
Forebay
The section of the reservoir that is immediately upstream
from the powerhouse.
Francis turbine
A radial inflow reaction turbine.
Freshet
A high river flow in the spring caused by rapid snowmelt.
Head
The difference in elevation between water levels upstream
and downstream of a dam.
Headwaters
Streams at the source of a river.
Head Pond
The reservoir behind a run-of-river dam.
High Flow
The periodic increase in a river’s water level as result of
increased precipitation or snowmelt.
Hydrograph
A graph showing the water level, discharge, or other
property of river volume with respect to time. For example,
an annual hydrograph charts the varying river levels over
the course of a year.
Hydrology/Hydrologic Cycle The applied science concerned with the waters of the earth,
their occurrences, distribution, and circulation through the
continuous hydrologic cycle of evaporation, transpiration,
precipitation, infiltration, storage, and runoff.
Impoundment
A body of water formed behind a dam.
Instream/Fish Flow
Artificially increased flow in the river system for fish and
fish habitat, recreation, or another water use requirement.
Intake
The entrance to a conduit through a dam or water facility.
Kaplan turbine
An axial flow reaction turbine with adjustable runner blades
which is used mainly under low head conditions.
Lacustrine
Of, pertaining to, or inhabiting lakes.
Littoral
Of or pertaining to the shallow zone of a lake or river in
which light penetrates to the bottom, permitting plant growth.
Live Storage
The volume of water in a reservoir that can be used for
power generation or other purposes, which is generally less
than the storage capacity.
Low Flow
The periodic natural decline in a river’s water level as result
of reduced precipitation.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Mainstem
The unimpeded, main channel of a river, as opposed to the
streams that feed into it.
Maximum Operating Level
The highest level to which water in a reservoir can rise
under normal operating conditions.
Minimum flow
The minimum water flow required to sustain aquatic life in
a river or stream.
Peak Load
The maximum load in a power system over a given period
of time.
Peaking Plant
A generation facility normal designed for use only during
peak loads.
Penstock
The pipeline that carries water from the reservoir to the
turbine.
Ponding
The formation of a reservoir due to the damming of a creek
or river. Also refers to raising the water level of an existing
reservoir.
Ramping
The operational process of gradually increasing generation
and flow discharges (upramping) or decreasing generation
and flow discharges (downramping) to smooth variation in
water flows.
Regulated River
A river of which the natural flow regime is altered by a dam
or dams.
Regulating Gates
Gates that control the amount of water flowing out of a
reservoir and down to the turbines of a generating facility.
Release
The volume of water allowed to flow out of a reservoir.
Reservoir
A body of water collected and stored behind a dam, usually
in the form of an artificial lake.
Resident species
Fish that spend their entire life cycle in freshwater.
Riprap
A streambank protection method using large rocks,
boulders, or debris to reduce erosion.
Riparian
Along the banks of streams, lakes, or rivers.
Riverine
Of, pertaining to, or inhabiting rivers.
Rule Curve
A graphic guide to the use of storage water used to define
operating constraints for a reservoir.
Run-of-River
A hydroelectric facility that has no upstream storage
capacity and so must pass all water flows as they come.
Scroll Case
A spiral-shaped steel intake guiding the flow of water into
the turbine wicket gate.
Spill
Water passed over a dam without going through the
turbine(s) to produce electricity.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
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Spillway
The channel or passageway around or over a dam through
which excess water is released or spilled without passing
through the turbines; a safety valve for the dam.
Storage
The total volume of water upstream of a generating station
or water control structure (dam) at any given point in time.
Storage Capacity
The volume of water contained between the maximum and
minimum allowable levels within a reservoir.
Storage Reservoir
A reservoir with space for retaining water (e.g., from the
spring snowmelt) to be released for power generation and
other uses.
Tailrace
A pipe or channel through which water from a turbine is
discharged into a river.
Thermal Stratification
The segmentation of deep reservoirs into zones of warmer
and cooler water, which can occur during the summer.
Uniform Flow
Occurs when the average depth of flow and velocity are
consistent within a reach. In this ideal case, the slope of the
water surface and the average slope of the channel are
equal.
Watercourse
The bed and shore of a river, stream, or other natural water
body; a canal, ditch, reservoir or other man-made surface
feature.
Watershed
The area that drains into a stream or river.
Water Management
Planning
A decision-making process for balancing the various
resource and other uses of a watershed.
Weir
A low dam built across a stream to raise the upstream
water level.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
APPENDIX C: SELECTED READINGS
This appendix presents selected readings that have been used as sources for the discussion
of hydroelectric practices in Section 3. Further references are provided in the following
research database that is available from CEA offices:
Canadian Electricity Association. 1999. Canadian Hydroelectric Utilities Environmental
Studies. Excel Spreadsheet. Ottawa, ON: CEA.
Reservoir Management
Bodaly, R.A., R.E. Hecky, and R.J.P. Fudge. 1984. “Increases in fish mercury levels in
lakes flooded by the Churchill River diversion, northern Manitoba,” Canadian
Journal of Fisheries and Aquatic Sciences 41: 682-691.
Bodaly, R.A., and Neil E. Strange, North/South Consultants Inc. 1997. "Mercury in fish in
northern Manitoba reservoirs and associated water bodies : summary report for
1992, 1994 and 1996 sampling". Sponsored by: Canada. Dept. of Fisheries and
Oceans, Manitoba Hydro, Manitoba Dept. of Natural Resources and HydroQuebec.
Hydro-Quebec, Environment Branch and University of Sherbrooke, Faculty of Applied
Sciences. 1991. "Influence of environmental factors on mercury release in
hydroelectric reservoirs" For the Canadian Electrical Association, Research and
Development; Principal investigators: Ken Morrison, Normand Therien.
Lycotte, M., R. Schetagne, N. Therieu, C. Langlois, and A. Tremblay. 1999. Mercury in
the Biogeochemical Cycle; Natural Environment and Hydroelectric Reservoirs of
Northern Quebec (Canada).
North/South Consultants Inc. 1999. Environmental Effects of Hydroelectric Generation in
Canada. Report Prepared to Provide Background for the Environmental Choices
Program. Winnipeg, MN: NSC.
Long-term Flow Management
Armour, C.L., and J.G. Taylor. 1991. “Evaluation of the Instream Flow Incremental
Methodology by U.S. Fish and Wildlife Service Field Users,” Fisheries, Vol. 16,
No. 5, pp. 36-43.
Caissie, D., and N. El-Jabi. 1995. “Comparison and regionalisation of hydrologically
based instream flow techniques in Atlantic Canada,” Canadian Journal of Civil
Engineering 22:235-246.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 65
Castleberry, D.T., J.J. Cech Jr., D.C. Erman, D. Hankin, M. Healey, G.M. Kondolf, M.
Mangel, M. Mohr, P.B. Moyle, J. Nielsen, T.P. Speed, and J.G. Williams. 1996.
“Uncertainty and Instream Flow Standards,” Fisheries, Vol. 21, No. 8, pp. 20-21.
Hubert, W.A., C. Raley, and S.H. Anderson. 1990. “Compliance with Instream Flow
Agreements in Colorado, Montana and Wyoming,” Fisheries, Vol. 15, No. 2, pp. 8-10.
Jacques Whitford Environment, Acres International Ltd., and T. R. Payne and Associates.
1996. Evaluation of Instream Flow Needs Assessment Methodologies in
Newfoundland. Report to the Canada - Newfoundland Agreement Reporting
Water Resource Management and the Green Plan, Habitat Action Plan.
Studley, T.K., J.E. Baldrige, and S.F. Railsback. 1996. “Predicting Fish Population
Response to Instream Flows,” Hydro Review, Vol XV, No. 6, pp. 48-56.
Conder, A.L., and T.C. Annear. 1987. “Test of weighted usable area estimates derived
from a PHABSIM model for instream flow studies on trout streams,” North
American Journal of Fisheries Management 7: 339-350.
Lamb, B.L. 1989. “Quantifying instream flows: matching policy and technology.” In L.J.
MacDonnell, T.A. Rice, and S.J. Shupe (eds.), Instream Flow Protection in the West.
Denver, CO: Natural Resources Law Centre, University of Colorado School of Law.
Lewis, A.F., A.C. Mitchell, and C.M. Prewitt. 1994. Evaluation of the effectiveness of water
release as a mitigation to protect fish habitat. Report prepared for the Canadian
Electrical Association by Triton Environmental Consultants Ltd. and E.A. Engineering
Science and Technology. CEA Report 9118 G 878. Montreal, Canada, TECL.
Mathur, D., W.H. Bason, E.J. Purdy, Jr., and C.A. Silver. 1985. “A critique of the Instream
Flow Incremental Methodology,” Canadian Journal of Fisheries and Aquatic
Sciences 43: 1093-1094.
Reiser, D.W., T.A. Wesche, and C. Estes. 1989. “Status of instream flow legislation and
practices in North America,” Fisheries (Bethesda) 14(2): 22-29.
Tennant, D.L. 1976. “Instream flow regimes for fish, wildlife, recreation, and related
environmental resources. In J.F. Osborn and C.H. Allman (eds.), Proceedings of
the Symposium and Specialty Conference on Instream Flow Needs. Volume 2.
American Fisheries Society, Bethesda, Maryland.
Short-term Flow Management
Cushman, R.M. 1985. “Review of ecological effects of rapidly varying flows downstream
of hydroelectric facilities,” North American Journal of Fisheries Management
5:330-339.
Higgins, P.S., and M.J. Bradford. 1996. “Effectiveness of large scale fish salvage to
reduce the impacts of controlled flow reduction in a regulated river,” Journal of
American Fisheries Society.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Higgins, P.S. 1995. Flow Ramping at Hydroelectric Discharge Facilities: Methodologies
for Impact Assessment and Mitigation. Report No. EA 94-07. Vancouver, BC:
Strategic Fisheries Safety and Environment, BC Hydro.
Hirst, S.M. 1991. “Impacts of the operation of existing hydroelectric development on
fishery resources in British Columbia,” Vol. I. Anadromous salmon. Can. Manuscr.
Rep. Fish. Aquatic. Sci. 2093.
Hunter, M.A. 1992. Hydropower flow fluctuations and salmonids; A Review of the
biological effects, mechanical causes, and options for mitigation. Washington
Department of Fisheries Technical Report 119:46.
Lister, D.B. 1990. An assessment of the fisheries enhancement potential of BC Hydro
operations at Shuswap River. Report Prepared for BC Hydro Environmental
Resources. Vancouver, BC.
Klohn-Crippen Integrated. 1993. Norns Creek Fan Habitat Enhancement. Report
Prepared for BC Hydro Hydroelectric Engineering Division. Report No. KCI-128.
Vancouver, BC: KCI.
Milhous, R.T. 1991. “Instream flow needs below peaking hydroelectric projects.” In D.D.
Darling (ed.), Proceedings of the International Conference on Hydropower –
Waterpower ’91. Vol. 1.
R.W. Beck and Associates. 1989. Skagit River salmon and steelhead fry stranding studies.
Report Prepared for Seattle City Light. Seattle, WA: RWBA.
Spillway Operations
North/South Consultants Inc. 1999. Environmental Effects of Hydroelectric Generation in
Canada. Report Prepared to Provide Background for the Environmental Choices
Program. Winnipeg, MN: NSC.
Raymond, H.L. 1988. “Effects of hydroelectric development and fisheries enhancement
on spring and summer chinook salmon and steelhead in the Columbia River
basin,” N. Amer. J. Fish. Mgmt. 8: 1-24.
Ruggles, C.P., and D.G Murray. 1983. “A review of fish response to spillways.” Canadian
Technical Report on Fisheries and Aquatic Sciences No.1171.
Stokesbury, K.D.E., and M.J. Dadswell. 1991. “Mortality of juvenile clupeids during
passage through a tidal, low-head turbine at Annapolis Royal, Nova Scotia, N.”
Amer. J. Fish. Mgmt. 11: 149-154.
Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
Page 67
Synchronous Condensing Operations
Independent Science Group, The. 1996. Return to the River: Restoration of Salmonid
Fishes in the Columbia River Ecosystem. Report on the Fish and Wildlife Program
of the Northwest Power Planning Council. Portland, OR: ISG.
Powell, C., and A. Prince. 1999. Total Gas Pressure and Fish Depth Distribution Study in
the Columbia River Below the Hugh Keenleyside Dam. Vancouver, BC: Strategic
Fisheries, BC Hydro.
Dams and Fish Movement:
Acres Consulting Services Ltd. 1984. Biological Mitigative Measures for Canadian Hydro
Facilities. Canadian Electrical Association, No. 156 G 315.237.
Bell, M.C. 1991. Fisheries Handbook of Engineering Requirements and Biological
Criteria. Portland, OR: U.S. Army Corps of Engineers, North Pacific Division.
Clay, C.H. 1995. Design of Fishways and Other Fish Facilities, 2nd ed. Boca Raton,
FA: CRC Press.
Cook, T., and E. Taft. 1997. Engineering Feasibility Study for Improving Fish Passage
Facilities at the White Rock Hydroelectric Plant of the Gaspereau River, Nova
Scotia. Report Prepared for Nova Scotia Power Inc.
Ruggles, C.P. and N.H. Collins (Montreal Engineering Co.). 1981. Fish mortality as a
function of the hydraulic properties of turbines. Canadian Electrical Association
Report No. G 144.
Ruggles, C.P, T.H. Palmetter, and K.D Stokesbury. 1990. A critical examination of turbine
passage fish mortality estimates. Report prepared for the Canadian Electrical
Association. Report #801 G 658.
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Considering Fish and Fish Habitat in Existing Hydroelectric Operations and Maintenance
APPENDIX D: INSTREAM FLOW ASSESSMENT
METHODOLOGIES
Various methods have been used to determine instream flow requirements for fish and fish
habitat and other water uses. These methods range from professional judgement to
computer models of varying complexity to progressive testing of alternative regimes. The
following is a description of some common methodologies for instream flow assessment.
Professional judgement is used in the field by biologists and other multidisciplinary
professionals to determine the downstream water level downstream relative to the
discharge through a dam. When a suitable water level is determined, usually based on
visual observation of habitat, the minimum instream flow is established. This method has
the advantage of simplicity, cost-effectiveness, and limited resource requirements, but
lacks precision and scientific credibility.
Used primarily in New England, the Aquatic Base Flow method uses historic flow data to
determine the median flow for the lowest flow month (typically August or September), and
applies that level to the remainder of the year (Reiser et al 1989).3 This approach assumes
that a specific flow rate per unit of watershed area will provide an adequate minimum
flow. It is simple to use, if historic data is available, but cannot account easily for sitespecific biological concerns; nor can the method adequately and defensibly adjust for
spawning or incubation.
The Tennant Method prescribes eight categories of stream flow as fixed percentages of the
average flow (AF) at a particular site in the stream (Tennant 1976). For example, “good
flow” would be 20% of average flow for the period October to March, and 40% of
average flow for April to September. In the absence of hydrologic records, instream flows
can still be recommended on the basis of a surrogate indicator, e.g., drainage area. This
approach has the advantage of low cost and few data requirements, but again lacks
precision and site specificity.
The Modified Tennant Method is based on the repetition of Tennant’s steps in developing
the percentages of mean annual flow (MAF). This requires observing key habitats and
studying the stream during flows that are known to approximate percentages of MAF. A
table of recommendations such as Tennant’s flow categories is produced specific to the
species and streams of interest.
Based on the hydraulics rather than the hydrology of a stream system, the Wetted
Perimeter Method assumes a direct relationship between wetted perimeter and available
fish habitat. “Wetted perimeter” refers to the narrowest wetted bottom of the stream crosssection that is estimated to minimally protect all habitat needs (Lamb 1989). For the
stream in question, this perimeter is plotted against incremental changes in discharge.
The inflection point where small decreases in flow result in greater decreases in wetted
perimeter is set as the minimum flow. This method requires some fieldwork (although less
than IFIM below) and gives more site-specific information. However, it is not directly
related to actual habitat created and is qualitative in the selection of cross-sections.
3 See Appendix C for the references.
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The Habitat Quality Index uses statistical analysis to correlate environmental features of a
stream with fish population size (Lamb 1989). Considerable data are required related to
late summer flow index, annual flow variation, maximum summer temperature, nitrates,
benthic invertebrate density, shelter, eroding banks, submerged aquatic vegetation, water
velocity, and stream width. This method appears to be dependent on region-specific
information, since the various factors mentioned above may be more or less important
across regions when determining flow requirements. Therefore, the approach appears to
be appropriate, but significant local data may be required to correlate the relationships.
The Instream Flow Incremental Methodology (IFIM) was developed by the US Fish &
Wildlife Service Instream Flow Group to estimate the effect of flow change on trout in
small coldwater streams (Conder and Annear 1987, Mathur et al. 1985). It involves a
combination of integrated planning concepts for water supply, analytical models of
physical and chemical parameters, alternatives analysis, and negotiations. IFIM’s most
common component is the Physical Habitat Simulation program (PHABSIM) which
provides criteria for negotiating instream flow.
PHABSIM evaluates fish preferences for stream habitat under varying flow conditions. This
approach makes two important assumptions: (1) the flow regime is the major determinant
controlling fish abundance; and (2) fish respond directly to available hydraulic conditions.
An important part of PHABSIM is the development of habitat suitability curves, most
accurate when they are derived for the specific site of interest. IFIM (PHABSIM) is perhaps
the best effort yet to represent the relationship between physical conditions and biological
preference, but the method still has some uncertain assumptions and is extremely costly to
use. Furthermore, it is not clear that the methodology is directly applicable to other
regions of US and Canada, even with appropriate habitat suitability curves.
Adaptive management is a process that can be undertaken in cases where, due to the
complexity of the resources in question, the implications of an operating decision are not
completely understood. The process requires a willingness to test alternative hypotheses
(operating alternatives) while carrying out evaluations of the response of fish stocks or
other resources, as appropriate. The results of the evaluation studies are compared to
predetermined estimates of outcome so that the implications of the alternatives can be
better understood and the resulting information used to improve operations. In
watersheds with complex interacting parameters, adaptive management may require that
studies be carried out for many years during the testing of several different operating
protocols. The high degree of effort and associated costs of this methodology suggest that
it is best suited to situations involving high resource values.
The most common approach used in Canada today for determining instream flow is to
take the best elements of several methodologies and to customise and combine them in
an appropriate regionally adapted method. Elements of Tennant, Wetted Perimeter, IFIM
(PHABSIM), and other methods are being evaluated in most regions of the country. The
key elements to be considered include regional hydrological and hydraulic conditions,
specific species and habitat needs, and existing practices, commitments, and requirements
in each region.
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