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Environmental Flow Guidelines
A Technical Background Paper
December 2004
Contents
Introduction .............................................................................................................................1
What are environmental flows? ..............................................................................................2
Why does the environment need specific flows? ...................................................................2
Current Environmental Flow Guidelines .................................................................................3
Low flows ...........................................................................................................................5
Flushing flows ....................................................................................................................6
Special purpose flows ........................................................................................................6
Maintenance of impoundment levels .................................................................................7
ACT national responsibilities and the statutory basis for environmental flows ..................7
Statutory basis for environmental flows in the ACT ...........................................................8
National Waters .................................................................................................................9
Inter-jurisdictional issues (NSW, Commonwealth, ACT) ...................................................9
Process to review the environmental flow guidelines ......................................................... 11
Issues with the 1999 Environmental Flow Guidelines ......................................................... 11
The calculation of environmental flows ........................................................................... 12
Do environmental flows achieve their objectives? .......................................................... 12
Timing of environmental flow releases ........................................................................... 13
Environmental flows in urban water bodies .................................................................... 13
Low Flows and spawning flows....................................................................................... 13
Demonstrated needs flows ............................................................................................. 14
Environmental flows in times of drought ......................................................................... 16
The impact of environmental flows on water restrictions and on supply ........................ 17
Flushing flows in the Cotter river after the bushfires....................................................... 17
Why is groundwater included in the Environmental Flow Guidelines? ........................... 18
Improved public awareness about environmental flows ................................................. 18
Can you put too much water into rivers? ........................................................................ 18
Additional Materials ................................................................................................................. 20
Invitation to Comment .............................................................................................................. 20
Glossary ................................................................................................................................... 21
Introduction
Environmental flows are the flows of water in our rivers and streams that are necessary to
keep them healthy. We rely on our waterways for a range of functions, including biodiversity
conservation and recreation as well as provision of water for irrigation and domestic supply.
Our streams need to be healthy to provide these functions.
Consideration of environmental flows in the ACT reflects a growing appreciation across
Governments and in the Australian community of the degradation of some rivers and
waterways. Many of our streams are no longer healthy as they contain insufficient water in
them.
The importance of environmental flows was highlighted in the early 1990’s when the intense
irrigation demand in the Darling River resulted in low flows and blue green algal blooms over
hundreds of kilometres. In places the river was unfit for stock watering and recreation as well
as for domestic water supply.
Environmental Flow Guidelines specifying the flows required to maintain aquatic ecosystems
in the ACT were finalised in 1999. Since then water allocation and licensing in the ACT has
been based on the Guidelines; ensuring sufficient water is allocated for the environmental
needs of aquatic ecosystems in the ACT.
The 1999 Guidelines indicated a need for review after five years. It was anticipated that after
a five-year period we would have a better understanding of how well the Guidelines were
meeting their objectives. This review has now commenced and, with input from specialists
and the community, will lead to revised Environment Flow Guidelines in 2005.
The aim of this paper is to provide background on the environmental flows in the ACT and
how the current Guidelines were set. Additionally the document provides an overview of
some of the issues to be considered in the review of the Guidelines, and seeks input on these
and other issues.
Although this stage of the review process provides an opportunity for input, the formal
consultation will occur in 2005 when the draft Guidelines are released for a two month
consultation period.
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What are environmental flows?
Environmental flows are those flows of water in our rivers and streams which are needed for
healthy rivers and streams. Dams have an obvious impact on downstream flows and
environmental flow releases are required below dams to reduce the impact of changed flows
on downstream aquatic ecosystems. In this situation environmental flow releases are usually
designed to mimic the natural flow regime as much as possible.
Environmental flows are also required in streams that are not dammed (unregulated streams)
as the flow in such streams can be affected by water abstractions or diversions. Here too the
environmental flow releases are usually designed to mimic the natural flow regime as much
as possible.
Environmental flows are defined in the 1999 Environmental Flow Guidelines as:
“…The stream flow necessary to sustain habitats (including channel morphology and
substrate), encourage spawning and the migration of fauna species to previously
unpopulated habitats, enable the processes upon which succession and biodiversity
depend, and maintain the desired nutrient structure within lakes, streams, wetlands
and riparian areas. Environmental flows may comprise elements from the full range
of flow conditions which describe long term average flows, variability of flows
including low flows and irregular flooding events.”
The best environmental flow is the natural flow that would exist if there were no diversions
from the river. However, our rivers and catchments fulfil multiple functions like domestic
water supply, recreation and biodiversity conservation, requiring a balance of environmental,
social and economic considerations in determining how much water should be released for
the environment.
The volume of water and the timing of flows specified in the 1999 Guidelines were determined
to protect the health and viability of both river systems, and associated ground water basins
and were based on best scientific knowledge at the time. Different flows were developed for
different types of water bodies and different climatic conditions.
Why does the environment need specific flows?
Stream ecosystems are adapted to particular flow regimes that determine both the physical
structure of the stream and the species that occur. Fish and other stream life are adapted to
particular flow regimes. They feed, breed, spawn and migrate in response to natural flow. If
we change the flow patterns it can affect habitat availability, food supplies, chemistry and
nutrient processing. This can lead to a loss of biodiversity, a decline in the ecological
condition and a decline in river water quality.
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As an example, modified flows allow sediment to accumulate on the streambed, changing
available habitat and nutrient processes which in turn affect the animals and fish living in the
stream. Modified flows also favour growth of algae including blue green algae, can also
facilitate the invasion and success of exotic pests like carp. The following table summarises
some of the effects of modifying natural flows in the ACT.
Table 1
Effects of modifying natural flows
Physical effect
Expected biological response
Reduction of channel width leading
Loss of some species
to loss of habitat
Reduced disturbance of streambed
Change in the community structure of fish and
macroinvertebrates in response to changes in
streambed and stream shape
Streambed stabilisation, formation
Increase in reed beds and decrease in normal
of islands, benches and bars and
algae
vegetation encroachment
Infill of the gravel beds in rivers with
Change in the community structure of fish and
sediment
macroinvertebrates in response to changes in
streambed and stream shape
Deposition of fine organic material
Change in the fungi and bacteria in streams,
affecting the entire food web
Low dissolved oxygen levels impacting on fish and
macroinvertebrates
Current Environmental Flow Guidelines
The current Environmental Flow Guidelines (EFG) were finalised in 1999 to;

establish water requirements in streams and lakes; and

to ensure aquatic ecosystems are protected.
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At that time the Guidelines were developed using the best available scientific knowledge from
local experts and apply to all rivers, streams, urban lakes and groundwater in the ACT except
Lake Burley Griffin.
The approach used in the EFG was to identify the types of aquatic ecosystems that occurred
in the ACT, and then set specific flow regimes to protect them. Four major types of
ecosystem were identified, and are set out in the table below together with the management
goals of the ecosystem as specified in the Territory Plan.
Type of aquatic
Description
Management goal
ecosystem
Water bodies in
this category
Natural
Ecosystems that
Primary goal:
Namadgi National
ecosystems
have persisted from
maintain ecosystems
Park not including
a period prior to
in their pristine state,
the Cotter
European settlement
Secondary goal:
catchment
recreation
Modified
Ecosystems modified
Should met a range
Rivers, lakes and
ecosystems
by catchment
of functions:
streams outside
activities (land use
recreation, and
Namadgi and the
change, discharges)
conservation
Canberra urban
or by changes to the
areas including
flow regime
Molonglo (except
Lake Burley Griffin)
Water supply
Ecosystems in
Primary goal: provide
Cotter River
ecosystems
catchments that
water supply,
catchment
provide the ACT
Secondary goal:
water supply
conservation
Created
Ecosystems in urban
Should meet a range
All urban lakes and
ecosystems
lakes, ponds and
of functions;
streams
streams that have
recreation,
developed since
conservation, and
urbanisation
irrigation
In the ACT an approach termed the ‘building block’ approach was used to determine the
environmental flows necessary to protect aquatic ecosystems. With this approach the
different flow ‘blocks’ deemed crucial for a river are identified and together build up the total
flow requirements.
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Four flow components were identified for ACT water bodies:

low flows;

flushing flows;

special purpose flows; and,

maintenance of impoundment levels.
Low flows
The protection of low flows was one of the primary goals of the Guidelines. Aquatic
ecosystems in the ACT have evolved to cope with the quite variable streamflows in the
region. For much of the time the flow in our streams is relatively low, with occasional larger
floods. In our smaller streams there are also periods when flow ceases under natural
conditions. These conditions are presumed to have occurred before European settlement
and still occur in pristine catchments. Natural low or no flow periods are important to aquatic
ecosystems. However, the stress from low flows should not be exacerbated by unnaturally
long periods of low or no flow. Aquatic ecosystems are particularly sensitive to impact from
other disturbances when stressed, and unnaturally long periods of low flow will result in
harmful impacts. In consequence the current Guidelines recognise that low flows need to be
maintained as close to natural levels as possible. The Guidelines identified the 80 th percentile
flow as the low flow level that needed to be protected.
What are flow percentiles? These are a way of describing flows in streams with variable
flows. The 80th percentile flow is that flow that occurs on 80 per cent of occasions and so are
low flows. Conversely the 5th percentile flow would only occur 1 day in 20 and would be a
large flow.
In both water supply and non-water supply sub-catchments the 80th percentile flow in rivers
and streams are protected. In non-water supply sub-catchments these low flow are protected
by restrictions on abstraction. In water supply sub-catchments low flows are maintained by
releases below reservoirs.
The Guidelines also impose limits on the volume of groundwater that can be extracted. In the
ACT there is a link between groundwater and surface water. With our shallow aquifers,
rainfall entering the aquifer travels through and discharges back to the surface relatively
quickly. The low flow in our smaller streams is largely comprised of groundwater discharge.
Groundwater abstraction is limited to 10 per cent of recharge to ensure that we do not impact
on low flow in streams.
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Flushing flows
In addition to maintaining low flows, the Guidelines recognised that our aquatic ecosystems
are also adapted to floods. Smaller floods are particularly important to prevent sediment build
up in rocky bottomed sections of river from damaging aquatic habitat. This need was very
apparent recently in the Cotter River after the bushfires when a lot of sediment was washed
into the river.
The guidelines identified that flood events with an annual recurrence interval between 1:1.5
years and 1:2.5 years should be protected to ensure that stream shape and structure, and the
dependent ecological processes are maintained. In other parts of Australia floods of this size
have been found to be critical in maintaining the stream shape.
What is an annual recurrence interval? Floods in Australian rivers occur irregularly.
Generally larger floods occur less frequently than smaller floods. The annual recurrence
interval (ARI) tells you how long you would have to wait for a flood of a certain size. So a
flood with an ARI of 1:1.5 years is a flood which occurs on average every one and a half
years. This flood would be smaller than a flood with an ARI of 1:2.5 years which would occur
on average every two and a half years.
The Guidelines termed these flows ‘flushing flows’. In non-water supply catchments, flushing
flows are protected by restricting abstraction to 10% of the volume above the 80 th percentile
flow. This allows flood flows to travel down streams. The guidelines did not specify a
flushing flow regime for water supply catchments.
Special purpose flows
The Guidelines recognised that some rivers or streams might need a special purpose flow to
meet particular ecological requirements. These could be to inundate a wetland, or to facilitate
spawning of native fish. The Guidelines identified only one special purpose flow; the
provision of a spawning flow for Macquarie perch in the Cotter River between Corin Dam and
Bendora Dam. Macquarie Perch spawn in spring, and their spawning behaviour is triggered
by medium to high flows during this season.
The flow adequate for spawning was defined as the 50th percentile monthly flow during the
spring months and the 80th percentile flows during August, and December through March.
The spawning flow was required only two years out of every five. This timing was based on
the need to provide spawning opportunities at regular intervals, and the recognition that
spawning flows involved the release of a large volume of water from Corin Reservoir.
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Maintenance of impoundment levels
Aquatic plants (macrophytes) are an important component of aquatic habitat, and their
destruction affects dependent biota and associated ecosystem processes. In the current
Guidelines it was argued that stability of water levels in lakes and ponds affects the viability of
macrophytes. Should the water level of urban lakes and ponds be lowered too far for a
significant period, macrophytes might have been damaged or killed, compromising the
ecological values of those water bodies and their capacity to support other environmental
functions.
To protect lake and pond ecological values, a maximum draw down limit of 0.2 m was set.
This meant that for our urban lakes and ponds no abstraction was permitted if the water level
fell more than 0.2 m below the spillway.
ACT national responsibilities and the statutory basis for environmental flows
Water resources management including environmental flows in the ACT is guided by

national policies agreed to by the Council of Australian Governments (COAG)
to which the ACT is a partner; and

federal and ACT policies, agreements and legislation.
Council of Australian Governments (COAG)
The ACT is a signatory to the 1994 COAG strategic framework for the efficient and
sustainable reform of the Australian water industry. Amongst other things, this agreement
commits parties to the implementation of environmental flows based on the best available
scientific advice. As part of the national competition policy reform package agreed to by the
Commonwealth and all states and territories in 1995, jurisdictions agreed that Competition
Payments by the Commonwealth to the States and Territories would be dependent on
successful implementation of these reforms. Through the enactment and implementation of
the Water Resources Act 1998 in particular, including the provision of environmental flows,
the ACT complies with these agreements.
These COAG reforms have assisted the national recognition that the provision of appropriate
environmental flows is a necessary condition in maintaining the functioning of healthy
ecosystems and ensuring that aquatic ecosystems can continue to provide a broad range of
valued services such as those relating to water supply; assimilation, treatment and disposal of
wastes; aesthetics; and recreational, educational, and conservation opportunities.
Accordingly, all jurisdictions now have statutory requirements for the provision of
environmental flows. A range of research is continuing which will improve the scientific
advice available in setting appropriate flows.
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Murray Darling Basin Initiative
The ACT participates in the Murray Darling Basin Initiative through involvement in the Murray
Darling Basin Ministerial Council and the Murray Darling Basin Commission. This is in
recognition that actions in upstream parts of the Basin such as the ACT can have impacts
downstream and that a cooperative approach will ensure the most effective management of
the Basin’s resources.
Other jurisdictions in the Initiative have set a limit on diversions (known as the “Cap”) and the
ACT participation includes a commitment to set a Cap on ACT diversions. The ACT is
currently considering what an appropriate Cap might be. It is important to note the
relationship between the setting of environmental flows and the Cap. Environmental flows are
the flows necessary to maintain the health of aquatic ecosystems. Once set the total amount
of water available for use from individual river valleys and the Murray Darling Basin as a
whole can be determined. The Cap refers to how the total amount of water available for use
in the Murray Darling Basin is shared amongst jurisdictions.
In terms of total Basin water use, the quantity of water used by the ACT is minimal.
Potentially more significant is the need to continue to ensure that water quality impacts are
minimised along with alterations in flow patterns. However, the existence of Burrinjuck Dam
restricts the impacts from the alteration in flow patterns.
Statutory basis for environmental flows in the ACT
In the ACT water resource management is principally guided by the Water Resources ACT
1998, though there are also responsibilities under the Environmental Protection ACT 1997,
and Land (Planning and Environment) ACT 1991. Provision of drinking water to the ACT
through the pipe network is dealt with under separate legislation and will not be discussed
here.
Water Resources Act 1998
The Water Resources Act 1998 provides for management and use of the Territory’s water
resources in a way that sustains the physical, economic and social well being of the people of
the Territory while protecting the ecosystems that depend on those resources.
The Environmental Flow Guidelines is a statutory instrument under the Water Resources Act,
setting out the environmental flow requirements for all waterbodies in the ACT, including
groundwater. The Water Resources Management Plan is a further statutory instrument under
the Water Resources Act 1998 that describes Territory water resources, proposed allocations,
water allocations for various uses, and action to be taken to manage water resources.
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Environment Protection Act 1997
The Environment Protection Act 1997 provides protection for the environment from pollution
and other forms of environmental harm, and includes integration of environmental, economic
and social considerations in decision-making processes. It sets water quality standards which,
together with the flows set by the Guidelines, are the two key elements that determine
ecosystem health.
Land (Planning and Environment) Act 1991
The Land (Planning and Environment) Act 1991 provides for preparation of the Territory Plan
that identifies water use and catchment policies. The water use and catchment policies of the
Territory Plan recognise the competing and often conflicting demands made on the Territory’s
water resources. They protect the waters and catchments of the ACT by specifying permitted
uses and environmental values for each water body. There are three types of water use
catchments according to the predominant water use or environmental value within that
catchment. These are:

conservation of aquatic habitat

provision of domestic water supply

provision of drainage and open space.
Secondary uses are also permitted for individual waterways, as long as they do not
compromise maintenance of the standards required to meet primary environmental value.
The Environmental Flow Guidelines recognise these primary and secondary values for
catchments in setting flow requirements in different catchments.
National Waters
Lake Burley Griffin, although it is within the ACT, remains the responsibility of the
Commonwealth and is not subject to the Water Resources Act 1998 or the Environmental
Flow Guidelines. The lake is managed by the National Capital Authority (NCA), guided by the
Lake Burley Griffin Management Plan. Nevertheless, both ACT and Commonwealth agencies
have recognised the need to ensure consistency across the ACT, given the impracticality of
considering the management of Lake Burley Griffin in isolation. In consequence, through
agreement with the NCA, the current Environmental Flow Guidelines include reference to
Lake Burley Griffin which and are also explicitly recognised in the Lake Burley Griffin
Management Plan.
Inter-jurisdictional issues (NSW, Commonwealth, ACT)
Under the Commonwealth Seat of Government Acceptance Act 1909, an agreement between
the Commonwealth and New South Wales governing the area which became the Australian
Capital Territory was ratified. Amongst other things, this agreement which is a schedule to
both the this Act and the NSW Seat of Government Surrender Act 1909, provides the
Commonwealth with paramount rights to the use and control of waters of the Queanbeyan
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and Molonglo Rivers and their tributaries which lie in NSW, for all the purposes of the
Territory. The rights of NSW and its residents to the waters of these rivers are subject to and
secondary to this paramount right.
Through this agreement, NSW also has continuing obligations to not pollute and to protect
from pollution the rivers throughout their whole course above the Territory and, except with
Commonwealth agreement, to preserve from sale, occupation and lease Crown lands within
the catchment areas of the Queanbeyan and Molonglo Rivers.
The water resources of the Molonglo and Queanbeyan Rivers have long been utilised for a
range of purposes in the ACT including in particular:

supporting the aesthetic, recreational, ecological and National Capital purposes of Lake
Burley Griffin and the Molonglo River in the ACT;

supporting the long established irrigation and other water use enterprises in the
Territory particularly those in the Pialligo/Fyshwick area and surrounding Lake Burley
Griffin;

supporting the Jerrabomberra wetlands which are wetlands of national importance;

providing urban water supply to the Territory (including the currently developed areas in
Queanbeyan).
Through the Canberra Water Supply (Googong Dam) Act 1974), the Commonwealth
developed the water resources of the Queanbeyan River specifically for ACT urban water
supply purposes through the construction of the Googong Dam. By amendments to this Act
at the time of self-government, the Territory Executive controls the waters (and land) of the
Googong Dam Area (5000 hectares of land comprising the dam and its foreshores).
The ACT’s Water Resources Act 1998 was developed to cover all waters under the control of
the Territory Executive including those of the Googong Dam Area. Accordingly, the
Guidelines specify the environmental flows that are to be released from the Googong Dam.
While the Commonwealth has paramount rights to the waters of the Molonglo and
Queanbeyan Rivers, and the waters of these rivers are important for supporting a range of
purposes in the ACT, the ACT has no specific jurisdiction or management control over these
waters in NSW (except within the Googong Dam Area). Currently the Commonwealth also
does not identify what water use practices and flows it sees as consistent with its paramount
rights. Nevertheless, the Guidelines are intended to identify the flows that the ACT sees as
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consistent with protecting the Commonwealth’s paramount rights and necessary to support
ACT water use dependent on the resources of the Queanbeyan and Molonglo Rivers
(including Jerrabomberra Creek in NSW). The ACT is pursuing the appropriate management
of these waters in NSW in the context of formalising urban water supply to Queanbeyan.
Process to review the environmental flow guidelines
The process to review of the Guidelines is described below. The guidelines are being
updated based on the latest scientific understanding and information, and input from
stakeholders and the community.
The initial component is a scientific overview of flow requirements. The Cooperative
Research Centre for Freshwater Ecology (CRCFE) was engaged to draft a report on the
performance of the Guidelines and to suggest improvements. Specialists in that organisation
drew upon the increased understanding of environmental flows since 1999, and local
research conducted on some of our rivers. This stage has been completed. A copy of the
CRCFE report ‘Review of the 1999 ACT Environmental Flow Guidelines’ is available on the
Environment ACT website, or from the Environment ACT helpdesk.
The second stage of the review is an identification and discussion of further issues that need
to be considered in the review. This component commenced with a forum of key
stakeholders who flagged key issues associated with environmental flows. These issues, and
others identified during the administration of the ACT water resources, are included in this
background paper. Input is sought at this point on these or other issues to do with
environmental flows.
Input received from the community and stakeholders, and the scientific input from the
CRCFE, will be used to revise the Guidelines. These draft Guidelines will then be made
available for public comment for a two month period. It is expected that this consultation
phase will occur towards the middle of 2005.
The Guidelines are a disallowable instrument under the Water Resources Act 1998. At the
completion of the consultation process finalising the Guidelines would require tabling in the
Legislative Assembly.
Issues with the 1999 Environmental Flow Guidelines
Following are a set of issues that have been raised by stakeholders or experienced in
administration of the 1999 Environmental Flow Guidelines. Accompanying each issue is a
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brief discussion. The listing below is not intended to be complete, your views on any of these
issues or others you may wish to raise would be valued.
The calculation of environmental flows
The calculation of volumes of water for environmental flows is based on mean monthly
discharge. Rivers in the ACT have highly variable discharge over a year. Flows are naturally
higher in winter, but even within seasons, discharge can be highly variable. Environmental
flows are currently calculated based on average monthly flows because flows over a year do
not account for this variability, and flows calculated on a shorter time interval would be difficult
to administer. The mean monthly flows are calculated from the monthly flow records from the
time when gauging records were first recorded to the current year.
Within the water supply catchments the flow releases are structured to reflect natural flow
conditions. If natural inflows to a reservoir drop then the releases also drop, mimicking
inflows. With this calculation approach environmental flows would reflect increased water
yields in the ACT as a result of regrowth of fire-affected forest. Similarly, if climate change
reduced runoff less water would be released for environmental flows. Another factor that may
need to be considered is whether human changes to the climate, like cloud seeding in nearby
areas in NSW, will have an effect on runoff in the ACT and how such effects should be
considered in environmental flow guidelines.
Do environmental flows achieve their objectives?
Environmental flow regimes have been developed for the four ecosystems identified in the
Territory Plan. Low and flushing flows are protected in these ecosystems. While each of
these ecosystems has different land use impacts, and stressors on the biodiversity and
ecology of the waterways, the protection of flows should allow critical habitat to be maintained
for fish, macroinvertebrates, macrophytes, birds, and other aquatic biota.
To determine if targets and thresholds for environmental flows are appropriate, the need for
monitoring programs was flagged in the Guidelines. There has been considerable
assessment of environmental flows in the Cotter River, which has provided good information
on the effectiveness of the environmental flow regime. Outside of water supply catchments
environmental indicators have been monitored by Environment ACT; focussing particularly on
water quality, fish and macroinvertebrates. The CRCFE review identified that this latter
monitoring was not able to identify whether the environmental flows in the non water supply
catchments were meeting their objectives or not. Part of the reason for this was that such
catchments are subject to a mixture of impacts, including flow changes, making it difficult to
isolate the effects of environmental flows. A suggestion made in the CRCFE report is that
more focussed monitoring be undertaken to determine if environmental flows are achieving
their objectives.
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Additionally, the CRCFE review document suggested that the Guidelines should contain
clear operational objectives that were linked to appropriate monitoring and assessment
programs. Such a process would assess future assessment of the performance of the
environmental flow guidelines.
Timing of environmental flow releases
Both the timing and the volume of water in environmental flows can be important. For
example, the spawning flow release has to be made at the right time of year for it to be useful.
The recent research on the Cotter has shown the importance of the timing of flows to the
stream health. As another example, a high volume release during an otherwise dry period
could have a detrimental affect on native fish or other aquatic biota that have lifecycles
adapted to dry periods. In the Cotter River prior to the drought, flow releases below Bendora
Reservoir each month consisted of the low flow component for three weeks followed by
higher flows in the fourth week.
With our improved knowledge of flow-biota relationships there is an opportunity in the revised
Guidelines to be more precise about the timing as well as the volume of flows.
Environmental flows in urban water bodies
Despite the considerable modifications urbanisation has caused, urban streams have high
recreation and aesthetic values. In particular, high value is placed on the constant flow in
urban streams resulting from increased catchment runoff from all the roads and roofs. In
these catchments streams can be stressed because there is too much water and it comes off
the catchment too fast. Stressed systems respond poorly to extreme events like drought. In
urban ecosystems, like elsewhere, the flows above the 80th percentile are protected against
abstraction. However, to protect urban streams from the impacts of the additional urban
runoff, the additional volume from roofs and roads is not part of the low flow and is available
for abstraction. This approach serves two functions; it protects streams from unnaturally high
flows and it allows use of second class water in the urban area.
Low Flows and spawning flows
Low flows are protected by restrictions on abstraction of flows above the 80 th percentile. The
80th percentile flows were chosen, using the best available science at the time, as the volume
most likely to protect the ecology of streams from unnatural low flows. The monitoring of
environmental flow releases has indicated that this level is adequate for protecting
environmental values. For the revised Guidelines we need to resolve whether the current
protection of low flows is adequate or should be modified.
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In relation to spawning flows, the Cotter River is home to two endangered fish species, the
Two Spined Blackfish, and the Macquarie Perch. These fish are not found in significant
numbers elsewhere in the ACT or nearby NSW. In order to protect and maintain these
populations, the Guidelines made provision for special spawning flows to be released at
specific times of the year in order to provide the right conditions for Macquarie Perch to
successfully breed. These requirements were based on the best available knowledge of the
breeding needs for Macquarie Perch. Spawning flow requirements were met in 2000 but
there have been no spawning flow releases recently as a result of the drought, 2003 fires, and
the situation of our water supply.
Nevertheless data collected since the implementation of the guidelines suggests that the fish
have successfully bred without special spawning flows. The need for spawning flows in the
revised Guidelines needs to be carefully considered.
Demonstrated needs flows
For the water supply catchments the Guidelines contain a provision allowing for a reduction in
the environmental releases required if the water supply provider can demonstrate a need for
this action. The Guidelines are not specific as to the circumstances in which this is
applicable, but limit the reduction in flows to 50 per cent. During the initial phase of the
current drought the environmental flows were reduced by 50 per cent as it was considered
that a need had been demonstrated to make more water available to meet domestic needs.
The uncertainty in the current Guidelines about ‘demonstrated needs’ makes it more difficult
to manage for a domestic water supply in times of drought as the supplier is unclear if and
when these provisions would come into force. Several suggestions for clarifying this
arrangement in the revised Guidelines have been made. As the demonstrated needs
provision currently acts as a type of drought response, the provision could be removed
entirely and clearer arrangements made for environmental releases under drought.
Alternatively the “demonstrated needs” provision could be retained for circumstances other
than drought, for example infrastructure failure, or the provisions could be more tightly linked
to water restrictions.
What about effects of abstractions and environmental flows in neighbouring NSW?
The ACT is an island within NSW. More specifically, it is wholly contained within the upper
Murrumbidgee catchment which in turn is part of the Murray Darling Basin. The
Murrumbidgee River rises in NSW, flows through the ACT and then returns to NSW. Other
streams particularly the Molonglo River, Queanbeyan River and Jerrabomberra Creek rise in
NSW before entering the ACT where they join the Murrumbidgee River. In addition, a part of
the Queanbeyan River in NSW, contained by the Googong Dam Area, is controlled by the
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ACT. Some important ACT streams such as the Cotter, Naas and Gudgenby rivers are
almost totally contained within the ACT.
Such geographic fundamentals highlight the value of cooperation with our neighbours and
that we must take account of what occurs in NSW. NSW like the ACT is party to the COAG
water reforms and is a party to the Murray Darling Basin Initiative and therefore has formal
obligations to ensure appropriate environmental flows in its streams. In addition, the
Commonwealth has paramount rights to the water of the Queanbeyan and Molonglo rivers in
NSW (including Jerrabomberra Creek) for all the purposes of the ACT.
The headwaters of the Murrumbidgee River in NSW have been dammed as part of the Snowy
Mountains Scheme (Tantangara Dam near Adaminaby). Up until recently, this dam diverted
almost all the water captured to Eucumbene Dam from where it was returned to the
Murrumbidgee River via the Tumut River. This combined with irrigation, town water supply
and other usage resulted in generally low flow in the Murrumbidgee River entering the ACT.
As apart of the decision to return water to the Snowy River, NSW has committed to a program
to return environmental flows to the Murrumbidgee upstream of the ACT.
In recognition that the resources of the Murrumbidgee upstream of the ACT have already
been fully utilised, and the fact that the ACT cannot lay any specific claim to the resources of
the Murrumbidgee River from NSW, the current guidelines commit the ACT to returning to
NSW that water which enters the ACT via the Murrumbidgee (in addition to any appropriate
ACT sub-catchment flows).
As noted earlier (under Jurisdictional Issues) the ACT relies on the water of the Queanbeyan
and Molonglo Rivers for a range of purposes, consistent with the Commonwealth’s paramount
rights to these water resources. While there is little large scale irrigation, NSW residents
living in these catchments also utilise the water resources. In particular, increasing rural
residential development brings with it an increasing number of farm dams and bores. Such
water use is generally not metered and is only loosely controlled. In addition, the large
number of dams add significantly to evaporative loss. The ACT has become increasingly
concerned at the potential of these developments increase water use in these catchments
and hence to reduce flow into Googong Dam and into the ACT. There are also concerns on
the likely impact they may have on water quality.
While catchment management and water use, including consistency with the
Commonwealth’s paramount rights to the waters of these rivers, are being pursued in the
context of water supply arrangements to Queanbeyan, the revised Guidelines could indicate
what environmental flows the ACT sees as appropriate for the waters over which the
Commonwealth has paramount rights. These flows would apply where the rivers enter the
ACT or the Googong Dam Area.
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While under the Seat of Government Acceptance 1909 the Commonwealth has paramount
rights to the waters of the Queanbeyan and Molonglo Rivers upstream of the ACT, under that
same legislation the ACT has an obligation to return waters to NSW (via the Murrumbidgee
River) in a fit state for irrigation and conservation. As by far the largest city in the Murray
Darling Basin the ACT has a good record in protecting water quality in downstream waters
through its urban water management and high standard of sewage treatment. This needs to
continue. The ACT also needs to minimise as far as possible impacts to downstream flow
patterns.
These matters highlight the interdependence of the ACT and NSW parts of the region and the
need for cooperation in management of the region’s water resources in order to maximise
sustainability outcomes, including benefits obtained from water resources.
Environmental flows in times of drought
In times of drought the environmental releases below water supply reservoirs are reduced.
Drought is defined in the Guidelines as occurring when in nine of the preceding 12 months
flows into Corin Dam and Googong Dam have been less than the median monthly inflows,
and the total amount of water in ACT water supply storages was less than 50 per cent of
capacity. The Guidelines do not specify what the environmental flow releases should be in
times of drought.
The ACT has experienced drought conditions as defined in the Guidelines since 2003.
Rather than specify a particular flow regime, the Environment Protection Authority specified
an adaptive management regime based on ongoing monitoring and research. Flow volumes
and timing of release below each reservoir was specified and the status of the aquatic
ecosystem monitored. The CRCFE review includes details of this program.
The pressures on a water supply are greatest during times of drought. Maintenance of a
domestic water supply is a vital outcome, but conversely drought conditions are when our
aquatic ecosystems are most stressed. Although occasional very low flows are natural for
Australian rivers, in water supply catchments these conditions are unnaturally prolonged,
particularly in times of drought. A delicate balance is required to ensure both the water supply
and the aquatic ecosystem values are maintained in these times. One suggestion made is
that the definition of drought needs to be simplified as water supply functions may be
threatened before we enter a ‘drought’. An approach here may be to link drought responses
to the water restriction scheme. Where the water supply provider identifies a need to impose
restrictions to protect the water supply, the environmental releases should also be reduced in
parallel.
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The impact of environmental flows on water restrictions and on supply
During the current drought and accompanying water restrictions it has been suggested that
the release of environmental flows below our water supply dams has been the principal cause
of our current state of restrictions. A further view is that our water supply system was
designed in a time when environmental flows were not considered and the need to meet
environmental flow releases now significantly compromises the ability of the system to meet
domestic demands.
In relation to water restrictions, advice provided by ActewAGL is that environmental flow
releases are not the single or even the major reason for our current level of restrictions. The
drought we are experiencing is the worst on record; worse even than the ‘worst’ drought used
to plan for the water supply reservoirs. To face this drought, water restrictions would have
been required whether we had been releasing environmental flows or not.
The point raised about the impact of environmental flows on long term provision of a water
supply is being investigated by ACTEW Corporation. ACTEW have been asked by
Government to consider whether the ACT needs to augment its water supply, and in this
investigation ACTEW are factoring in the need to provide for environmental flows. The
ACTEW report is to be delivered to Government in December 2004. Although it is recognised
that environmental flows were not considered in design of the water supply network, by and
large most parties now acknowledge the need to move on from this perspective. Providing
flows to protect aquatic resources should be a central part of the way we manage water
resources; and this obligation should be met in a conscientious fashion.
Flushing flows in the Cotter river after the bushfires
After the 2003 bushfires in the Cotter catchment, a large quantity of sediment and ash made
its way into the river. Fine sediment settles on the streambed and in streams below dams
there is often not enough flow to move the off downstream. Under natural flow regimes, this
sediment is moved downstream during periods of high flows. Sediment can smother the
habitat used by fish and other stream biota. During droughts streams are naturally stressed
and so after the bushfires there was an added imperative to remove the sediment load if
possible. Weighed up against this was the need to protect our water supply during this dry
time.
A series of carefully targeted flushing flows were instigated over the year following the
bushfires. These flows were sized to ensure they were large enough and frequent enough to
clean the river, but did not require excessive amounts of water. The CRCFE review reported
that this adaptive approach was successful in cleaning the river and maintaining the aquatic
ecosystem. Further work is planned to clean out the unnaturally large sediment deposits in
some of the pools. It would seem useful to incorporate some of these lessons learnt about
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how to effectively and economically meet environmental flow needs should be incorporated in
the revised Guidelines.
Why is groundwater included in the Environmental Flow Guidelines?
The Guidelines limit the amount of groundwater that can be extracted in a sub-catchment
because in the ACT there is a link between groundwater and surface water. For the most part
groundwater in the ACT is in shallow aquifers in the joints of the bedrock (a fractured rock
aquifer). These aquifers tend to be shallow (generally less than 100 m deep), and the water
from them is varies in quality from good to saline, and also in yield.
With this sort of shallow aquifer, rainfall percolates through the soil into the aquifer, travels
through the aquifer and discharges back to the surface, usually into streams at the bottom of
valleys. The low flow in our smaller streams is largely made up of this discharge except
during rainfall events. Any reduction in discharge from the aquifer would result in a reduction
in the low flows in the stream. Consequently, if there is over abstraction from groundwater in
a sub-catchment, streams that used to flow may dry up causing a significant impact on the
health of the stream.
In the Guidelines groundwater abstraction is limited to 10 per cent of recharge to ensure that
there is no significant impact on streams during periods of low flow.
Improved public awareness about environmental flows
The Environmental Flow Guidelines were written to meet a statutory requirement and
contained precise descriptions of flow components. This made the Guidelines difficult to
understand for a layperson. There is an increasing community awareness of environmental
flows and of their implications for water resource management. There is a need to provide
clearer information on what environmental flows are, their basis and their importance in water
resource management. The need for better community awareness has become apparent
with the airing of misconceptions such as “dams are required to ensure for environmental
flows”, and “environmental flows are very regular releases of water which damage
ecosystems”. A challenge for the revised Guidelines will be to communicate this information
more clearly.
Can you put too much water into rivers?
When discussing environmental flows normally we are talking about restoring or maintaining
flows in rivers. However, there are several circumstances in which we might have too much
flow in our rivers and this too can be a problem. The urban environment is the main area
where human changes have produced flows higher than are natural. This increase in flow is
not necessarily a good thing as the stream ecosystems are not adapted to these higher flows.
Most of the streams running through Canberra now flow all year round. Prior to development
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of the city these streams would have flowed only intermittently after rain. The impacts of
these changes on stream biota have been discussed in the section on urban flows.
Another area where flows are augmented is below our sewage treatment plants where treated
effluent is discharged. These discharges can significantly change the natural flow volume
and flow variability downstream. Discharges tend to be regular and consequently they both
unnaturally increase low flows in rivers and smooth out natural variation. This issue needs to
be considered very carefully as there are significant operational constraints on the way that
treatment plants can discharge treated effluent. Recent initiatives by ActewAGL to reuse
treated effluent will reduce the volume of effluent discharged and the downstream flow
effects.
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Additional Materials
Copies of the 1999 Environmental Flow Guidelines, and the CRCFE Review of 1999 ACT
Environmental Flow Guidelines are available in electronic format from the Environment ACT
website.

The 1999 Environmental Flow Guidelines can be downloaded from
http://www.environment.act.gov.au/Files/environmentalflowguidelines.pdf
Alternatively hard copies are available from the Environment ACT helpdesk in
Macarthur House, 12 Wattle St, Lyneham ACT

The CRCFE report:
Ogden , R., Davies, P., et al, (2004)The Review of 1999 ACT Environmental Flow
Guidelines: A report by the Cooperative Research Centre for Freshwater Ecology to
Environmental ACT November 2004 can be downloaded from the Environment ACT
website.
Invitation to Comment
This is an important opportunity to contribute to setting the future Environmental Flow
Guidelines for the ACT. We welcome your ideas on the issues raised in this document, and
value your contribution of further issues.
Your comments should be sent by close of business 11 February 2005 to:
Environmental Flow Guidelines
Water Resources Unit
Environment ACT
PO Box 144
LYNEHAM ACT 2602
Comments can also be emailed to [email protected]
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Glossary
Abstracter
An abstracter is a person or corporation that abstracts water from a
waterway, dam or bore.
Abstraction
Abstraction refers to the removal of water from a natural waterway, dam
or bore.
Aquatic ecosystem
For the purposes of the Environmental Flow Guidelines, an aquatic
ecosystem is an ecosystem bounded by the riparian zone.
Aquifer
An aquifer is a layer of rock or soil that is permeable and has the capacity
to convey significant amounts of groundwater.
Baseflow
Baseflow describes the quantity of flow in a waterway that exists purely
as a result of seepage into the upstream channel from groundwater.
Practically, baseflow is determined from either field investigation after a
prolonged period without precipitation or one of several quantitative
baseflow separation models.
Biota
Biota is a general term describing the animal or plant life of an area.
Created ecosystem
A created ecosystem is an ecosystem, usually in an urban area, that has
been significantly altered to another which is now valued for its new
characteristics.
Discharge
Discharge refers to the release of water from a detention structure into a
waterway.
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Diversion
See abstraction.
Drawdown
Drawdown refers to the change in water surface elevation in a dam
during a certain time period.
Ecosystem
An ecosystem is a biological community of interacting organisms and
their physical environment.
Flow regime
Flow regime commonly describes the flow over time for a particular
waterway. It is similar to a unit hydrograph.
Flushing flows
Flushing flows are small flood flows designed as part of the
environmental flow program to achieve particular channel maintenance or
other outcomes.
Fractured rock aquifer
A fractured rock aquifer is an aquifer that exists where the geological
structure is characteristically impervious rock with sediment filled
fractures. These fractures allow the conveyance of groundwater.
Macroinvertebrates
Macroinvertebrates are the small insects, worms, and crustaceans that
are found in water bodies.
Macrophytes
Macrophytes are large water plants. Emergent macrophytes are plants
that are rooted in the riverbeds or lakebeds, and protrude from the water
surface. Submerged macrophytes are plants that are rooted in the
riverbeds or lakebeds, but do not protrude from the water surface.
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Modified ecosystem
In the context of this document a modified ecosystem is an ecosystem
that has been somewhat altered by direct or indirect human influence.
Natural ecosystem
A natural ecosystem is an ecosystem on which there is minimal human
impact.
Percentile
A percentile is a value between 0 and 100 that indicates the proportion of
measurements that fall above the percentile value. In this document the
range of stream flows are expressed in percentiles. The 80th percentile is
that flow that is exceeded 80% of the time; these are low levels of flow.
The 50th percentile, or median is that flow that is exceeded only half of the
time, and so would be a higher flow.
Percentage
Where a percentage is used in conjunction with a percentile such as 10
per cent of the flow above the 80th percentile, this refers to the portion of
the water available for abstraction (10 per cent) when certain flow
conditions prevail (the flow exceeds the 80th percentile). It refers only to a
portion of the water above the threshold level, not a portion of all water
flowing at the time.
Riparian vegetation
Riparian vegetation is terrestrial vegetation that is influenced by its
proximity to a body of water.
Special purpose flows
A special purpose flow refers to a particular flow regime that is required to
meet a specified purpose. For example, some fish require a relatively
unique flow regime, in terms of flow and temperature, to occur before
spawning is initiated.
Stressed stream
A stressed stream is a stream that has endured a prolonged period of low
flow. These conditions are often detrimental to stream health yet are a
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necessary component of the flow regime because they improve the
resistance of local organisms to periods of low flow or drought conditions.
A stressed stream may also refer to a stream that is suffering from
pollution.
Territory Plan
The Territory Plan is the primary planning document that implements the
Land (Planning and Environment) Act 1991 and provides a framework for
the sustainable growth of the ACT region. It provides specific guidelines
and restrictions on land use.
Urban lake or pond
An urban lake or pond is a dam that was constructed for the purposes of
recreation, pollution control and minimisation of peak storm flows. In the
ACT they are Point Hut Pond, Isabella Pond, Upper Stranger Pond,
Lower Stranger Pond, Lake Tuggeranong, Lake Ginninderra, Gungahlin
Pond, Yerrabi Pond.
Water supply ecosystem
A water supply ecosystem is an ecosystem in a catchment, which is
primarily used as a water supply catchment.
Water use restrictions
Water use restrictions are rules that are put in place during periods of
drought or near-drought to prevent the excessive drawdown of water
supply reservoirs. Examples of water use restrictions include limited
sprinkler hours and prohibition of outdoor watering.
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