Download WaterWorks Watershed Activity

WaterWorks Watershed Activity 1
What is a watershed?
Ask visitors if they have ever heard of the term “watershed.” Provide a
simple definition for a watershed – the land area that drains into a river,
lake, or other body of water. The Earth is made up of numerous
watersheds, some containing more of the Earth’s (fresh) water than
others. Do the following activity to demonstrate what a watershed is. It can be
done individually or in groups. Ask each group or individual to:
Materials:
- Piece of white paper
- blue, black, brown, and red
water-based marker
- assorted (colors) water-based
markers
- Water sprayer filled with water
Instructi ons:
Crumple a piece of paper into a loose ball.
Partially open the paper, and place it on a desk. The paper should still be
crumpled enough to have portions that resemble mountain ridges and
valleys.
Using a blue water-based marker, have visitors mark streams or rivers on
their papers, and also have them mark where they think the water will
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collect as it runs downhill. (This could represent a lake).
Using a black water-based marker, have visitors outline the ridges that
separate one stream or river from another.
Using brown water-based markers, have visitors draw exposed soil that
could erode or wash away into the lake as the water flows through the
watershed.
Using different colors of markers have visitors draw in where they could
place a city, farm and industrial area on their land. Have them think about
where they are putting them and have them think about their water
sources and their effect on the water sources.
Using red water-based markers, have students draw in some pollutants
that may be found in their watershed, such as industrial waste, pesticides
from lawns, and animal waste from a nearby farm. Keeping the model on
the desks, have visitors spray (or you go around with a sprayer and
spray) a very light mist of water over it.
Observe where water runs down and collects. Questions to conside r and ask during workshop:
o What do you think the paper represents?
o What do you think the spray represents?
o Why does water flow down into the creases?
o What would you call the water that runs down in the creases?
o And the water that collects in “pools”?
o What happened to the ink from the markers as the water flowed?
Where did it end up?
o How is this a problem if the inks represent pollutants?”
o Ask visitors to consider how this is similar to and/or different from
local areas. Where in the community would there be the most
pollutants? o Ask visitors to identify where the rain, snow, etc. in their area
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drains. They may name local rivers streams, lakes, or bays, etc. Everything you ever nee ded to k now about watershe ds and
more:
What is a watershed?
A watershed is an area where all surface water drains into the same body
of water (river, lake, or ocean). Surface water consists of the tiny trickles
of water flowing on the surface of the Earth that develop into larger
streams and eventually combine to form rivers and lakes.
Rivers are organized into networks, each with its own recharge area
upstream, and drainage channel and mouth downstream. Networks are
ordered from ocean to main rivers to secondary rivers to streams, which
correspond to ocean watersheds, river watersheds, sub-watersheds, subsub-watersheds, and so forth. The boundary of a watershed is called a
watershed divide.
In a watershed, water flows from high to low, from upstream to
downstream. Watershed recharge is a function of precipitation, soil and
bedrock permeability, absorption of water in the soil by plant roots, and
evapotranspiration. As part of the latter process, plants return moisture
to the atmosphere by transpiration, and the water eventually returns to
Earth in the form of precipitation (for example, as rain, snow or hail).
The easiest way to describe the network of rivers and lakes on a smallscale map is to show the watersheds. In Canada, there is a detailed
hierarchy of watersheds, ranging from the largest (drainage into oceans
and their equivalents), down to the smallest ramification.
Locati on and Main Ri vers of Ocean Watersheds
The Pacific Ocean watershe d drains the area west of the Rocky
Mountains. The Fraser, Yukon and Columbia rivers are the largest rivers
draining this region. It is separated from all other drainage areas by the
continental divide. This is defined as the north-south line along the
western Cordillera that separates rivers flowing ultimately into the Pacific
Ocean from those flowing into other oceans.
The Arctic Ocean watershed is the area flowing directly into the
Arctic Ocean or into the channels of the Arctic Islands. Hudson Bay,
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James Bay and Ungava Bay are considered to be part of the Arctic Ocean
but for most purposes, their drainage area is usually considered as a
separate entity. The Mackenzie River dominates the Arctic Ocean
watershed.
The Hudson Bay watershed is a huge area that captures about 30% of
total Canadian runoff. Many of its river systems, such as the Nelson and
Churchill rivers (of Manitoba), drain eastward from the continental divide
to Hudson Bay. As well, many large rivers drain from the south and east
into Hudson Bay or James Bay. The extensive areas of drainage into
Ungava Bay and Foxe Basin are also considered to be part of the Hudson
Bay drainage area.
The Atlantic Ocean watershed is dominated by the Great Lakes–St.
Lawrence system, but there are other significant watersheds, such as
those of the Churchill River (of Labrador) and the Saint John River in New
Brunswick.
The Gulf of Mexico wate rshed occupies in Canada a
southern Alberta and Saskatchewan. The waters drain
Mississippi system, which ultimately drains into the Gulf
Gulf is part of the Atlantic Ocean but, because of the
often studied as a separate entity).
small portion of
south into the
of Mexico. (The
Mississippi, it is
Finally, parts of Alberta and Saskatchewan have closed watersheds or
areas of internal drainage: these are river systems that do not drain into
any ocean.
Physical Attributes of Watersheds
Watersheds contain not only rivers but also several other accessible
natural sources of freshwater including lakes, ponds, reservoirs,
groundwater aquifers, snow packs, glaciers, ice fields and, at the most
fundamental level, the liquid and solid precipitation that feeds and
replenishes all these sources.
The map layers show different physical components of a watershed. The
following descriptions of each layer demonstrate the importance of each
component to watersheds.
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Hydrological Components of Waters heds
Lakes and Rivers
There are a large number of interconnected and almost-connected lakes
and rivers that make up the Canadian drainage network. These lakes and
rivers are the legacy of the several advances and retreats of the
Pleistocene ice front, before which meltwaters were escaping by any
possible route, creating and abandoning drainage channels or simply filling
every depression on the ground.
The easiest way to describe the network of rivers and lakes on a smallscale map is to show the watersheds. In Canada, there is a detailed
hierarchy of watersheds, ranging from the largest (drainage into oceans
and their equivalents), down to the smallest ramification.
Rivers, which form extensive networks across the country, are natural
drainage channels for surface water. Surface water is received from two
major sources: runoff and base flow. Runoff is that part of precipitation
that flows toward the rivers or streams on the ground surface or within
the soil. Base flow is the part of stream flow that enters the stream
channel from groundwater.
Aside from glaciers, running water has had the most impact on shaping
the Earth's landscape. In addition to the rivers, Canada has a huge number
of lakes, the exact number being unknown.
A lake may be defined as any inland body of standing water, usually
freshwater, larger than a pool or a pond. Canada is famous for its number
of lakes. There are at least as many as two million lakes of all sizes
covering, in total, 8.9 per cent of the country. Also, Canada has 563 lakes
with a surface area greater than 100 square kilometres. A complete list is
given in the Facts about Canada section of The Atlas of Canada. The
largest set of lakes, the Great Lakes, straddle the Canada–United States
boundary, accounting for 18% of the world's freshwater in lakes.
The importance of lakes lies in their ability to store water during times of
plenty and release it gradually. Thus, lakes perform an extremely valuable
task in balancing the flow of the rivers on which they are located. For
example, the Saskatchewan River, with few lakes, has a maximum
recorded flow of 59 times its minimum flow. On the other hand, the St.
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Lawrence River, which drains the Great Lakes, has a maximum flow of only
twice its minimum flow. The difference in flow patterns in these two rivers
is partly due to precipitation differences, but results mainly from the vast
storage provided by the Great Lakes for the St. Lawrence River compared
with the negligible lake storage on the Saskatchewan River.
Groundwate r Aquifer
Groundwater is water found beneath the Earth’s surface and located
below the water table. In Canada, there is more water underground than
on the surface. Groundwater occurs in the tiny spaces between loose
materials on top of bedrock, or in cracks in the bedrock. The most
important concentrations are in aquifers, near the top level of the water
table.
The natural connections of groundwater to the surface are varied:
groundwater is interconnected with lakes and rivers, and it often also
emerges naturally as springs.
Groundwater is a vital component of Canada’s freshwater resource,
supplying a substantial proportion of municipal, agricultural and other
requirements for water. The origin and composition of aquifers are varied,
as are their uses. Some important examples are given below:
Many important Canadian aquifers are composed of thick deposits of
sand and gravel previously laid down by glacial rivers. These types
of aquifers provide most of the water supply for some large
municipalities, including the Kitchener–Waterloo region in Ontario
and the Fredericton area in New Brunswick.
The Carberry aquifer in Manitoba, west of Winnipeg, is an old delta lying
on what was formerly glacial Lake Agassiz. This aquifer is well
developed as a source of irrigation water.
Prince Edward Island depends on sandstone aquifers for its entire water
supply.
A major glacial outwash sand and gravel aquifer occurs in the lower
Fraser Valley in British Columbia. It is extensively used for municipal,
domestic and industrial water supplies.
The Winnipeg and Montréal aquifers, both of which are used for
industrial water supply, are composed of fractured rocks.
Wetlands
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Wetlands are lands permanently or temporarily submerged or permeated
by water and characterized by plants adapted to saturated-soil
conditions. Wetlands include freshwater and saltwater marshes, wooded
swamps, bogs, seasonally flooded forest, sloughs and peatlands — any
area of relatively shallow water that can keep water long enough (and still
enough) to let wetland plants and soils develop.
Wetlands are unique ecosystems and are vital components of the
hydrological regime. For example, they:
• modulate discharge regimes in rivers by reducing peak flow during
floods and maintaining flow in rivers during dry periods
• recharge groundwater aquifers
• act as reservoirs in the cycle of production, release and storage of
important greenhouse gases
• absorb, store and assimilate contaminants, such as heavy metals and
sulphur from acid rain, that enter them via precipitation, surface-water
flow and groundwater seepage
• serve an important remediation function because they permanently
break down many contaminants, such as nitrate
• provide habitat for fish and wildlife and for many unique types of plants
• provide many recreational opportunities, such as fishing, hunting and
bird watching
Glaciers and Icefields
Glaciers and icefields are huge masses of ice, formed on land by the
compaction and recrystallization of snow. They move very slowly down
slopes, or move outward due to their own weight.
Glaciers and icefields are only found in two regions of Canada — the
Western Cordillera and the mountains of the eastern Arctic — an
estimated area of 200 000 square kilometres, or about 2 per cent of the
country’s area.
A huge quantity of freshwater is frozen in these icefields and high
mountain glaciers. This frozen water plays an important role in the
western part of the country. In fact, glaciers exert a direct influence on
the hydrological cycle by slowing the passage of water through the cycle.
Like groundwater, glaciers are excellent natural storehouses of water. One
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form of release by glaciers is in sudden outburst floods called
‘jökullhaups’. Usually, the release is more gradual, with glaciers having
their highest rate of melting in the summer. Glacier-fed rivers, which
include many of the largest rivers in Alberta and British Columbia, reach
their peak flow during hot summer weather when other sources of water
in these regions may be scarce. They are, therefore, extremely important
to the relatively dry Prairie region as sources of water for irrigation,
electric power and communities located close to them.
Snow C over
Snow cover is important for several reasons. First, it represents a major
reservoir of water, which is released during the spring melt period.
Knowledge of how much water is contained in snow cover and the rate at
which it melts is critical information for flood forecasting, agriculture and
optimal management of water resources. Semiarid regions, such as the
Prairies and interior valleys of British Columbia, are especially dependent
on snowmelt runoff, which can supply in excess of 80 percent of annual
total runoff. So water levels are generally high after snowmelt and
decrease during the summer due to evaporation and evapotranspiration,
which are at their peak in the summer.
The quantity of snow received during the winter season directly affects
the seasonal and annual cycle of streamflow and water availability, and is
a key element for drought monitoring, forest fire potential, and flood and
flow forecasting.
Components Affecting Watersheds
Relief
Relief is an important controlling factor for rivers and their watersheds.
For example:
• Relief determines the continental divide, which is the line that separates
waters flowing to the east and west.
• The orographic effect of the mountains of western Canada enhances
precipitation on the windward side of the mountain range due to the
vertical lifting (and cooling) of moist air. This phenomenon has an
influence on the rain and snow received to feed lakes, rivers and
groundwater.
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• Glaciers that develop on high mountains have an influence on
streamflow during the summer.
• During winter, snow falling on vast flat terrains is blown away by the
wind. This causes uneven distribution of the water supply from one
area to another, thus creating differences in water availability between
areas.
Permafrost
Permafrost is defined as a state when the ground, whether soil or rock,
remains at or below a temperature of 0 degrees Celsius for a minimum
period of two years. Permafrost thickness ranges from a few decimetres
at the southern limit of the permafrost zone to more than 700 metres in
the Arctic Islands. Permafrost plays an important role in hydrology
through its influence on infiltration, runoff and groundwater storage and
flow.
Many wetlands in Canada owe their existence, at least in part, to cold
winters and the resulting impairment of drainage by the permafrost, as is
the case for many sub arctic and arctic wetlands.
Forests
The hydrological cycle consists of three major components:
• precipitation
• surface and subsurface water flow and storage
• evaporation from soil, vegetation, lakes, streams and oceans
•
Forests play a vital role in the hydrological cycle. In fact, the amount of
forest cover, health of the forests and their maturity influence the
patterns of evapotranspiration, soil moisture and rainwater transportation
into groundwater and surface water. Forests also filter air and water,
moderate climate, provide habitat for wildlife, stabilize soil and are an
important component of Canada’s economy, culture, traditions and
history.
Terrestrial Ecozones
Ecozones are broad ecological zones on the earth's surface that cover a
large range of ecosystems such as temperate forest, mountain ranges,
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grassland, taiga, arctic tundra, extensive river systems, coastline and
farmlands. Each ecozone has its own climate, relief, soil, flora, fauna and
distinct human activities. In Canada, there are 20 ecozones: 15 terrestrial
and 5 marine.
Each terrestrial ecozone contains several watersheds. Like an ecozone,
each watershed encompasses several types of ecosystems including
aquatic, waterside (lakeside, riverside, riverai n), forest, agricultural,
urban and wetlands.
Land Cove r
Each watershed is a component of the Earth. The land cover layer shows
the predominant land cover type present in each watershed such as
forest, shrublands, tundra, grasslands, and developed land types, including
cropland, mosaic and built-up areas and water.
Human Components of Watersheds
Canadians have a strong cultural link with water, which is a major facet of
our heritage, our spirituality and our economy. From the earliest
settlements, people built their homes along rivers and lakes.
Apart from being a source of drinking water, the water of watersheds is
used for irrigation, the production of hydroelectricity and as a means of
transportation. The riverbanks and floodplains provide aesthetically
pleasing sites for housing and recreational activities. Unfortunately, water
is also used as an egress for industrial discharge.
Major water consumers are municipalities, agriculture, mining,
manufacturing and thermal power generation. Consequently, there are
huge demands from these activities for all water reserves.
The map layers show different human and economic components of a
watershed. The following descriptions of each layer demonstrate the
importance of each component to watersheds.
Human Components
Popula tion
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The highest demand for freshwater arises from the southern areas of
Canada within 200 kilometres of the United States, where the population
density is highest. Many of the major river systems in the south, however,
flow northwards away from the major cities.
The rapid growth of population in southern areas has resulted in an
increasing gap between the availability of freshwater resources and the
demand from economic and human activities (such as municipalities,
thermal power generation, manufacturing, mining and agriculture).
Continued urban development causes stress on watersheds. It alters the
hydrological cycle by modifying the fluxes of water and sedimentation and
by decreasing the water quality, affecting the biodiversity and bringing a
general degradation of water resources. Also, groundwater recharge may
decrease due to decreased permeability of the aquifer and the overlying
materials. Compared to watersheds with little or no population,
watersheds in urban areas are subjected to changes in local
meteorological phenomena and microclimate, leading to increased
precipitation downwind of cities, higher incidence of fog and higher air
temperatures, which favour evaporation.
Growing urban populations also impose increasing demands for provision
of water services, including water supply, drainage and wastewater
collection and treatment. Also, the increased wastewater discharge that
results from this growth causes chemical and thermal pollution, a
decrease of oxygen, eutrophicati on, restrictions on fish and shellfish
consumption, degradation of aquatic and wildlife populations and their
habitat, beach closures and added costs to agricultural, industrial and
municipal users for treatment of water.
Aboriginal Population
Water for Aboriginal peoples is the basis of all life. For them, it is
necessary to understand and respect the water and its role. Knowing how
water can be used for nourishment and transportation can be life-saving
skills.
Aboriginal populations are profoundly linked to water and waterways for
both physical and spiritual health. Today, the water quality of many
watersheds is degraded by the pressures of human development. To
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many Aboriginal people, this degradation of the land and the water results
in the deterioration of their health and way of life.
Economic Components
Dams and Diversions
There are a number of dams and diversions in most provinces in Canada.
Water is stored behind a dam, and then withdrawn from its natural course
for transfer elsewhere in the same, or to another, drainage basin. Dams
and diversions redistribute the stream flow toward areas that have
greater demand.
The vast majority of large dams in Canada were constructed solely for
hydroelectric production. The others were constructed primarily for water
supply and for irrigation, mainly in the Prairie provinces, whereas others
serve a variety of purposes, including flood control, navigation, recreation,
or a combination of these. The more recent and largest dams are the La
Grande (James Bay) Project in Quebec, the Churchill–Nelson diversion in
Manitoba, and the Churchill Falls Project in Labrador, all publicly
administered hydroelectric power programs.
Hydro developments have had a substantial effect on rivers and lakes in
Canada. There have been relatively few large hydro sites developed since
the 1970s because the environmental and human effects to be avoided
or mitigated in such large projects make them increasingly difficult and
costly to plan and build.
Agriculture
As agricultural land use in Canada has increased, the natural hydrology of
watersheds has changed, affecting the relative availability, and in some
cases the quality, of water. Agriculture is one of the largest water
consumers and withdraws water supply from rivers, streams, reservoirs
and wells for land irrigation and watering livestock.
Irrigation is defined as the provision of water to crops beyond what is
provided by local rainfall. Irrigation is a vital part of agriculture in certain
areas of Canada, such as the southern Prairies and the interior of British
Columbia. The amount of water that needs to be withdrawn for irrigation
varies annually. It depends on winter precipitation and weather and soil
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moisture during the growing season. In fact, dry regions in the southern
Prairies and in the interior of British Columbia have severe moisture
deficits at some time during most summers. Dry areas are also more
prone to long-term drought conditions as well. These areas (especially
southernmost Alberta) hold most of the one million hectares of irrigated
cropland in Canada.
Forests
Forests play a vital role in the hydrological cycle, influencing patterns of
evapotranspiration, runoff and soil moisture. In fact, forest cover
maintains stability of the infiltration capacity of the soil, decreases runoff,
lowers wind speed and increases precipitation interception, thereby
significantly affecting the local microclimate and hydrological cycle.
Disturbances caused by forestry operations, fires and infestation,
however, exert significant impacts on stream flow, water quality,
sediment discharge and groundwater recharge. The removal of vegetation
produces short-lived, significant decreases in water losses through
evapotranspiration and decreases in precipitation interception, which
together lead to increase in soil water content in disturbed areas. Removal
of vegetation also increases the flow of water out of the watershed.
Mining
Large volumes of water are used by the mining and petroleum sectors for
extraction and concentration of metals and nonmetallic minerals,
extraction of light and heavy crude, and generation of the electricity
required for crushing ore, on-site processing, smelting, refining and other
aspects of treating resources to improve their properties. Demand for
water by the mining industry is limited and localized but becomes high
when associated refining, smelting and manufacturing operations are
considered.
Furthermore, the release of substandard water from abandoned mines is a
significant threat to freshwater availability in some watersheds of the
country.
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