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Home » Characteristics of Lakes » Drainage Basin Characteristics

    Introduction
    Drainage Basin Characteristics
    Lake Basin Characteristics
    Water Quality
    Biological Characteristics (Introduction)
    Biological Characteristics (Plants)
    Biological Characteristics (Invertebrates)
    Biological Characteristics (Fish)
    Biological Characteristics (Wildlife)
    References

Drainage Basin Characteristics

If each drop of water in a lake could tell its tale of how it got there, we would hear a multitude of stories! Some water falls as rain, snow or hail directly onto the lake; however, in all of Alberta, except for a few small areas in the extreme northwest and the higher elevations of the Rocky Mountains, evaporation exceeds precipitation. Therefore, most lakes in Alberta would recede and eventually dry up if their only source of water was direct rain or snowfall. Most water in a lake comes from rain or snow that falls on land areas around a lake, perhaps many kilometres away. This water may take one of several routes to reach a lake and may be part of the surface, subsurface, or groundwater runoff. A lake drainage basin or watershed includes all the land that contributes surface or subsurface runoff to that lake (Fig. 2). Groundwater may originate from areas far outside the drainage basin.

Whether the drainage basin is small or large, barren rock or rich soil, heavily forested or recently cleared, it is one of the most important features affecting the nature of a lake. The drainage basin has a very strong influence on the quality of water in a lake, and water quality has a strong influence on the algae, aquatic plants, invertebrates, fish and wildlife that inhabit that lake and affect our use and enjoyment.

 

Drainage Basin Borders

The border of a drainage basin is the drainage divide-the height of land around the lake. When a map of a drainage basin is drawn, as is shown in Figure 1 of each lake description in the Atlas, the border is determined by examining topographic maps. The term gross drainage area refers to the largest possible physical area that could potentially contribute surface runoff to the lake. Gross drainage areas include all other water bodies in the basin, areas that are referred to as dead storage, and areas that do not normally contribute water except in years of above-average runoff. The drainage area for each lake in the Atlas is presented as the gross drainage area minus the surface area of that lake.

Areas within a lake drainage basin that contribute runoff to that lake during an average runoff year are referred to as contributing areas. The size of the contributing area within a drainage basin can vary depending on the amount of runoff produced in a given year. Contributing areas can increase in size during years of above-average runoff when increased runoff volumes exceed the storage capacity within the drainage basin. Similarly, contributing areas can decrease in size during years of below-average runoff, when low-lying areas trap water that would ordinarily pass downstream. In the Atlas, the estimated amount of surface runoff is based on the estimated size of the contributing area within the drainage boundary in a year with average precipitation.

Dead storage areas are parts of some drainage basins where surface runoff cannot flow into the lake but becomes trapped in depressions that have no outlet channel to release water downstream, even during years of high runoff. Other low-lying areas that trap runoff and prevent it from contributing to flows downstream during years of average or below-average runoff are called non-contributing areas. Non-contributing areas have the potential to contribute water in above-average runoff years when the limited storage capacity is exceeded by the increased volume of runoff, but runoff generated within non-contributing areas or dead storage areas is not included when determining a mean annual (average year) water balance for a lake. However, water lying in dead storage areas may soak down into the ground, become part of the groundwater and so enter a lake. In the Atlas, the input of groundwater to a lake is not included in the values in Table 2 of each lake description.

 

Size of Drainage Basins

In Alberta, the size of lake drainage basins is extremely variable, from Lake Athabasca's enormous 282,000-km2 basin which covers more than half of Alberta and parts of British Columbia and Saskatchewan, to the tiny, 0.5-km2 drainage basin of Sauer Lake, one of the pothole lakes in the rolling hills west of Edmonton. The size of the drainage basin relative to the area of its lake is also highly variable. In the Atlas, drainage basins more than 20 times the area of the lake have been described as relatively large (for example, Crowsnest and Rock lakes), those 10 to 20 times the area of the lake are called medium-sized (for example, Elkwater and Beaverhill lakes) and those less than 10 times the area of the lake are called relatively small (for example, Sylvan and Pigeon lakes). The ratio of the drainage basin area to the lake area is an important factor influencing the water quality of a lake. Lakes with proportionately large drainage basins usually receive more runoff, so the lake level may be more variable. They also receive greater amounts of nutrients and suspended sediment than lakes with small basins.

Many of the water bodies discussed in the Atlas are reservoirs whose effective drainage basins may have been changed by the construction of dams and diversion canals. Reservoirs can be either onstream or offstream. Onstream reservoirs consist of a structure across a major stream or river that impounds all or part of the flow to store water until it is needed. The water supply for onstream reservoirs is generally provided by the natural drainage area of the river upstream of the structure. For example, the drainage basin for Ghost Reservoir is that of the Bow and Ghost rivers upstream of the Ghost Dam; the drainage basin of Gleniffer Lake is that of the Red Deer River upstream of Dickson Dam. However, in some cases, minor diversions may bring additional water from outside the natural drainage basin. For example, St. Mary Reservoir is an onstream reservoir on the St. Mary River but additional water is diverted to it from the Belly and Waterton rivers.

Off stream reservoirs consist of a structure across a minor stream or coulee and most of its water is diverted from a major source outside the natural drainage basin. The volume of water diverted can be very large and can contribute much more water to the offstream reservoir than is produced from the natural drainage area. Many of the reservoirs in southern Alberta are built in almost-dry coulees and water is brought to them from major rivers via a system of canals. For example, the natural drainage basin of Travers Reservoir provides only 3% of the water in the reservoir; 10% is brought via diversion from the Highwood River, and 87% is brought via diversion from the Bow River. Crawling Valley Reservoir receives less than 1% of its water from its natural watershed; more than 99% is diverted to it by canal from the Bow River. In the Atlas, the drainage basin size and the map of the drainage basin in each lake or reservoir description refer only to the natural drainage basin, and therefore exclude areas that may contribute water via canals. However, diversion canals are marked on the maps and their contribution is presented in the tables and discussed in the text.

 

Runoff: Measured and Estimated

Surface runoff refers to the precipitation that falls on a land area and eventually flows down slopes to gather in streams, lakes and other water bodies. When rainstorms are extreme, precipitation may completely saturate the surface soil layers and water will flow over the land surface, usually in brooks, streams or rivers. If surface runoff reaches a lake, it usually does so in a few hours or days after a rainfall or sudden snowmelt. The predominant nature of surface runoff, however, is not overland flow but rather subsurface flow made up of water that penetrates the upper soil horizons and flows laterally down the slopes before it seeps back to the surface in the lower regions of the slope. The amount of surface runoff can vary significantly, depending on topographic features and the balance between precipitation and evaporation in the drainage basin.

Surface runoff which flows within a watercourse is referred to as streamflow and can be measured by hydrometric gauging stations. Water Survey of Canada (WSC) and Alberta Environment have jointly established a network of hydrometric stations on individual streams throughout the province. The hydrometric network has recorded the flow of selected rivers and creeks over many years. The data from these stations were used to estimate the runoff from a monitored watershed and were also used to estimate the surface runoff of ungauged watersheds with similar physical and climatic characteristics.

Surface runoff estimates for the lakes in this Atlas are based either on data from a single representative gauging station or on a regional analysis of several stations in the area. Runoff for an average year (mean annual yield) is determined from available data and is usually expressed as a volume of water produced per unit area. The estimated mean annual yield is then multiplied by the contributing drainage area of a lake to estimate the expected inflow for an average year (mean annual inflow).

For example:

mean annual yield = 50,000 m3/km2
contributing drainage area = 100 km2
mean annual inflow = 50,000 m3/km2 x 100 km2
  = 5,000,000 m3

If there are other lakes in the drainage basin of the lake being discussed, then the runoff to them was estimated, the amount of evaporation from their surface was considered and the balance was considered as outflow which eventually entered the downstream lake.

Subsurface runoff consists of that part of the runoff which infiltrates the surface soils and moves laterally through the upper soil horizons toward the lake. The subsurface flow component moves much more slowly than surface flow and may contribute to the lake for many days or weeks after the surface flow has ceased.

Groundwater is that part of the runoff that has percolated deep into the ground. It may flow laterally to enter a lake under the lake surface. The groundwater component has a very slow response time and may contribute to a lake for many weeks, months or even years after a rainfall or snowmelt event. Groundwater is likely an important source of water for lakes in Alberta, but estimates have been made for only eight lakes in the Atlas: Narrow, Spring, Island, Tucker, Baptiste, Wabamun, Buffalo lakes and Long Lake near Athabasca. For these eight lakes, the groundwater contribution ranged from 4% to 49% (average of 18%) of the total water inputs. The greatest groundwater input was estimated for Spring Lake just west of Edmonton. The quality of groundwater may be quite different from that of surface inflows, partly because the area that contributes groundwater to a lake may be much larger and poorly related to the area contributing surface runoff. Although groundwater inputs (and outputs) may be important, they are difficult to quantify and they have not been included in the mean annual inflow values presented in the lake descriptions.

 

Biophysical Features of the Drainage Basin

The shape and depth of a lake is largely determined by the underlying bedrock and surficial deposits laid down during the ice age thousands of years ago. These features, plus the climate, soils and vegetation in the drainage basin all affect the quality of water in the lake, which in turn has a strong effect on the plant life, fish and wildlife that inhabit it and determine the water use and recreational potential of that lake.

Bedrock

Bedrock is the continuous layer of rock underlying the soil and unconsolidated surficial deposits on the earth. Some bedrock is sedimentary, formed by the sedimentation of silt and organic matter under seas and lakes; other rock may form as lava from volcanoes or from layers of volcanic ash, or it may form when layers of molten rock harden underground. Bedrock in Alberta is primarily sedimentary and consists of layers of sandstone, siltstone, shale, coal and limestone. In the eastern part of Alberta, bedrock strata are fairly flat, but in the western area it has been greatly shifted, folded, tilted and faulted by the formation of the Rocky Mountains.

The oldest bedrock underlying Alberta was first laid down in Precambrian times, beginning 3,500 million years before the present when most of Alberta was covered by an ocean inundating the land from the west. The repeated inundations and exposures across the ages of the land that is now Alberta are described in Table 2, as are comments regarding conspicuous biological features that occurred in the area. Figure 3 shows a cross-section of Alberta and indicates the present-day position of the bedrock strata. The bedrock formations underlying each lake and reservoir are presented in Table 1 of each lake description.

Surficial Deposits

The present configuration of the bedrock of Alberta was virtually fully established two million years ago. Since then, during the Quaternary Period, there were four ice ages when huge ice caps formed in the Arctic regions and began to flow southward over large areas of Eurasia and North America. The first three advances of ice were located around Hudson Bay and spread outward and southward as far as the confluence of the Ohio and Missouri rivers. The ice flowed westward across Saskatchewan and may have crossed what is now Alberta's boundary; however, until about 35,000 years ago, most of Alberta remained an ice-free corridor.

Finally, in the last great glaciation, called the Wisconsin, sheets of ice up to 1,600 m thick began to grind across Alberta from the east and north. At the same time, another ice sheet massed in the Rocky Mountains and flowed eastward to coalesce with the ice sheet from the north. The two sheets then flowed southward, parallel to the Rocky Mountains, until all of Alberta was under ice except for high mountain peaks, the highest parts of the Cypress Hills and patches of the Porcupine Hills.

As the ice sheets advanced and retreated over Alberta, they sculptured the land, carving and eroding the mountains, moving rocks and depositing gravel and silts until the landscape was virtually as we see it today. The last retreat of the ice, beginning 12,000 years ago, left behind enduring impressions on Alberta. As the ice sheets melted and retreated, they left a blanket of glacial till up to 100 m thick over most of Alberta east of the mountains. In southern Alberta, the till forms a ground moraine, leaving a gently undulating surface. Water drains into gentle depressions to form shallow lakes like Eagle and Tyrrell lakes. In central Alberta, the terrain is more hummocky and rolling; examples are found around Red Deer, from Elk Island National Park to Cooking Lake and west of Stony Plain. In some areas, large blocks of ice were left by the retreating glacier and till piled up around the ice so when the ice melted, holes, or kettles, were left in the landscape. Small lakes fed and drained by groundwater now fill these kettles; examples are Spring, Eden and Hubbles lakes. In some areas, glacial till blocked preglacial channels, impounding water to form lakes like Crowsnest, Rock and Baptiste.

As the glaciers melted, they produced huge volumes of meltwater, which cut through the till plain and formed long, steep-sided, flat-floored river valleys. Many of these valleys are now dry, or nearly dry. An example on the southern prairie can be seen where Verdigris, Etzikom, Chin and Forty Mile coulees are part of one series of meltwater channels. A number of these channels are now dammed to form offstream storage reservoirs, for example, Milk River Ridge, Crawling Valley, Chin and Forty Mile Coulee reservoirs. Another conspicuous meltwater channel is now followed by the Battle River and includes Driedmeat and Coal lakes. Examples of lakes in smaller meltwater channels in northern Alberta include Long (near Athabasca), Narrow, Long (near Boyle) and Amisk lakes.

Ecoregions

Ecoregions are a classification of the natural zones within Alberta that are defined primarily by geographic and climatic features. The geography and climate subsequently affect the vegetation able to grow in an area, which in turn affects the soils that develop.

An ecoregion was defined in 1969 by Lacate as "an area characterized by a distinct climate as expressed by vegetation." The ecoregions of Alberta were recently mapped by Strong and Leggat (1981) of the provincial government and are shown in Figure 4; their features are summarized in Table 3. Much of the foothills and northern parts of the province have been mapped in detail by the provincial government; reports on these areas were used to describe the drainage basins of several lakes in the Atlas, for example, the Kananaskis Lakes, Chain Lakes Reservoir and Gleniffer Lake. Soil surveys done by the Alberta Research Council present detailed mapping of the agricultural areas of the province, and these surveys were used to describe the soils and terrain of the basins of many lakes in the Atlas.

In general, the southeast part of the province is warmer, has lower precipitation and higher evaporation rates than the rest of the province. Three grassland ecoregions are found there. The Short Grass Ecoregion is the most arid, and the natural vegetation is mostly grama and spear grass. There are few natural lakes in this ecoregion but the naturally rich soil and warm climate have led to high demand for irrigation water. Several offstream reservoirs have been built in this ecoregion, including Crawling Valley, Little Bow Lake and Lake Newell reservoirs. Forming an arc around the Short Grass Ecoregion is the Mixed Grass Ecoregion, which supports natural vegetation of spear, grama and wheat grasses. There are also few natural lakes in this area, and most water bodies are offstream reservoirs for storage of irrigation water. Examples include McGregor Lake, Travers Reservoir and Tyrrell Lake (Fig. 5). The Fescue Grass Ecoregion curves around the Mixed Grass Ecoregion; rough fescue and Parry oat grass are the dominant natural plants. One of the few natural lakes in this area is Eagle Lake; most water bodies are irrigation reservoirs including tiny Chestermere Lake and large St. Mary Reservoir.

The slightly wetter and cooler area of central Alberta falls within the Aspen Parkland Ecoregion. Typified by groves of trembling aspen, it is divided into two subregions. The Groveland Subregion is in the southern and eastern portion where the climate is drier than to the north and west. Fescue grasslands dominate and aspen groves occupy only about 15% of the area, occurring where moisture is available such as in depressions, in coulees and on north-facing slopes. The Aspen Subregion is the northern and western portion where dense forests of trembling aspen are interspersed with small areas of fescue grassland. The Aspen Parkland is one of the most productive farming areas of Alberta, and much of it has now been cleared and plowed. Natural lakes are fairly numerous in this ecoregion, including Beaverhill, Buffalo and Pine lakes. The location of the Aspen Parkland between the dry grasslands and moist boreal areas results in quite variable amounts of runoff from year to year. This is reflected in lake water levels which exhibit fairly wide natural fluctuations. To combat the variability in water supply, several dams or weirs have been built to stabilize flows in rivers and creeks, including a dam on Chain Lakes Reservoir, and weirs on Coal and Driedmeat lakes. Other lakes have weirs in an attempt to stabilize their water levels, for example, losegun Lake. Three others, Gull, McLeod and Lac St. Cyr, have water diverted into them to stabilize their levels.

If one were to travel from the prairie up into the mountains in the southern part of the province, one would encounter several ecoregions. At lower elevations in some southern areas is the Montane Ecoregion, which is typified by Douglas fir trees. Examples of lakes in the Montane Ecoregion are Beauvais and Crowsnest lakes and Ghost Reservoir. Higher up in the mountains is the Subalpine Ecoregion which supports lodgepole pine and Engelmann spruce as the dominant vegetation. Lakes in this ecoregion include the Kananaskis Lakes, Rock Lake and Spray Lakes Reservoir. The highest area is the Alpine Ecoregion where the climate is too harsh for tree growth and vegetation is limited to heaths and shrubby willows. Rocky peaks are barren of all vegetation and glaciers top many mountains. No alpine lakes are discussed in detail in the Atlas, but runoff and glacial meltwater from the Alpine Ecoregion provide inflow to several lakes and to most of the large onstream reservoirs such as Ghost and St. Mary reservoirs and Gleniffer Lake.

West from Calgary and north and west from Edmonton are the boreal group of ecoregions. The Boreal Mixedwood Ecoregion lies north of the Aspen Parkland and covers most of the northern half of the province. This region has higher precipitation and lower evaporation rates than the grasslands or parkland ecoregions. The result is a forest cover of trembling aspen and balsam poplar, and a relative abundance of water. Consequently, the region is dotted with lakes, including large ones like Athabasca, Cold, Utikuma, Peerless and Lesser Slave; medium-sized ones like Wabamun, Pigeon, Cooking, Miquelon and Beaver and small ones like Sauer, Eden, Hasse and Twin (Fig. 6).

The Boreal Foothills Ecoregion is in the northwest corner of the province and continues southward along the foothills to a point just southwest of Calgary. This region supports a wide variety of tree species; the dominant species in any location varies from trembling aspen and balsam poplar to lodgepole pine, and white and black spruce. Lakes in this area include Buck and Crimson lakes in the south and Moonshine and Musreau lakes to the north near Grande Prairie. There is also a small patch of this ecoregion ringed by Aspen Parkland in the Cypress Hills in southern Alberta. Elkwater and Reesor lakes are in this area. The Boreal Uplands Ecoregion lies along the upper foothills north of the Bow River. Trembling aspen and white spruce are the dominant tree species. Lakes in this area tend to be small. There is little information on lakes in the Boreal Uplands Ecoregion and no lakes in this ecoregion are included in the Atlas.

The Boreal Northlands Ecoregion is found on high plateaus and hills in the northern part of the province. The most abundant trees are trembling aspen and white spruce. There are beautiful lakes in this region, including Gardiner, Namur and Swan, but because the only access to these lakes is by air, little information has been collected on them. In the Atlas, only the north shore of Lake Athabasca lies in this ecoregion.

The cold Boreal Subarctic Ecoregion supports black spruce and Sphagnum moss. Permafrost underlies much of this ecoregion. There are numerous lakes, but little is known about them. No lakes from this ecoregion are included in the Atlas.

Soils

The soils around a lake and in its drainage basin have an effect on the lake by contributing nutrients and by influencing the rate of runoff from the land into the lake. Soils that occur in the drainage basin are discussed in each lake description in the Atlas. Information regarding soils was usually derived from the soil surveys done by the Alberta Soil Survey (Alberta Research Council and Agriculture Canada Soil Survey Unit) for areas of the province where agriculture is the primary land use. Ecological Land Classification and Evaluation Reports prepared by Alberta Forestry, Lands and Wildlife (formerly Alberta Energy and Natural Resources) provided data on soils in the foothills, mountain and northern portions of the province.

There are seven major groups of soils in Alberta: Chernozemic, Luvisolic, Brunisolic, Regosolic, Gleysolic, Organic and Solonetzic.

Chernozemic soils develop under grasslands on a wide variety of parent materials in well-drained to imperfectly-drained sites. Brown Chernozemic soils are found where there are short grasses and severe moisture deficiency; Black Chernozemic soils occur in less dry areas. Chernozemic soils are usually excellent for agricultural production.

Luvisolic soils develop on a wide variety of parent materials under mixed deciduous-coniferous forests. They are generally found in imperfectly-drained to moderately well-drained sites.

Brunisolic soils develop on imperfectly drained to well-drained sites on various types of parent material. They develop under coniferous or deciduous forests.

Regosolic soils occur in a wide variety of ecological conditions where natural disturbance has inhibited the development of soil horizons. They are common near river beds, on colluvium, on steep and actively eroding slopes and on shallow parent material over bedrock in the mountains.

Gleysolic soils occur in areas of poor drainage where there is prolonged inundation or a high groundwater table.

Organic soils occur in areas of extremely poor drainage. They form by the accumulation of dead organic material such as sedge or moss peat.

Solonetzic soils develop on saline parent material in imperfectly drained to moderately well-drained sites. They form under grassland vegetation, usually in association with Chernozemic soils.

A drainage basin's soils affect a lake by influencing the rate of runoff and the amount and proportion of various nutrients and ions that move from the soils to the lake. However, little research has yet been done in Alberta to directly link the soil types present in the basin to the chemical composition of the receiving lake.

 

Land Use

The use of the land in a drainage basin has a direct bearing on the quality and quantity of water entering a lake. As discussed in the Water Quality section, the quantities of nutrients such as phosphorus transported from a hectare of urban land are several times that transported from a hectare of cleared or crop land, which in turn are several times greater than nutrient quantities transported from a hectare of forest. The rate that water runs off cleared land is faster than from forested land, so lake level patterns may change as forests are cleared. The distribution of forest/bush and cleared or open areas is marked on the drainage basin map for each lake. Data were taken from National Topographic Series maps, usually at 1:50,000 scale, and air photos taken since 1980 were used to update this information. Alpine areas and glaciers are also marked on the drainage basin maps, as are recreation, residential and urban areas. The major land uses in each drainage basin are discussed in the individual lake descriptions.

The increase in Alberta's population over the last 80 years has had a definite effect on the drainage basins of most Alberta lakes. As settlers came to Alberta, more and more land was cleared for crop production, pasture and intensive agriculture such as feedlots. Increased population also brings increased pressure for recreation, and cottages spring up around lakes. With the cottages comes more cleared land, problems of appropriate waste disposal, and fertilized lawns sloping toward the water-all of which may increase nutrient input to lakes. To protect popular lakes from degradation and inappropriate development, Alberta Environment established the Regulated Lake Shoreland Development Operation Regulations in 1977. These regulations prohibited further development on 15 lakes until a lake management plan and an area structure plan were prepared for each lake and adopted by the local municipalities. Area structure plans suggest ways to minimize environmental impacts and conflicts in lake uses.

Most of the development around lakes is recreational, especially in central Alberta where lakes such as Sylvan, Pigeon, Wabamun, Pine and Chestermere are fairly densely ringed by cottages and resorts. Commercial and industrial uses do not exert a major influence on most of the lakes in Alberta. Some of the lakes in the Cold Lake area, including Ethel, Wolf and Muriel lakes, provide water for heavy oil extraction. McLeod Lake also provides water for the oil industry, and Wabamun Lake supplies cooling water for a coal-fired generating plant. The reservoirs built in the mountains and foothills (Spray Lakes, Minnewanka and Ghost) are managed for hydroelectric power generation, whereas the irrigation reservoirs such as St. Mary, Milk River Ridge and Crawling Valley reservoirs are managed to supply water during the growing season. Logging in the foothills and northern areas of the province has removed forest cover in some drainage basins, as has strip mining for coal, especially in the Wabamun Lake area and in the foothills near Grande Cache and Cadomin.

J.M. Crosby

 

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