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

Lake Basin Characteristics

A lake basin is a water-filled bowl or depression in the surface of the landscape. With few exceptions, the lakes we now see in Alberta were formed when the last Pleistocene ice sheet retreated from Alberta about 12,000 years ago. As the glacier retreated, large collections of rock debris, called moraines, formed basins or dammed meltwater channels, and new lakes were born. In some areas, large blocks of ice were trapped in the outwash material or in the moraines that were left as the glaciers retreated. These ice blocks may have taken hundreds of years to melt. When they did, they left large holes in the blanket of glacial till. Some of the holes filled with water to form kettle or "pothole" lakes like Dillberry, Sauer and Eden (Fig. 7). Other lakes, such as Rock, Baptiste and Crowsnest, were formed when preglacial river valleys were dammed by moraines. Lake Athabasca was formed when movement of the glacial ice sheet scoured pre-existing valleys.

In areas where there are few natural lakes but a need for water storage, new lakes, called reservoirs, were built when dams were constructed across river valleys or coulees (Fig. 8). Reservoirs are similar to lakes in many ways, but their water level usually fluctuates more widely, and often the quantity of water flowing through them in a year is higher.

Lake Basin Morphology

Alberta lakes and reservoirs vary considerably in their size, shape, bottom form and depth, or morphology. To a large extent, the origin of the lake basin determined its present-day shape and depth. Many of the depressions left by the retreating glacier are shallow and wide, and therefore lakes formed in them are relatively shallow, such as Buffalo and Beaverhill lakes. Kettle lakes may be deep for their small size, and lakes in preglacial valleys also may be quite deep. Those formed in meltwater channels tend to be long and narrow, such as Battle, Narrow and Amisk lakes. The shape of the lake bottom is also influenced by events that have occurred since the last glacier retreated. For example, a lake with a large watershed, high productivity or a large inflow may have filled in considerably over the past 12,000 years. In contrast, lakes with small watersheds, low productivity and only intermittent inflows, such as Hubbles Lake, are likely to have a thinner layer of bottom sediments. The bottom sediments in Wabamun Lake are nearly 16-m thick in the centre of the basin, and most of this material eroded from the watershed over these years. The lake may not have been much deeper at one time, however. Evidence from core studies suggests the lake has gone through periods of both high and low water levels, depending on the climate at the time. Pollen analysis from other lakes, including Moore, shows that the climate was warmer and lake levels were generally lower between 9,000 and 4,000 years ago than during the last 4,000 years.

The morphology of a lake has a great influence on its ecological characteristics. A description of the lake's size, shape, depth and volume is fundamental information for the lake scientist, and is of interest to anglers and other lake users as well. Such information is best obtained from a map of the depth contours of the lake bottom, or bathymetric map. During a bathymetric survey, personnel in a boat or on the ice in winter measure depths along numerous transect lines that stretch across the lake from shore to shore (Fig. 9). For small lakes, depth may be measured simply with a weighted measuring line, but most modern surveys use sonar equipment to record depth continuously along the transects. No matter how depth is measured, it is essential that the precise location of all depth measurements are known so that they may be accurately plotted on an outline map of the lake. For small lakes, simple survey equipment on shore or in a boat may be used to position depth measurements. However, for large lakes, modern surveys are conducted with shorebased electronic positioning systems that determine the position of the boat at all times, even at varying speed and wind drift. All bathymetric maps have some limitations. Depths are recorded along transects that are usually no closer than 100 m, and may be considerably farther apart on large lakes. Therefore, the point of maximum depth may be missed, or small mounds or other irregularities on the lake bottom may not be recorded. In addition, the depths indicated on the map were recorded at the water level on the date of the survey. If the water level has changed since then, the depth must be adjusted accordingly. For lakes in the Atlas, the bathymetric maps constructed since about 1978 most accurately represent their bottom contours.

To construct the bathymetric map, selected depths (for example, 2, 4, 6, 8 and 10 m) are interpolated from field measurements and the interpolations for each depth are connected by continuous lines, which represent depth contours. The area of the lake is determined with a planimeter, a device that calculates area or distance as it traces a contour line. Volume or capacity may then be calculated from the area of each depth contour and the height of the water stratum between successive contours (Fig. 10). The total lake volume is the sum of the volumes of each stratum.

Once the area and capacity are determined, area/capacity curves are drawn. They are used to estimate a new area and volume if the level of the lake should change, or they may be used to estimate the area of a portion of the lake at a certain depth, such as the area of aquatic plant growth. Most of the area/capacity curves for lakes in the Atlas are accurate only for elevations below the geodetic or assumed elevation of the water on the date the bathymetric survey was made.

The mean or average depth of a lake is calculated by dividing the lake's volume by its area. The mean depth is one of the best indicators of the morphology of a lake, and it tells a great deal about its limnology or water quality characteristics as well. If the mean depth is shallow, the lake water will mix from the surface to the bottom on windy days. The bottom sediments may be a source of nutrients, which will enhance productivity, potentially reduce dissolved oxygen levels, and thereby contribute to the risk of winterkill or summerkill. For example, the mean depth of Cooking Lake is 1.7 m and that of Driedmeat Lake is 2.2 m; both are highly productive. Cooking Lake cannot sustain game fish populations, and Driedmeat Lake also winterkills frequently. On the other hand, lakes that have a deeper mean depth may rarely or never winterkill, even though they are eutrophic or productive. Examples are Pinehurst Lake (mean depth of 12 m) and Amisk Lake (mean depth of 15.5 m). Of all the lakes discussed in the Atlas, Cold Lake has the greatest mean depth (50 m) and is one of the least productive.

A comparison of mean and maximum depths provides information on the shape of the lake. For example, Crimson and Spring lakes have relatively deep maximum depths (9.1 m for both), but shallow mean depths (2.2 and 1.9 m, respectively). These lakes have very small deep areas, but large areas of shallow water. A large ratio may also result when there is a deep, small basin attached to a large, shallow main basin, as in Island Lake (maximum depth of 18 m, mean depth of 3.7 m). Three-quarters of the lakes and reservoirs in the Atlas have maximum depths that are less than 3 times the mean depth. Lake Athabasca has the greatest depth relative to mean depth (ratio of 6).

The shoreline length is also useful for describing the morphology of a lake. It is measured on the map of the lake by tracing the shoreline, or intersection of the land and water, with a map-measuring wheel or an electronic planimeter. Lakes or reservoirs with long shorelines compared to their area would be those with many bays, peninsulas and islands. Reservoirs formed in stream or meltwater channels with many side channels often have very long shorelines relative to their area. Examples include Crawling Valley, Travers and St. Mary reservoirs. Those with the shortest shorelines relative to area are round, with little or no development of bays. The most perfectly round lakes in the Atlas are tiny Twin Lake and large Calling Lake.

The Lake Bottom

The lake bottom is covered in a layer of mud called sediments, the soil of the lake (Fig. 11). This material contains organic matter (decomposing plants and animals), mineral matter like clays and carbonates that would be found also in soil, and inorganic material derived from plants and animals, such as the glasslike skeletons of diatoms. These sediment particles may originate within the lake, wash in from the surrounding land or settle from the air. Suspended sediment particles that are carried into the lake by streams quickly settle out once they reach the quiet water of the lake. Thus, the lake acts as a trap for soil particles, nutrients, organic material or pollutants originating in the watershed. The finest sediments are resuspended by wave action near shore, and gradually move toward the deepest areas of the lake. Over time, there is a greater accumulation of bottom sediments in deep water than in shallow water near shore. Even in productive lakes, such as Wabamun, Buck and Pigeon, a firm sand bottom may be present in the shallow water if it is exposed to wave action. But within stands of emergent vegetation or along shorelines protected from wind, the surface of the sediments is loose and yellowish-brown. Below this surface layer, the sediments may be dark greenish-gray and have an unpleasant odour.

In areas of the lake bottom where there is sufficient light penetration and other conditions are suitable, rooted aquatic plants will grow. The littoral zone extends from the shoreline to the greatest depth that plants will grow in a particular lake; light penetration is usually the most important factor that determines this depth. The depth of the littoral zone has been measured in several Alberta lakes during plant surveys conducted from 1978 to 1984 by Alberta Environment. For example, the littoral zone extended to 3.5 m in highly productive Baptiste and Nakamun lakes, 4 m in moderately productive Lac St. Cyr and Skeleton Lake, and 5 m in less productive Ethel Lake. The deepest recorded growth of aquatic plants during these surveys was 7 m in Muriel Lake, the lake with the clearest water of the lakes surveyed at the time. The depth of the littoral zone has not been measured for many lakes in the Atlas. However, University of Alberta researchers have developed a formula to predict this depth from a measurement of the lake's transparency (see Section 1, "Estimate of depth of the littoral zone in a lake", in the Appendix).

Water Balance

The volume of water in a lake changes in response to the quantity of water that enters and leaves it over a given period of time. An annual water balance for a particular lake is calculated by adding all of the inflows over a year, and subtracting the outflows, including evaporation. If the water level in the lake at the end of the year is different from that at the beginning of the year, the change in volume of water that this fluctuation represents must be included in the annual water balance.

Water enters a natural lake through direct precipitation onto the lake surface, runoff from the surrounding land and groundwater inflow. Reservoirs often have an additional input of water, as a diversion from another basin. Water is lost from a lake through evaporation (including evapotranspiration, the loss of water from the leaves of aquatic vegetation) and surface or underground outflow (see Fig. 2).

Both precipitation and evaporation were calculated with data obtained from Environment Canada climatological stations closest to the lake. The average annual amount of precipitation that falls in the area (reported as depth in millimetres) may be multiplied by the surface area of the lake to obtain the total volume of water that enters by direct precipitation. The rate of evaporation for a particular location was not measured directly, but was calculated from data on sunshine, temperature and relative humidity with an equation developed by Environment Canada. The loss of water by evapotranspiration has not been estimated for any lake in the Atlas, but it is likely to be significant only for small lakes with large areas of emergent vegetation.

Water also enters and leaves a lake over the surface of the surrounding land. Rain or snow falls in the drainage basin and gathers in streams or moves directly toward the lake within soils (subsurface flow). Only a portion of the precipitation that falls in the basin finds its way to the lake. Reservoirs may have additional inflows via canals. The total inflow volume reported in each lake description is based on estimates of annual runoff depth measured at stream gauging stations nearest the lake. Inflow and outflow are measured directly on most reservoirs, and outflow is also measured on some lakes. There is rarely more than one outlet on a lake, except where people have altered outflows or constructed diversions. If a lake originally had more than one outlet, differential erosion and cutting of the sill over hundreds of years would allow one to take precedence over the other. Reservoirs often have two or more outlets - one to maintain flow in the creek or river downstream of the reservoir, and the others to supply water for irrigation, power generation or other needs. Examples are Travers, St. Mary and Spray Lakes reservoirs.

Lakes may be part of groundwater flow systems. Water may enter and leave a lake underground, via bedrock aquifers and porous lenses within surficial materials. But the groundwater exchange with a lake is difficult to quantify, and therefore groundwater-lake interactions have been studied on only a few Alberta lakes. Detailed groundwater studies have been carried out by researchers at the University of Alberta on three lakes in the Atlas: Baptiste, Wabamun and Narrow lakes. In these studies, groundwater was estimated to contribute 13%, 5% and 30%, respectively, of the total water input. The first two studies were based on detailed simulation models, the latter was based on several different techniques, which included measurements made in the lake with devices called seepage meters, a detailed water balance and computer models. Within-lake measurements of groundwater input have been made at Buffalo, Spring, Island, Long (near Athabasca) and Tucker lakes by University of Alberta researchers. The average estimate was 19% of total water inflow, with values extending from 4% to 49%. In the two cases where groundwater inflow has been estimated from both detailed models and within-lake measurements, the results were very comparable in Baptiste Lake (13% and 11 %), but less similar in Narrow Lake (30% and 16%). For some lakes, the outflow of lake water into groundwater systems may be an important component of the water balance. For example, studies conducted on Wabamun Lake for Alberta Environment suggest that a large volume of water (40% of total annual outflow) must leave the lake underground, otherwise the lake water would be more saline than it is due to concentration of salts by evaporation.

Data on inflows, outflows and volume for a particular lake may be used to calculate a water residence time, or the average time required to completely replace the total volume of the lake with inflowing water, less evaporative losses. To calculate water residence time, the average total volume of the lake is divided by the average annual calculated outflow (precipitation plus runoff from contributing areas of the watershed minus evaporation). For most lakes in the Atlas, groundwater exchange was not considered in this calculation because information was lacking. No attempt was made to estimate residence times beyond 100 years. Many lakes in Alberta have very long residence times. For example, 40% of the natural lakes described in this Atlas have water residence times that exceed 50 years. Compared to most lakes, reservoirs have short water residence times, because their outflows are large relative to their volume. For example, the residence time of Ghost Reservoir averages 22 days over the year, but it can be as little as 10 days at times of high flow in the Bow River. The average residence time for all reservoirs described in the Atlas is two years.

Water Levels

Water levels are measured on many lakes in Alberta by the Water Survey of Canada (Environment Canada) or the Survey Branch of Alberta Environment under the terms of the federal-provincial hydrometric cost sharing agreement (1985). The data points chosen for each water level graph in the Atlas include the minimum and maximum level for each year, and several additional high and low points to fill out the annual trend. Also, for a few reservoirs, mean monthly water levels were plotted to depict the seasonal variation in these water bodies. If the amount of water leaving a lake by evaporation, the outlet creek and groundwater is equal to the amount of water entering the lake as precipitation, runoff and groundwater, the water level or lake elevation will remain constant. But water levels are never constant in lakes, because they are influenced by numerous natural forces-wind, sun, rain, snow, beaver activity and changes in the water table-so they fluctuate naturally. Short-term water level fluctuations are dependent on whether a particular season is wet, dry, or average. A decline or increase in water level may continue for several consecutive years, depending on the predominant weather patterns. Over the period of record for most lakes, however, the water level shows neither a downward nor an upward trend (Fig. 12).

Some Alberta lakes have no permanent inlet or outlet creeks. Gull, Garner and Dillberry lakes are examples. The water level in these lakes is controlled by a balance between precipitation, diffuse or subsurface runoff, groundwater inflow/outflow and evaporation. Sometimes these closed lakes gradually decline in lake elevation, as have Gull and Miquelon lakes, although the reason for the decline has not been determined.

Lakes attract people, and there is a natural inclination to build houses, cottages and farms near them. But the natural fluctuation of a lake's water level may frustrate lake users-high water may flood property or low water may expose mudflats and inhibit recreation. One approach is to attempt to control the level of the lake with a weir, or small dam, on the outlet creek. Such lakes are called regulated lakes. But even with a control structure on the outlet, lakes will continue to fluctuate to some extent because the rates of evaporation and precipitation largely control water level in many lakes. During years of low precipitation, there may be insufficient water entering a lake to offset evaporation, and the lake level will decline in spite of a weir. Similarly, during years of excessive precipitation, the level may temporarily rise above the level of the artificial outlet. For large lakes with small outlets, the time required for water to run out of the lake may be several weeks or months, and there is little that can be done to relieve flooding during that time.

For most regulated lakes in Alberta, the new elevation after the weir is built is not greatly different from the natural one, usually less than 1 m higher, and rarely as much as 3 m higher. In some lakes, the sill of the weir may be adjusted by adding or removing stop-logs or by opening gates. Weirs in Alberta are usually made of driven piling and sheet steel, concrete or packed earth and clay (Fig. 13). Twenty-two lakes in the Atlas have weirs, including Coal, Driedmeat, Pigeon, Steele, Thunder, Beauvais and Buck. The Kananaskis Lakes are rather a special case as substantial dams were built on both lakes by TransAlta Utilities Corporation to store water and to manage the outflow for electric power generation. The water level of both lakes was raised over 10 m by these structures, but they are regarded as regulated lakes rather than reservoirs because they were naturally large, deep lakes and their size was not greatly changed.

Sometimes the inflow to a lake is modified to further stabilize the water level. Streams from neighbouring drainage basins may be diverted into a lake; for example, Kent Creek is diverted into Lower Kananaskis Lake. Water may be pumped into a lake, such as the diversion from the Blindman River to Gull Lake and from the North Saskatchewan River to Lac St. Cyr.

When a weir is built on the outlet of a lake, even if it is only 1 m high, the outflowing water usually falls in a single cascade, and upstream fish movement is blocked. This is a particular problem in Alberta east of the foothills where the main sport fish is northern pike-a species not renowned for its jumping ability! To overcome this problem, Fish and Wildlife Division, Alberta Environment and the University of Alberta have designed and tested various types of fishways. The most common one is the step-pool fishway: instead of one large cascade, a series of pools are built, each separated by a small cascade that can be negotiated by northern pike. Regulated lakes with weirs and step-pool fishways include Driedmeat, Sturgeon, Steele, and Gregoire lakes. Another fishway, the Denil II, is built as a long, sloping chute with interior baffles to slow the flow of water (Fig. 14). Denil II fishways can be found on Lesser Slave and losegun lakes.

Reservoirs

In southern Alberta, where precipitation is abundant in the mountains but scarce on the prairies, reservoirs have been built to store water for various purposes. A reservoir is created when one or more dams are built to block the natural flow of water or to impound water that is imported into a basin. As a general guideline, a weir impounds a proportionally small amount of water compared to natural conditions and the water body it controls is called a regulated lake; a dam is a larger structure that impounds a proportionally large amount of water and the water body it creates is called a reservoir.

The reservoirs in Alberta can be divided into two types based on the source of water: onstream and offstream. Onstream reservoirs are those created when a dam is built across a river; most of the water in the reservoir comes from that river. Examples of onstream reservoirs are Gleniffer Lake, which was created by Dickson Dam across the Red Deer River; Ghost Reservoir, which was created by Ghost Dam across the Bow River below its confluence with the Ghost River; St. Mary Reservoir, which was created by St. Mary Dam built across the St. Mary River (Fig. 15); and Glenmore Reservoir, which was created by Glenmore Dam across the Elbow River. Onstream reservoirs are usually long and narrow, and the bottom slopes gently from the shallow inflow end toward the deep end near the dam. A delta often forms at the inflow end. The volume of water flowing through onstream reservoirs is usually large, and therefore the exchange of water is rapid. Reservoirs are designed to be filled to a specific level of water under normal conditions. The full supply level or FSL is the maximum level that the reservoir normally attains. Water is released from most onstream reservoirs at all times to maintain flow in the downstream portion of the river. Flow is either passed through turbines in the dam, through a spillway or if flows reach flood proportions, over an emergency spillway.

There are three general functions for onstream reservoirs in Alberta: hydroelectric power generation, irrigation water storage and flow regulation. The power generation reservoirs are in the mountains and foothills where the slope of the river is greatest. The reservoirs are filled to capacity in late fall, and water is released through the turbines to meet daily peak power demand through the winter. These reservoirs begin to fill again with spring runoff, but the water level is usually kept below the full supply level to save some storage capacity for flood protection. Some water is released all summer to meet daily peak power demand and to maintain flow in the river downstream. Examples of reservoirs used primarily for power generation include Spray Lakes and Ghost reservoirs. Onstream reservoirs built for the storage of irrigation water or water for municipal use tend to be in the lower foothills regions. They are filled in spring, then drawn down to meet demand-in summer for irrigation water, and all year for municipal use. Examples of onstream water supply reservoirs in the foothills are St. Mary and Glenmore reservoirs. An example of an onstream water supply reservoir on the prairie is Blood Indian Creek Reservoir southeast of Hanna. Onstream reservoirs built to allow management of downstream flow, such as Gleniffer Lake on the Red Deer River, store water in spring and summer and then release it to augment winter flow to meet downstream demands or to relieve problems of low dissolved oxygen concentrations. Chain Lakes Reservoir is similarly operated to augment late summer and winter flow on Willow Creek.

An offstream reservoir is created by building a dam across a natural coulee to block drainage. Water is then diverted from a river and brought to the reservoir by gravity or by pumping. All the offstream reservoirs in Alberta are in the southern half of the province and are primarily used to store water for irrigation. These reservoirs are filled in spring when flow in the rivers is high, then water is withdrawn to irrigate crops in the summer. The reservoirs are partially filled again in the fall if flow in the rivers is adequate. Examples of offstream reservoirs in Alberta include Crawling Valley, Milk River Ridge, Little Bow Lake reservoirs, and Chestermere, McGregor and Payne lakes. Travers Reservoir is an "onstream reservoir" in the sense that it fills the valley of the Little Bow River, but it is also an "offstream reservoir" because 97% of its water is diverted to it from the Bow River.

P.A. Mitchell and J.M. Crosby