Cardinal Divide Viewpoint

Here are some examples and definitions of words commonly used to describe drainage basins or watersheds They come from the North American Lake Management Society (NALMS):

Definitions

Basin

A geographic area drained by a single major stream; consists of a drainage system comprised of streams and often natural or man-made lakes. Also referred to as Drainage Basin, Watershed, or Hydrographic Region.

Watershed

All lands enclosed by a continuous hydrologic drainage divide and lying upslope from a specified point on a stream. Also referred to as Water Basin or Drainage Basin

Drainage Area (of a stream at a specified location)

That area, measured in a horizontal plane, enclosed by a topographic (drainage) divide from which direct surface runoff from precipitation normally drains by gravity into the stream above the specified point.

Drainage Basin

Part of the surface of the earth that is occupied by a drainage system, which consists of a surface stream or water body together with all tributary surface streams and water bodies. The term is used synonymously with watershed, river basin, or catchment.

Catchment Area

(1)The intake area of an aquifer and all areas that contribute surface water to the intake area.

(2) The areas that are tributary to a lake, stream, sewer, or drain.

(3) A reservoir or basin developed for flood control or water management for livestock and/or wildlife. See also Drainage Area; Watershed.

(4) The land (including the streams, rivers, wetlands and lakes) from which water runs off to supply a particular location in a freshwater system. In North America, "watershed" is often used instead of "catchment area".

Catchment Area (Basin)

The area draining into a river, reservoir or other body of water.

Catchment Basin

The entire area from which drainage is received by a river or a lake; most generally used in reference to surface runoff.

River Basin

The area drained by a river and its tributaries.

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How a River Basin Works

Basins combine all aspects of the hydrologic cycle to create the lakes and rivers that we see. They combine rain and snow with evaporation and create the runoff that eventually collects in streams and lakes.

In addition to the many different terms for drainage basins, there are different sizes to consider. Typically, the larger the area of a drainage basin, the more water it generates. However, as basins integrate the weather, a large basin in a dry climate will produce less water than a large basin in a wet climate. Also as water runs downhill, steeper basins can generate more water than flatter basins. This is because as the water runs off of the landscape it moves faster and has less time to seep into the ground or evaporate.

Basins also have an impact on groundwater. Precipitation that is caught by the basin can seep into the ground and become groundwater. However, unlike surface water, groundwater is not confined by the basin and can extend well beyond the boundaries of the basin. The type of soil and numbers of lakes and rivers in a basin can be related to how much water will eventually end up in an aquifer as groundwater.

The amount of water a basin generates is called its yield. The yield of a basin can be expressed in one of two ways:

• The total volume of water it generates in a year - in m³ or dam³ (1000 m³);
• The total volume of water generated in a year divided by the area in km² - dam³/km² or mm.

The size of the basin is determined by the amount of surface area it covers and where the water will ultimately end up. In Alberta, we use these terms in order of magnitude for our basins:

Low Res	High Res

The area that ultimately drains to an ocean. These basins are defined by major continental divides. Alberta has three continental drainage basins. Depending on where you are in the province the water you see will eventually end up in one of three places - the Gulf of Mexico via the Missouri River system; Hudson Bay via the Saskatchewan/Nelson and Churchill River systems; or the Arctic Ocean via the Mackenzie River system.

A number of major river basins combine to form a continental drainage basin. In Alberta, the major river basins are defined by larger rivers and by other large areas of land contributing to streams that flow out of the province. The Water Act recognizes seven major basins for the purposes of administering the Act (as indicated in the first map, left). The second map (right) shows the most common river basins that are often referred to in Alberta.

A sub-basin is comprised of the areas that are drained via smaller rivers and tributaries. A number of sub-basins combine to form a major river basin, or larger sub-basin. Each sub-basin can be broken into smaller and smaller sub-basins. The number and size of sub-basins that an area is divided into is a function of the end use for the sub-basins. When looking at the Red Deer River Basin, sub-basins can be defined for the major tributaries as seen in the Red Deer River Sub-basins map to the right. On a smaller scale, each of the sub-basins can be further broken down into smaller sets of sub-basins like the ones shown in the Little Red Deer River sub-basins map.

A drainage area is the area draining to a specific point on the landscape. Examples of drainage areas would be the areas draining to a culverts, dugouts or drainage ditches.