What is a Watershed?
A watershed is the land drained by a stream or river system and/or associated wetlands and lakes.
A watershed can be as small as a few hectares (e.g., a wetland with-out external drainage) or as large as thousands of square kilometres (e.g., the Fraser and Columbia rivers).
Uplands often comprise more than 99% of the watershed’s area, with the floodplain and stream channel making up the rest. Uplands are associated with lowlands through the flow of water, either overland or through the soil. Vegetation slows the flow of water in the uplands so that it infiltrates the soil.
A riparian zone has vegetation that, due to the presence of water, is different from the vegetation of adjacent upland areas. Typically, riparian zones are adjacent to streams or waterbodies, but they also occur adjacent to springs and seeps. Vegetation slows the flow of water on the floodplain, thereby capturing sediment and building banks. A healthy riparian zone acts as a sponge, which slowly releases water to the stream or wetland over the course of the season, thereby maintaining water flow or water levels. A stream in a healthy condition should have ready access to its floodplain during high flow periods.
Good watershed management will result in a good connection between the uplands and the riparian area and between the stream, wetland, or lake and the floodplain or associated riparian area.
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Updated October 17, 2008