A watershed (or basin) is the area of land that catches snow and rain and drains it to a larger body of water, such as a marsh, lake, stream or river. Topography defines the entire watershed, as it shapes the course and speed of water moving through the area.
Watersheds can range in size from a few hectares to thousands of square kilometres (the Alberta part of the Battle watershed is 25,000 km2). All watersheds flow from headwaters (the headwaters of the Battle watershed come from Battle Lake) to outlets (the Battle River empties into the North Saskatchewan River), eventually ending in the ocean (Hudson’s Bay).
Watersheds fulfill three primary functions: to capture water, filter and store it in the soil then release it into a water body.
Watersheds sit on top of groundwater. Surface water and groundwater (see Parts of a Watershed) are connected in a watershed. Surface water seeps through the soil, moving downward to fill the cracks and spaces between rocks and soil particles, thereby becoming groundwater. Groundwater is stored in the soil and rock. Many people believe that groundwater comes from fast flowing underground rivers and lakes. This is not true.
Groundwater is always naturally in motion. Recharge areas are places where surface water soaks (infiltrates) into the soil to become groundwater. Discharge areas are places where groundwater seeps or flows into surface water (e.g. springs). The Battle River is fed by many springs along its length.
Run-off collects pollutants as it flows across land in a watershed. Polluted run-off flows into rivers, creeks, wetlands and lakes. It also seeps through the soil into groundwater.
Wetlands and riparian vegetation (plants growing alongside rivers, lakes, etc.) are like giant sponges. They store water, filter out pollutants and diseases, and slowly release the water into groundwater and/or rivers, creeks and lakes.
Watersheds are healthy when:
Humans affect the health of watersheds in their everyday lives, when they remove trees and plants, damage riparian vegetation, fill wetlands, pollute land or water, build homes or cultivate floodplains, create impervious surfaces (paved roads/parking lots), use large amounts of water, or change the flow of water with dams, weirs and culverts. See You and Your Watershed for more information.
For more information
Getting to Know Your Local Watershed a Government of Alberta Publication