CITY OF MANSFIELD STORM WATER MANAGEMENT
WATERSHEDS
What Is A Watershed?
A simple definition is that a watershed is the area of land that drains to a specified point. Many times, the specified point is a waterbody, like a lake, confluence, or bay. However, any point along a drainage path (stream, creek, or river) can be selected and the area draining to that point is the watershed for that point.
This image depicts a hypothetical watershed with flowpaths, and is used with permission from the Center for Watershed Protection.
There are other terms frequently used that relate to watersheds. A catchment is usually a much smaller area of land. Often detention ponds are said to drain a catchment. In the U.S., basins are very large collections of watersheds. The Joe Pool Lake watershed is a part of the West Fork of the Trinity River watershed, which is in turn a part of the Trinity River basin. The Trinity River basin drains an area from Cooke, Grayson and Montague Counties, in the north, all the way to Galveston Bay, near Liberty in the South.
Why Use Watersheds?
Watersheds are a useful way for water resource managers to make decisions. It is a logical manner for managing water resources. By using watershed boundaries, as opposed to jurisdictional boundaries, water resources managers are able to make more appropriate decisions about the quality and quantity of water in the area.
Focusing on water quality issues at a watershed scale provides a more holistic view of problems and solutions related to water quality and water supply. When problem solving on the watershed scale, it is necessary to identify and address all sources of pollution, as oppose to narrowing in on one problem at a time.
This reduces personnel demands, streamlines the management, and generally provides a faster turn around time on impacted watersheds. This is due in large part because multiple problems are identified and solutions implemented at the same time, instead of one problem being addressed and waiting to see the results before moving on to the next.
Management on a watershed scale also brings together multiple agencies with some water resource management tasks and responsibilities. This increases communication, and the probability that a solution for any particular problem can be identified. This also assists in the delegation of costs. No one agency becomes the sole financing body for solutions.
With the greater communication comes a more effective data-sharing network. Data collection activities can be streamlined and coordinated, and the costs can be shared across agencies to monitor more waterways more effectively than could have been achieved by any of the agencies alone.
Rural vs. Urban Watersheds
There are some properties that all watersheds share. When it rains in a watershed, the runoff from the storm will follow a route based on the topography, changes in elevation, of the land regardless of the land surface. However, an urban watershed will almost always produce more runoff at a faster rate than a rural watershed.
This is because urban watersheds generally have more roads, parking lots, rooftops, and other impervious surfaces that do not allow the rain to soak into the soil. The types of pollutants that can be found in the watersheds will be different as well. Regardless of the type of watershed, the easiest way to fight pollution is to prevent it from entering our lakes and streams.
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