What is a Watershed?

A watershed is defined as an area of land that drains to a common point.  A watershed is very much like a bowl; it has a ridge that defines its boundary and a valley that collects each drop of water that falls within its boundary.  Watersheds can vary in size, and smaller watersheds exist within larger watersheds.  Watersheds can be as small as the land draining to a neighborhood detention basin or as large as the entire Mississippi River Basin.  The Center for Watershed Protection classifies watersheds into five watershed management units.  These include catchment area, subwatershed, watershed, subbasin, and basin (see Table 1).  The primary planning authority and suggested management focus for each of the five watershed management units varies greatly depending on the size of the watershed.

Table 1: Watershed Management Units

(Thomas Schueler, Center for Watershed Protection. 1995)

Benefits of Watershed-based Planning

The planning area for watershed-based planning is determined by the boundaries of the watershed management unit itself.  Since watershed-based planning considers the entire drainage area, it is the most effective method to address water quality and quantity issues.  Watershed boundaries are formed by changes in topography and as a result rarely follow municipal boundaries.  Watershed-based planning creates a unique environment where multiple jurisdictions can work together to reduce duplication of effort and build on each other’s resources and information to solve water-related problems.  A multi-jurisdictional approach to addressing water quality issues often results in long-term cooperation and coordination among neighboring entities.  Watershed-based planning focuses on land use activities and how they directly affect the quality and quantity of water in streams, rivers, and lakes.