What is a watershed?
A watershed is the area of land where all of the water that is under it or drains off of it goes into the same place. John Wesley Powell, scientist geographer, put it best when he said that a watershed is:
“that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community.”
Watersheds come in all shapes and sizes. They cross county, state, and national boundaries. In the continental US, there are 2,110 watersheds.
Why modeling matters
Watershed modeling is one important tool utilized in a watershed study. It is most applicable when watershed modeling can be applied in either watershed sediment analysis, or watershed water quality analysis, or watershed habitat assessment.
Advanced with the computer technology and availability of standardized data sets, watershed modeling has more and more parts and components automated in comprehensive software systems. A typical example is the Geographic Information System (GIS). In watershed modeling, GIS is heavily used to manage, analyze and visualize the geospatial data sets, which are either the inputs or the outputs of the models.
Watershed modeling is a comprehensive system and method. It covers several specific models such as Terrain Modeling System to delineate watershed, drainage ways, stream network, cross section and floodplain, Hydrologic Modeling System (HEC-HMS) to simulate the run-off processes, Sediment Modeling System to identify sediment sources, calculate sediment load speed and volume, Water Quality Modeling System to predict the water quality in future, and so on. For different objectives or in different phases, these models/toolsets can be utilized independently or cooperatively.