Watershed management, watershed pollution, watershed restoration software

Watershed management, watershed pollution, and watershed restoration software

Flow Direction Vectors

Using the TOPAZ program created and distributed through the USDA, a flow direction is computed for each of the DEM cells. Flow paths can then be traced for any point on the DEM. Flow distance and slope along the path are easily determined from the DEM data.

Flow Accumulation

In addition to defining the flow direction from each DEM cell, the TOPAZ program determines the flow accumulation for each DEM cell. The flow accumulation is an integer number and represents the number of upstream DEM cells whose flow paths "pass through" the given DEM cell. In the figure below a display value has been set so that each DEM cell whose flow accumulation is greater than or equal to 200 is shown in blue. In reality it approximates where "channels" are on the DEM and is an essential part of establishing watershed boundaries.

Watershed Outlet

In order to delineate the watershed boundary, an outlet location needs to be identified. Typically you will want to create the outlet points in one of the "flow accumulation" cells (where there is a lot of contributing area upstream).

Basin Delineation

With the outlet point established, flow paths are traced from each DEM point (using the flow direction information computed by TOPAZ) to determine if it passes through the defined outlet point or not.

TINs

Triangulated Irregular Networks can also be used to delineate watersheds and set up hydrologic models. The first step in the process is to obtain elevation data. Elevations can come from DEM files, digitized data, or any other scattered xyz data source.




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