Subbasin Characteristics
Geospatial Subbasin Characteristics can be computed within HEC-HMS. To compute subbasin characteristics, the Basin Model must have georeferenced subbasins and the GIS | Preprocess Sinks step, the GIS | Preprocess Drainage step, and the GIS | Identify Streams step should be computed beforehand. The Subbasin Characteristics view can be accessed from the Parameters | Characteristics menu. The first time the Subbasin Characteristics view is accessed, statistics are computed on-the-fly.
The subbasin characteristics computed include:
- Longest flowpath length
- Longest flowpath slope
- Centroidal flowpath length
- Centroidal flowpath slope
- 10-85 flowpath length
- 10-85 slope
- Basin slope
- Basin relief
- Relief ratio
- Elongation Ratio
- Drainage Density
It is important to note that the subbasin characteristics calculations are based on the original terrain data associated with the Basin Model. The calculations are NOT based on output that may exist from the GIS | Terrain Reconditioning step in HMS (build walls / burn streams). Full descriptions for each characteristic are provided below.
The image below illustrates the subbasin characteristics view for a Basin Model.
Subbasin characteristics can be recalculated using the Re-compute button in the lower-left corner of the dialog. The user has the option to override the computed characteristic values by manually editing the table values and clicking Apply to save the changes.
For more, see the Technical Reference Manual.
Reach Characteristics
In addition to subbasin characteristics, characteristics can also be computed for reach elements within HEC-HMS. As with subbasin characteristics, this functionality can be accessed from the Parameters | Characteristics menu. The Reach Characteristics calculators are capable of computing reach slope, reach sinuosity, and reach relief. The calculated results can be viewed in tabular format.
The image below illustrates the Reach Characteristics view for the MiddleColumbia_WY1997 Basin Model.
For more, see the Technical Reference Manual.