Automatic Segmentation of HSPF Land Segments

The core functionality of WMS allows the automated delineation of watershed and sub-basins. Additional tools have been developed as part of the HSPF interface to allow automated breakdown of sub-basins to land-use based segments. These segments can then be modeled as PERLND or IMPLND segments in HSPF. Once the HSPF simulation has been initialized, these tools can be accessed.

The division of sub-basins to segments is performed as a GIS based combination of two data layers: a watershed data layer which contains basin boundary polygons, and a land use layer which contains land-use type polygons or gridded data. The two layers, or coverages, are compared to determine the land-use types which fall into each basin boundary. Then a segment is created for each land-use type in the basin. The area, type of segment (IMPLND or PERLND), and other parameters can be determined in this operation.

Automated segment generation in WMS is driven by the Compute GS Attributes dialog. Prior to invoking this dialog:

A watershed must be delineated and basin data computed.
A land use coverage or grid must be read into WMS.
HSPF data must be initialized in the HSPF Global Options dialog.

The dialog is opened by selecting the Compute GIS Attributes option from the Calculators menu in the Hydrologic Modeling module.

To generate the HSPF segments:

Select HSPF Segments from the Computation Type group.
Make sure the units of the watershed and land use data are set correctly by selecting the Units button and reviewing the settings.
Ensure that the land use coverage or grid is specified correctly.
Import a table that relates land use to HSPF parameters. This table is a simple text file that lists land-use ID, description, and pervious attribute as shown below.

11, “RESIDENTIAL”, “pervious”

12, “COMMERCIAL AND SERVICES”, “impervious”

13, “INDUSTRIAL”, “pervious”

16, “MXD URBAN OR BUILT-UP”, “impervious”

17, “OTHER URBAN OR BUILT-UP”, “pervious”

21, “CROPLAND AND PASTURE”, “pervious”

32, “SHRUB & BRUSH RANGELAND”, “pervious”

Click OK

This operation will create a segment for each unique land-use type in each basin, calculate the area, and assign the appropriate type (pervious or impervious) and name. These segments can then be modeled separately with HSPF.