WMS:MODRAT Edit Parameters

Attributes or parameters for all MODRAT hydrograph stations are defined and/or edited using the Edit MODRAT Parameters dialog, shown below. This dialog is accessed by selecting the Edit MODRAT Parameters command from the MODRAT menu or by double-clicking on a basin, reach, or relief drain when MODRAT is the active model in WMS.

If a subarea, reach, or relief drain is selected before issuing the Edit MODRAT Parameters command, then the data for that object is loaded for editing. When a hydrograph station is selected (subarea/reach/relief drain), only the items which correspond to the selected hydrograph station are active, all others are inactive. For example, when a subarea is selected, all items under the Basin Data heading are active and all items under the Reach Data heading are inactive.

Once the Edit MODRAT Parameters dialog appears, it will remain open until the user selects the Done button. This enables the user to switch between basins, reaches, or relief drains quickly and define the necessary parameters without closing and opening the dialog for each hydrograph unit.

Location

The number entered in the Location field of the MODRAT Parameters dialog indicates the place in computational order the subarea or reach occupies. Computations in MODRAT begin at location 1 and continue sequentially. The location assignment is generally done automatically in WMS; for more information on numbering your watershed model, see the MODRAT Numbering the Tree section.

Lateral

The letter entered in the Lateral field of the MODRAT Parameters dialog indicates the line to which the subarea or reach is connected. The main line in any MODRAT model is line A; laterals may be labeled B through Z. Reaches with two letters indicate a confluence point of two or more reaches. The lateral assignment is generally done automatically in WMS; for more information on lettering your watershed model, see the MODRAT Numbering the Tree section.

Area

Enter the tributary area, in acres, of the subarea. If the WMS graphical modeling tools have been used to define the watershed from digital data, the area of each subarea will be automatically computed and will appear in this text field. If not, you must manually enter the area of each subarea.

Soil Type

Determine the soil type most representative of each subarea, between 2-172 for normal soil conditions and 202-372 for burned soil conditions. Soil type maps from LACDPW are used to find which soil is predominant in the subarea. This procedure has been automated in WMS; a digital soil map may be imported into WMS and overlaid on the watershed to be modeled. WMS will then calculate which soil covers the majority of the area of a subarea. This function is part of “mapping MODRAT attributes”; a full description can be found in the Map MODRAT Attributes section. If the watershed being modeled has not been graphically defined in WMS, enter the appropriate soil number based on visual inspection.

Impervious Area

Define the percent of the subarea that is impervious to infiltration. The percent impervious generally depends on the land use in the basin; as with soil type, land use maps have been developed to allow definition of this parameter through graphical analysis. WMS can determine the percent impervious by mapping MODRAT attributes, or the user may enter this number independently.

Rainfall Depth

To compute the rainfall depth on the sub-basins of your MODRAT model, you must read in a rainfall depth data layer. The isohyetal maps for LA County have been digitized and stored in ARC/INFO® Grid format by the LACDPW; these files can be found in the /MODRAT/Rain/ folder installed with WMS. Import this data by choosing Open from the File menu, then choose Rainfall Depth Grid (*.*) as the file type.

Alternatively, if you have other rainfall data in vector format (ArcView® Shapefiles, DXF, etc.) you can import these into WMS. Make sure that you create a Rainfall Coverage (see the Coverages dialog) and map the appropriate database fields when importing this data.

Once the rainfall depth data is present in WMS, you can compute and assign depths using the Compute GIS Attributes command from the Calculators menu.

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Related Topics

• Basin Data
• Reach Data
• Mapping Parameters from GIS Data Files
• Job Control Parameters
• Location
• Lateral
• Renumbering the Tree
• I/O