The ModClark transform method requires either the structured discretization or a file specified discretization that points to either a sqlite file or a *.mod file created by HEC-HMS. The file defines cells for each subbasin. Parameters for each cell are also included in the grid-cell file. This appendix describes the *.mod grid-cell file format. The file can be produced using available geographic information system (GIS) tools. The *.mod file is no longer recommended. Instead, it is recommended that you use the structured discretization option.
File Definition
The grid-cell file begins with the keyword "Parameter Order" followed by a colon and parameter keywords indicating the order for reading parameters from the file (see figure below). The keyword "End" must be on a line by itself after the "Parameter Order" line. Valid parameter keywords are shown in the table below. Parameter keywords are not case sensitive and are separated by spaces. If the parameter order is not defined, it is assumed to be: Xcoord Ycoord TravelLength Area. The coordinate system of Xcoord and Ycoord used in the file must match the coordinate system used in the gridded DSS records. Typically the coordinate system will be either hydrologic rainfall analysis project (HRAP) or standard hydrologic grid (SHG).
Parameter keyword definitions.
Keyword
Definition
Units
XCoord
x-coordinate of the southwest corner of the cell
integer value
YCoord
y-coordinate of the southwest corner of the cell
integer value
TravelLength
travel time index from the cell to the subbasin outlet
kilometers
Area
area of cell within the subbasin
square kilometers
The data for a subbasin begins with the keyword "Subbasin" followed by a colon and the subbasin identifier. One line beginning with the keyword "Grid Cell" follows for each cell in the subbasin. Data for the subbasin ends with the keyword "End". Keywords are not case sensitive and may contain spaces. Blank lines can be included and lines beginning with "#" are ignored as comments. The same grid-cell file can be referenced by more than one subbasin, allowing data for many subbasins to be stored in the same file. The identifier for a subbasin must be exactly the same in the grid-cell file as it is in the basin model.