The ModClark transform method requires a grid region, the grid region is a reference to a grid cell file. The file defines cells for each subbasin. Parameters for each cell are also included in the grid-cell file. This appendix describes the grid-cell file format. The file can be produced using available geographic information system (GIS) tools.

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.


Parameter Order: Xcoord YCoord TravelLength Area
End:
Subbasin: 85
Grid Cell:   633   359   88.38   3.76
Grid Cell:   634   359   84.51   0.18
Grid Cell:   633   358   85.55   16.13
Grid Cell:   632   358   82.55   12.76
Grid Cell:   625   348   13.75   12.07
Grid Cell:   626   348   17.12   0.09
Grid Cell:   622   347   21.19   3.26
Grid Cell:   623   347   15.56   9.96
End:
Subbasin: 86
Grid Cell:   637   361   59.13   6.79
Grid Cell:   638   361   59.04   6.95
Grid Cell:   636   361   56.68   1.17
Grid Cell:   636   360   55.08   16.38
Grid Cell:   636   347   67.96   2.45
Grid Cell:   637   347   71.72   7.41
Grid Cell:   638   347   72.57   8.78
Grid Cell:   639   347   73.32   0.04
End:
Sample grid cell file.