Specified Hyetograph

The program includes a rich variety of methods for processing raw precipitation data into a hyetograph for each subbasin. However, there are so many methods for processing precipitation data that it is not feasible to include all of them within the program. This method allows you to process your own data and provide a hyetograph for the program to use. You may also choose to subdivide a watershed into many subbasins so that it becomes reasonable to use only one precipitation gage for each subbasin. In either case, the program makes no assumptions about the source of the precipitation data, it only applies the hyetograph to each subbasin as specified by the user. The hyetograph is entered in the program as if it were gage data.

While all of the major processing of the raw data must be performed external to the program, some "convenience" processing is done. The hyetograph entered by the user will be at some interval, for example, 15 minutes. However, you may wish to use control specifications with a time step different from the original data. Instead of re-entering the data manually, the program will automatically interpolate the data to the requested time step. While the data may be entered as incremental or cumulative, it will be converted to cumulative before interpolation is performed. The interpolation process does not affect the original data, it is performed "on-the-fly" during a compute so that the data agrees with the time step.

The hyetograph entered by the user inherently includes both volume and timing information. In most cases the data should be used exactly as entered, with the possibility of interpolation described above. In some cases it is convenient to prepare a hyetograph that should be treated as a pattern. In this case, the volume implicit in the hyetograph is not as important and the timing pattern it represents. You may optionally enter a total storm depth when selecting a hyetograph for each subbasin. This can be useful when examining the impact of the same storm occurring with a different precipitation depth.