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Table Of Contents
Chapter 5 Working with Hydrology Commands
598
Viewing and Editing the Dimensionless
Hydrograph Values
A dimensionless unit hydrograph represents the runoff that occurs uniformly
across a watershed. It shows the relationship of q/qp (peak discharge) to t/tp
(time to peak), as shown in the following illustration:
Dimensionless unit hydrograph
The hydrograph uses one inch of rain as the rainfall amount, and assumes the
rainfall occurs at a uniform rate for a specified duration.
The Soil Conservation Society (now NRCS) developed an average dimensionless
hydrograph that the TR-20 Method is based on. Autodesk Civil Design provides
this dimensionless hydrograph file, scsdim.dim. This file is stored in the
c:\Program Files\Land Desktop R2\Data\hd folder.