Unit hydrograph analysis is used for watersheds greater than 1 square mile (640 acres) in Orange County, California. Losses are accounted for by calculating an effective precipitation. Runoff hydrographs are computed using a unit hydrograph, which is developed using an S-graph. You can use a small area hydrograph instead of a full blown unit hydrograph analysis for watersheds with a Tc < 25 min. WMS creates the input files required for HEC-1 to compute hydrographs for the Orange County unit hydrograph analysis. Much of the interface for the Orange County unit hydrograph analysis is similar to the HEC-1 interface within WMS. Some of the processes specific to Orange County are described below:
Effective precipitation - losses are included in the precipitation rather than defining a loss method
Unit hydrograph method - unit hydrographs are developed using Orange County S-graphs and lag time derived from the time of concentration computed in an Orange County rational method analysis
Stream/channel routing - a convex routing method is included in HEC-1
Flow-through detention - define using reservoirs or storage routing in HEC-1
Flow-by detention - define using diversions in HEC-1
Related Topics:
Editing HEC-1 Parameters
Job Control
Design Storms
Small Area Hydrographs
Using GIS Data
Running a HEC-1 Analysis
Saving a Simulation
Post Processing