WMS:Weighted Average Precipitation

Once a watershed has been delineated, follow the steps below to use rain gage data to compute a basin average precipitation with HEC-1.

1. Switch to the "Drainage Module".
2. Select the "Select drainage unit or basin" tool and double click on the watershed which you would like to assign precipitation based on rain gages.
3. Select the "Precipitation" button.
4. Select the "Gage (PG)" option. Select "OK", then "Done".
5. Right click on the "Coverages" folder and select "New Coverage" to create a new coverage.
6. Change the "Coverage type" to "Rain Gage" and select "OK".
7. Create your rain gages with the "Create Feature Point" tool (you can also add rain gages later on)
8. Right click on a rain gage with the "Select Feature Point/Node" tool and select "Attributes" (you can also double click on the gage). The "Rain Gage Properties" window will appear. You can now do the following (NOTE: make sure the Show combo box in the upper right is set to All in order to view all gages):
   • Add additional gages with the "Add Gage" button
   • Edit the X, Y coordinates of each gage
   • Enter the amount of precipitation at each gage
   • Assign a temporal distribution to each gage by activating the "Temporal distribution" check box and selecting "Define".
9. Select "OK" when finished adding rain gages.
10. Switch to the "Hydrologic Modeling Module". Select the "Select Basin" button.
11. Double click on the basin.
12. Select the "Precipitation" button.
13. Select the "Gage (PG) option". Select "OK" and then "Done".
14. Select "HEC-1 | HEC-1 Rain Gages".
15. Select the rain gage coverage in the" Coverage:" combo box. Select "OK".
16. Select "DEM | Compute Basin Data" while in the "Drainage Module". Enter a "Gage weight computation cell size" and the select "OK".