WMS:Weighted Average Precipitation

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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 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 the rain gages with the Create Feature Point tool. (Rain gages can also be added later on.)
  8. Right-click on a rain gage with the Select Feature Point/Node tool and select Attributes (or double-click on the gage). The Rain Gage Properties window will appear. 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.

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