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Utilizing Multiple Rain Gauges with Weighting in HEC-HMS for Watershed Simulation

This guide explores the use of multiple rainfall gauges in HEC-HMS to effectively model watershed responses. It outlines the steps for incorporating multiple gauge inputs, weighted by Theissen polygons, to simulate the impact of rainfall on the Ash Creek watershed during the May 1978 storm. Key learning outcomes include familiarity with the HEC-HMS graphical interface, the importance of project data storage, and various meteorological modeling techniques. By refining gauge data input and weighting contributions, users can enhance simulation accuracy for sub-basins.

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Utilizing Multiple Rain Gauges with Weighting in HEC-HMS for Watershed Simulation

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  1. Example 8 Multiple Rain Gages and Weighting in HEC-HMS

  2. Purpose • Illustrate the steps to use multiple rainfall gages on a watershed. • Multiple gage inputs to a sub-basin • Input weighted by gage weights, in the example determined by Theissen polygons.

  3. Learning Objectives • Reinforce use of HEC-HMS Graphical User Interface. • Reinforce the concepts of “Projects” as a data-storage paradigm. • Explore different meterological model concepts: • Initial loss and constant rate loss model • SCS Unit Hydrograph transformation model • User-specified hyetograph.

  4. Problem Statement • Simulate the response of the Ash Creek watershed at Highland Road for a 5-year for the May 1978 storm using the two recording rain gages as the input. • Treat the entire watershed as a single sub-basin. • Each gage contribution is proportional to their Theissen weights (determined elsewhere)

  5. Example 8 Multiple Rain Gages • Ash Creek Example 3 • Import basin model • Import meteorological model • Import time series model • Verify run, then save.

  6. Example 8 Multiple Rain Gages • Verify run, then save

  7. Example 8 Multiple Rain Gages • Examine the rainfall source file • Two gages • 14-W • 15-W • Theissen weights are unreported • 14-W = 0.12 • 15-W = 0.88 should work for this example

  8. Example 8 Multiple Rain Gages • Create two gages in Time Series manager • 14W • 15W

  9. Example 8 Multiple Rain Gages • Copy the date from the external file (Excel) into the respective gages. • Pay attention to non-uniform time, use the fill feature as needed Use chart to look for gaps in input

  10. Example 8 Multiple Rain Gages • Once gage data is entered, save. • Meteorological model is next, we need to change the model to allow multiple gages. Select “Gage Weights”

  11. Example 8 Multiple Rain Gages • Select which gages will be applied to Subbasin-1

  12. Example 8 Multiple Rain Gages • Select which gages will be applied to Subbasin-1

  13. Example 8 Multiple Rain Gages • Enter gage weights – in this case depth weights • Time weights are set to 1.0

  14. Example 8 Multiple Rain Gages • Run the model and examine output

  15. Example 8 Summary • Illustrate how to use multiple gage data and assign by weights each gages contribution to rainfall on a sub-basin. • Example can be extended to multiple sub-basins. • Gages need not be physically present on the watershed, but should be close by (same hemisphere?) • More exotic approaches are mentioned in Chapter 11, HEC-HMS user manual. • Weighting methods require external data preparation and weight determination

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