There are occasional circumstances where an HEC-HMS modeler may prefer to run a non-gridded hydrologic model using basin average hyetographs instead of gridded precipitation data. Fortunately, HEC-MetVue makes it very simple to compute and save basin average hyetographs as well. This task will walk the user through this process.

Save Hyetographs to DSS.

Return to HEC-MetVue and generate Basin Average Hyetographs from the "Radar – Trimmed – Translated" Map Window.

  • Click on the "Radar – Trimmed – Translated" Map Window.
  • Right-Click on the BaldEagle.shp and select "Make Basin Average Map" if it is not already selected.

Notice how the basin-average event totals are displayed within the Bald Eagle subbasin.

  • Click on the "Save Time Series" Tool
  • Check the box to "Write to DSS"
  • Browse to and select the DSS input file for the HMS model:

...\HEC-MetVue_Overview_Workshop\HEC-MetVue_Overview_Solution\HEC-HMS\BaldEagle\dss\BaldEagleHyetographs.dss

  • Specify the C Part as "PRECIP-INC"
  • Check the box to "Override F"
  • Specify the F-Part as "NEXRAD-TRANSLATED"
  • Press OK to save the basin average time series hyetographs to the BaldEagleHyetographs.dss file.

Run HEC-HMS (Specified Hyetographs).

Return to the HEC-HMS model and view the Specified Hyetographs Meteorologic Model.

  • Open the "Specified Hyetographs" Meteorologic Model details by clicking on "Specified Hyetographs" → Specified Hyetograph.

Notice that the "Specified Hyetographs" meteorologic model is utilizing Specified Hyetograph time series data instead of gridded precipitation. Looking towards the bottom of the explorer window we see that each subbasin is linked to its own basin average time series data.

  • From the HEC-HMS Compute Selection menu, select the "Run: Sep2018 – Translated – SH"

  • Select the Compute All Elements () icon to compute the Sep2018 - Translated - SH model which utilizes the specified hyetograph subbasin time series data.

View HEC-HMS Results (Specified Hyetograph).

Right-click on the Outlet element, "Lock Haven SNK" → View Results (Sep2018-Translated-SH) → Graph.

You can also select the "Summary Table" option to view quantitative metrics (peak flow, peak timing, volume, etc.) from the simulation.

It is important to note that the specified hyetographs were derived from the translated gridded precipitation. Therefore, results will vary depending on how each user uniquely translates and rotates the precipitation grids. The hydrographs above are simply one possible result.

Question: What is the Peak Flow of the Sep2018-Translated-SH event (using the specified hyetograph time series precipitation) at the Bald Eagle watershed outlet? 

The peak flow at Lock Haven SNK will vary for each user depending on the unique way they translate and rotate the gridded precipitation data from which the basin average time series data is derived. In the example above, the peak flow is about 20,000 cfs for the Sep2018-Translated-SH event when HEC-HMS was run with the specified hyetograph (basin average time series) data.

Question: How does the Sep2018-Translated-SH Peak Flow compare to the peak flow from your Sep2018-Translated event with the translated gridded precipitation data? 

The Sep2018-Translated-SH (basin average time series precipitation) peak flow should be slightly different than the Sep2018-Translated (gridded precipitation). Even though both events are based on the same gridded precipitation, they are applied differently within the HEC-HMS model.

The Sep2018-Translated event applied the precipitation grids spatially across the watershed so precipitation volumes varied from higher to lower areas of intensity.

The Sep2018-Translated-SH event applied a lumped, hourly basin-averaged precipitation value across each subbasin throughout the event so precipitation volumes were not varied throughout each subbasin. 

These differences may produce results of a similar overall magnitude, but will definitely vary slightly due to the spatially-variable (ie, gridded) versus lumped precipitation application methods.

One way to quantify the differences is by viewing the Summary Tables for each event:

Remember that values will vary by user depending on how the data was translated.

Comparing the Sep2018-Translated (with gridded precipitation, left) to Sep2018-Translated-SH (with specified hyetographs) simulations, we see that the peak discharge and volumes were slightly higher applying the gridded precipitation simulation (Sep2018-Translated) than with the specified hyetograph simulation (Sep2018-Translated-SH). 


Tasks

Part A – HEC-MetVue Orientation:

Part B – HEC-MetVue Data Input:

Part C – HEC-MetVue Precipitation Preprocessing for input into HEC-HMS :