In the last portion of the workshop, you will generate an inundation depth grid using HEC-RAS Mapper for the No Future Rain forecast run, compute the Future Rain forecast run (and generate a depth grid) and then analyze some of the results in HEC-RAS Mapper.

Generating a depth grid for the No Future Rain forecast run using HEC-RAS Mapper

In Task 1 of this workshop, you created the Depth (Max) saved map in HEC-RAS Mapper for our forecast run. You will now compute that map and view the depth grid.

  1. Open HEC-RAS Mapper. Notice that the Depth (Max) stored map layer we created earlier is not visible. The name will be italicized and it will have the red asterisk displayed, informing you the file does not exist.

  2. Right-click on the name of the layer and select Compute/Update Stored Map.
    HEC-RAS Mapper Window - Depth (Max) Not Created

  3.  Once the depth grid has been generated, zoom into different areas of the model and view the results.

Do you see any flooding occurring due to the "No Future Rain" event?

The inundation seem to be confined to the channel for the most part, so there does not appear to be any significant flooding from the "No Future Rain" event.

Computing the Future Rain forecast run and generating a depth grid 

As you probably noticed, there was no significant flooding from the event forecasted, mainly because we did not include the forecasted rainfall (QPF) in the model run. You will now compute the QPF forecast run (Future Rain) and analyze those results using HEC-RAS Mapper.

  1. Close HEC-RAS Mapper and HEC-RAS. Return to the Modeling module in the CAVI.

  2. Right-click on the Future Rain forecast run and select Compute.

  3. Once the forecast has finished computing, select the HEC-RAS model alternative from the forecast tree and from the Actions tab, choose RAS Mapper. Notice all of the various options available from the Actions tab for the HEC-RAS model.

  4. Once HEC-RAS Mapper opens (it may be hidden behind the CAVI), right-click on the Depth (Max) layer and create the saved map for the QPF forecast run. 
  5. HEC-RAS Mapper displays the results layers using the forecast key, and for the QPF forecast run it is M0H0N0R0. Notice that the results from our NO QPF run are no longer visible. HEC-RAS Mapper will only display the results from the most recent HEC-RAS model run. If you run multiple forecast runs simultaneously, the last run to compute will display within HEC-RAS Mapper. If you need to view results and generate output files for multiple forecast runs, you should compute each run individually.

    As shown below, maximum depth grid results from both CAVI forecasts are saved to individual folders in the HEC-RAS folder within the forecast directory. 
    Location of Max Depth Grids

What are the deepest inundation depths in the floodplain around the town of Lytton (near Geyserville and Healdsburg)? What may get flooded? 

Inundation depths are roughly 3 to 5 feet in the floodplain around Lytton. No structures appear to be within the limits of flooding, but some of the vineyards in the area may be flooded if the forecasted rainfall were to occur.

Prior Task(s):

Task 1: HEC-RAS Mapper Setup

Task 2: Running a Forecast with HEC-RAS

Current Task:

Task 3: Generating Inundation Depth Grids

Next Task(s):