Overview

This workshop illustrates four methods for estimating debris yield using HEC-HMS model.  This workshop focuses on using an existing HEC-HMS model with a debris basin and calibrating erosion parameters to estimate debris yield. The condition of the existing HEC-HMS model might not always be clear.  It is important to review the model and understand any assumptions that might have been made when the model was developed.  It is also important to look over the calibration results and see whether the computed simulation does a good job at replicating measured accumulated debris yield volume based on the debris basin clean-out records, and assess whether additional adjustments or calibrations need to occur.   In this workshop, you will summarize the model parameters in the existing HEC-HMS model and choose appropriate input parameters for the debris yield simulation.  

Data

Download the initial model files here - Debris Yield Workshop with DB - Existing Model_Initial.7z

Review the Model

  1. An HEC-HMS model named Mountain_Fire_2002 was prepared following steps outlined in the HEC-HMS Tutorials and Guides listed below.  
    1. Creating a Simple Model
    2. Creating a Georeferenced Model using HEC-HMS GIS Tools
    3. GIS Tutorials and Guides
  2. Launch HEC-HMS (version 4.10 or later) and open the project by selecting File | Open | Browse.  Navigate to the project and select the HEC-HMS project Brand_Debris_Basin.hms. Select the Basin Models folder to expand the Watershed Explorer and see all basin models in this project.  You should notice a separate basin model for each debris yield method (LAEQ1, MSDPM, USGS_EA, and USGS_LT).  The first Basin Model, named Brand_Canyon_LAEQ1, was prepared as a case study to define the initial set of model parameters and the final set of model parameters to be used in the debris yield simulation with the debris basin. The last three basin models were prepared as additional tasks for users who have more interested in the other three debris yield methods.
  3. Select the Brand_Canyon_LAEQ1 Basin Model. 
  4. Select the Brand_Canyon subbasin element.
  5. On the Subbasin tab, change the Erosion Method to LA Debris Method EQ1.

  6. Calculate Relief Ratio by selecting Parameters | Characteristics | Subbasin.
    1. Convert Relief Ratio from dimensionless unit to M/KM by multiplying 1000
  7. Select the Erosion Tab.
  8. Populate the Erosion parameters based on the given field data shown below.  Parameter are described in the User's manual.
    1. A-T Factor: 1.0 (Set "1" as a default value because Brand debris basin is located in Southern California areas)
    2. Relief Ratio (M/KM): 216.19 (from Subbasin Characteristics)
    3. Fire Factor Method: Pak & Lee Fire Factor (by the user's option)
    4. Date (DDMMMYYYY): 02Sep2002 (from Fire record)
    5. Percent: 90 (from Fire Map)
    6. Flow Rate Thresholds (M3/S): 0.001 (Calibration Factor: This value will be calibrated later with the debris yield measured data)
    7. Exponent: 1 (Default Value)
    8. Gradation Curve: Debris Flow Mixture (from soil samples at the debris basin location)
  9. Select the Brand_DB reservoir element. This reservoir element was setup using the following field data. 
    1. Method: Outflow Structure
    2. Storage Method: Elevation-Storage-Area
    3. Elev-Stor Function: Brand_DB (this E-S curve was estimated based on 10-DEM and 100% & 25% capacity contour lines) 
    4. Elev-Area Function: Brand_DB (this E-A curve was estimated based on 10-DEM and 100% & 25% capacity contour lines) 
    5. Initial Elevation (M): 262 (assumption)
    6. Main Tailwater: Assume None
    7. Time Step Method: Automatic Adaption
    8. Spillways: 1
  10. On the Reservoir tab, change the Sediment Method to Chen Sediment Trap.

  11. Select the Sediment Tab.
    1. Select Yes for the Reservoir Capacity Method
    2. Select Elongated Taper (User's Manual) for the Deposition Shape
  12. Run Brand_DB_LA_EQ1 by selecting Run: Beand_DB_LA_EQ1 then click the raindrop icon .
  13. Compare the initial results with measured data.
    1. Go to your project folder
    2. Open the output DSS file Brand_DB_LA_EQ1.dss for LA EQ1 method
    3. Double-Click three accumulated reservoir bottom sediment results for Silt, Sand, and Gravel as shown below
    4. Click on Tools | Math Functions...
    5. Click on the Statistics tab then read Maximum Value as a accumulated server bottom sediment amount from the reservoir bottom for three grain sizes (silt, sand, and gravel) by changing Selected Data Set
    6.  Open the Measured Data.xlsx spreadsheet located in your project folder (Debris Yield Workshop with DB - Existing Model_Initial\previously_created_data) then select Initial Results tab. 
    7. Add your simulated debris amounts (TONNE) into this spreadsheet for each grain size (silt, sand, and gravel) to compare with measure volume of 81,358 M3


      Question 1: What is the difference between your calculated debris volume and measured debris volume?

      Difference: 20%

  14. Calibrate the Flow Rate Threshold value by minimizing the difference between your calculated debris volume and measure debris volume.

    1. In the Measured Data.xlsx spreadsheet, select the Calibration Results Tab to use for your calibration


      Question 2: What is your final value for the Flow Rate Threshold and percentage difference?

      Roughly, Flow Rate Threshold: 2.1 M3/S and Percentage Difference: -7%

  15. Compare the Elevation-Area curves between initial and final results for the Brand Debris Basin.
    1. Go to your project folder
    2. Open the output DSS file Brand_DB_LA_EQ1.dss for LA EQ1 method
    3. Double-Click two elevation-area curves results as shown below
    4. Plot the graphs by clicking the plot button
  16. Compare the Elevation-Storage curves between initial and final results for the Brand Debris Basin.
    1. Double-Click two elevation-storage curves results as shown below
    2. Plot the graphs by clicking the plot button
  17. If you are interested in other debris yield methods (MSDPM, USGS-EA, and USGS-LT), please follow the above steps for each method. With these additional tasks, you can see differences among four different methods as shown below and determine the best debris yield simulation result. 

Download the final model files here - Debris Yield Workshop with DB - Existing Model_Final.7z