Overview

This workshop illustrates four methods for developing debris yield application given an existing HEC-HMS model.  This workshop focuses on using an existing HEC-HMS model and making appropriate modifications for a debris yield simulation. The HEC-HMS model must be reviewed to understand assumptions made when the model was developed.  It is also important to look over the calibration results and assess whether the computed simulation does a good job at replicating measured accumulated debris yield volume (based on the debris basin clean-out records).  You may need to make additional adjustments and/or calibrations based on your assessment.   In this workshop, you will summarize the model parameters in the existing HEC-HMS model and choose appropriate input parameters for the Brand Debris Basin watershed debris yield simulation.  

Data

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

Review the Model

  1. A initial HEC-HMS model with Brand Canyon watershed delineated has been prepared for you.  Refer to the following HEC-HMS tutorials and guides listed below for more information on watershed delineation with HEC-HMS.  
    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 greater and open the project by selecting File | Open | Browse.  Navigate over to the project and select the HEC-HMS project named Brand_Debris_Basin.hms. Select the Basin Models folder to see all the 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, Brand_Canyon_LAEQ1, was prepared as a case study to define model parameters to be used in the debris yield simulation. 
  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 using the characteristics of subbasin element 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 initial subbasin parameters based on the given field data shown below.  Erosion parameters 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 Threshold (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. Run Brand_DB_LA_EQ1 by selecting Run: Beand_DB_LA_EQ1 then click the raindrop icon .
  10. 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 sediment load results for Silt, Sand, and Gravel as shown below
    4. Click on Tools | Math Functions...
    5. Click on Statistics Tab then read Accumulated Amount for three grain sizes (silt, sand, and gravel) by changing Selected Data Set
    6.  An excel spreadsheet named Measured Data.xlsx has been prepared for you which can be found in the project folder: Debris Yield Workshop wo DB - Existing Model_Initial\previously_created_data.   Select Initial Results Tab. 
    7. Add your accumulated debris amount (TONNE) to this spreadsheet for each grain size (silt, sand, and gravel) and compare with the measured volume of 81,358 M3


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

      Difference: 19%

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

    1. Keep the Measured Data.xlsx spreadsheet open and tab over to the Calibration Results to use for your calibration. 


      Question 1: What is your final value for the Flow Rate Threshold and percentage difference?

      Flow Rate Threshold: 1.7 M3/S and Percentage Difference: -6%

  12. 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 and determine the best debris yield simulation result. 

 

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