In this section, you will examine the setup and parameterization of the Arroyo Seco model. The model parameters have been calibrated to the first flood event post-fire, which occurred in January 2010.

Meteorologic Model

The components of the Meteorologic Model have been entered for you. This section describes the data sources used to develop the Meteorologic Model

  1. Expand the Meteorologic Model folder in the Watershed Explorer and select the LAPW_Interp_PRISM_Bias meteorologic model. Hourly precipitation records from gages were provided by the Los Angeles County Department of Public Works (LAPW). The Interpolated Meteorology method was used to spatially distribute the gage data across the modeling domain. In addition, the Parameter-elevation Regressions on Independent Slopes Model (PRISM) 30-year precipitation normals grid was used to bias correct the gaged precipitation. Both datasets were included with the project start files in the ...Arroyo_Seco_Tutorial_Start\Arroyo_Seco\data directory.
  2. Expand the LAPW_Interp_PRISM_Bias meteorologic model. Select the Interpolated Precipitation node. The Interpolated Precipitation tab should appear as in the image below. The Radius of Influence for the precipitation gages was determined using geospatial software.
    Meteorologic Model Interpolated Precipitation and Bias Grid Adjustment
  3. Monthly evaporation data was obtained from the Los Angeles County Department of Public Works Hydrologic Reports.


    Evapotranspiration (ET) constitutes a key component of the annual water balance in arid and semi-arid regions. Therefore, it is important to model ET in continuous simulations.

     Evaporation data from 2001-2018 was used to develop monthly average rates of evapotranspiration. Expand the ArroyoSeco_S10 subbasin node and select the Monthly Average node. The Monthly Average tab should appear as in the image below.
    Meteorologic Model Monthly Average Evaporation

  4. Collapse the Meteorologic Model folder.

Basin Model

  1. Expand the Basin Model folder and select the Jan_2010 basin model node.
  2. The Subbasin tab describes the model structure and selected model methods.  Make sure your selected methods are the same as the figure below. 
    January 2010 Basin Model Component Editor
  3. Navigate to the LossBaseflow, and Transform tabs and examine the model parameters.
  4. Variable Clark Unit Hydrograph Transform parameters were developed by HEC for the California Department of Water Resources Division of Dam Safety.  A workshop illustrating how these parameters were developed using the 2D Diffusion Wave Transform method can be found here. The Percentage Curves used to parameterize the Variable Clark unit hydrograph method can be viewed within the Paired Data Percentage Curves node. Additional information on the Variable Clark Unit Hydrograph method can be found in the HEC-HMS User's Manual and in the HEC-HMS Tutorial and Guides.

Initial Post-fire Event Calibration

The model was calibrated to the first post-fire flood event to determine the infiltration rate of the burnt soil. The Arroyo Seco watershed experienced a flood event in January 2010, approximately 3 months after containment of the Station Fire. The calibrated model had a Constant Loss Rate of 0.15 in/hr. This loss rate will be used as an estimate of the Dynamic Surface Initial Rate in the following steps. Results from the calibrated model are shown below.

January 2010 Results Graph

January 2010 Summary Results

Continue to Parameterize the Dynamic Surface Method and Compute a Simulation.