Last Modified: 2026-03-04 09:13:49.767

Software Version

HEC-HMS version 4.14-alpha was used to create this example. You can open the example project with HEC-HMS v4.14 or a newer version.

Project Files

Download the watershed polygon and stream line shapefiles here:

PMP_Workshop_Initial_2026.zip

Overview

This tutorial will guide you through the process of applying the HMR52 Meteorologic Model in HEC-HMS to manually maximize the Probable Maximum Precipitation (PMP) precipitation upstream of Sayers Dam. You will create a new HEC-HMS project by georeferencing an existing watershed polygon.  The goal of this task is to create a PMF basin model, set up the HMR52 Storm Meteorologic Model, run a simulation with the PMP event, and then use the Optimization Trial to maximize precipitation over a watershed.  

In this workshop, you will:

• Create a Basin Model and set the Basin Model coordinate system to Albers Equal Area
• Import GIS features (subbasins), and
• Define the loss, transform, and baseflow parameters
• Set up a HMR52 Storm Meteorologic Model
• Define a Control Specification
• Create and run the simulation
• Review results
• Create and compute Optimization Trial to maximize precipitation over the watershed

Create a New HEC-HMS Project and Define Coordinate System

1. Download and extract the initial project files.
2. Launch HEC-HMS.
3. From the File menu select New... to create a new project.  Call the project PMP_Workshop and make sure the Default Unit System is U.S. Customary. Click Create.
   
4. Start with the creation of a new Basin Model for the PMP analysis. Go to the Components menu and select Create Component | Basin Model... Name the model PMF_Sayers and click Create.
5. Before importing the shape file, the coordinate system for the basin model must be defined. To set the coordinate system, first activate the PMF_Sayers basin model in the Watershed Explorer by expanding the Basin Models folder and selecting the PMF_Sayers Basin Model. 
6. Select GIS | Coordinate System.
7. In the Coordinate System dialog, select the Browse button.
8. Navigate to where you extracted the zip file with the watershed polygon and stream line shapefile.
9. Select the Basin_Albers.shp file and click Select.
10. The coordinate system for PMF_Sayers should now be populated with Well Known Text (WKT) exhibiting an Albers Equal Area Projection as shown below. 
    
11. Click Set to establish the coordinate system for PMF_Sayers.

Question 1: Why would an Albers Equal Area projection be appropriate for a PMP analysis? Can you think of other projections that would be appropriate?

Import Subbasin

With the coordinate system set, the subbasin upstream of Sayers Dam can be imported as a GIS feature.

1. From the GIS menu, select Import Georeferenced Elements.
2. Make sure Element Type is set to Subbasins and click Next.
3. Browse for Basin_Albers.shp, select the file for import, and click Next.  
4. Select the field definition NAME to identify the attribute containing the name for the subbasin.
   
5.  Click Finish. You can view the newly imported GIS element Bald Eagle HW in the Desktop (upper right panel), as shown below.
   
6. The map panel has sparse detail and would benefit from additional map layers for visualization purposes. In the Watershed Explorer panel, select the PMF_Sayers Basin Model.
7. From the View menu, select Map Layers… | Add....
8. Select Reach_Albers.shp and click Select.
9. The current map layers should now include Reach_Albers, as shown below, and the Map Layers editor can be closed.
   

Define Hydrologic Parameters

Now that the Basin Model includes elements and map layers, it is time to parameterize the Bald Eagle HW subbasin element. 

1. In the Watershed Explorer, select the PMF_Sayers Basin Model node.
2. In the Component Editor, set the Unit System for the Basin Model to U.S. Customary.
3. Expand the PMF_Sayers basin model and select the Bald Eagle HW subbasin.
4. The Component Editor will activate as seen in the figure below.
    
5. On the Subbasin tab, set the Loss, Transform, and Baseblow methods to Initial and Constant, Clark Unit Hydrograph, and Recession, respectively.
6. Enter the Loss, Transform and, Baseflow parameters as shown in the following three figures below.  
   1. Select the Loss tab and specify the loss parameters, Initial Loss (IN) = 0.2 and Constant Rate (IN/HR) = 0.1.
       
   2. Select the Transform tab and specify the transform parameters, Time of Concentration (HR) = 9 and Storage Coefficient (HR) = 9.
      
       
   3. Select the Baseflow tab and specify baseflow parameters, Initial Discharge (CFS) = 1, Recession Constant = 0.7, and Ratio = 0.05.  
      

With the parameters set, it is now time to configure an HMR52 Storm Meteorologic Model.

Set Up HMR-52 Storm Meteorologic Model

HMR 51 and 52 Background Information

Hydrometeorological Report 51 (HMR51) contains the PMP index maps for the Eastern U.S. and Hydrometeorological Report 52 (HMR52) contains information about the application of the PMP depths to a watershed. Figures 18 – 47 in HMR51 contain depth-area-duration (DAD) PMP index values for the area east of the 105th meridian in the United States. The PMP documents have been digitized by the national weather service (NWS) (https://www.weather.gov/owp/hdsc_pmp). The table below contains most of the DAD PMP values for the Sayers Dam watershed. It is good practice to plot the DAD values in a plot similar to the one below to catch any mistakes when extracting the information for your watershed.

HMR51 Document
HMR52 Document

Question 2: What is the PMP depth for the 6-hour 5,000 square mile storm area using the HMR51 document?

Depth-area-duration PMP values for the Sayers Dam watershed

With the above DAD PMP values derived from HMR51, a Meteorologic Model for a PMP analysis can be created and populated in HEC-HMS.

1. Navigate to Components | Create Component | Meteorologic Model.... Name the model PMP and click Create.
2. The Meteorologic Model has been added to the project and can be found in the Watershed Explorer as shown below.
   
3. In the Watershed Explorer, select the PMP Met Model to activate the Component Editor.  
4. Under the Meteorology Model tab, change the Precipitation method to be HMR52 Storm.
5. When prompted to change methods, click Yes.
6. Set the Unit System to U.S. Customary.
7. The Meteorology Model should now be configured for HMR52 storm inputs as shown below.
   

The duration-precipitation functions must be added to populate the required HMR52 Storm information. These functions are defined as paired data.  

1. Go to the Components menu and select Paired Data Manager. 
2. Under Data Type, select Duration-Precipitation Functions from the dropdown menu. 
3. Click New... and name the first paired data set 10 sq mi, and click Create as shown below.  
   
4. Repeat this process for the remaining storm areas: 200 sq mi, 1000 sq mi, 5000 sq mi, 10000 sq mi, and 20000 sq mi.
    

Once the duration-precipitation functions are created, they can be populated with the data found in the above table.

1. In the Watershed Explorer navigate to Paired Data | Duration-Precipitation Functions and select 10 sq mi paired data entry to activate the Component Editor.
2. On the Paired Data tab, set the units to HR : IN. 
3. Select the Table tab and populate the table with the appropriate values as seen in the figure below.
   
4. The duration-precipitation data can be viewed graphically by selecting the Graph tab, as shown below.
   
5. Repeat the process for the remaining paired data entries: 200 sq mi, 1000 sq mi, 5000 sq mi, 10000 sq mi, and 20000 sq mi. 
   Note: it may help to copy and paste the left column containing the duration (hr) values into subsequent functions.

Now that the duration-precipitation functions are populated, the HMR52 Storm meteorologic model can be parameterized.

1. In the Watershed Explorer select Meteorologic Models | PMP | HMR52 Storm to activate the Component Editor.
2. On the HMR52 Storm tab, assign the X and Y coordinates for the storm center.  The X and Y coordinates can be estimated using GIS.  Use coordinates 4942618 and 6985660 as starting values.
3. Continue filling in the HMR52 Storm tab with the following information found in the HMR 52 document:
   1. Preferred Orientation (DEG) = 211
   2. Orientation (DEG) = 211
   3. Peak Intensity: Hours 36 to 42
   4. 1 to 6 Ratio = 0.305
   5. Area (MI2) = 350.  
   6. Link the Area to the appropriate Duration-Precipitation Functions as shown below.
      

Create a Control Specification

With the Basin Model and Meteorologic Model complete, the Control Specification can be created for the PMF simulation.

1. Go to the Components menu and select Create Component | Control Specifications. 
2. Name the new Control Specification PMF Event and click Create.
3. Navigate to the Watershed Explorer and select the Control Specifications | PMF Event node to activate the Component Editor. The Start Date, Start Time, End Date, End Time, and Time Interval should be specified as in the image below below.
   1. Set the Control Specification time window to be 01Jan1999 00:00 to 08Jan1999 00:00 and specify a Time Interval of 15 Minutes.
      

Create and Compute a Simulation Run

Lastly, create the Simulation Run. 

1. From the Compute menu, select Create Compute | Simulation Run.... Name the new Simulation run PMF Sayers and click Next. Select PMF_Sayers as the Basin Model and click Next. Select PMP as the Meteorologic Model and click Next. Select the Control Specification PMF Event and click Finish.
2. The simulation run is created and can be computed. From the Compute Toolbar select Run: PMF Sayers as shown below. Click the "exploding rain drop" compute button to run the simulation.
   

Review Results

Review results of peak flow, flow volume, and precipitation volume and record the results.

1. In the Watershed Explorer, click on the Results tab and expand the PMF Sayers node and then the Bald Eagle HW element node as seen in the figure below. Be sure to check out the Graph and Summary Table results and note the maximum peak flow computed for the Bald Eagle HW subbasin element. 
   
2. Now navigate to the Watershed Explorer pane under Meteorologic Models and select PMP | HMR52 Storm and experiment with different storm properties to maximize peak discharge at the Bald Eagle HW subbasin outlet. Try five additional scenarios (parameter combinations) and track your results. Focus on slight adjustments to the X and Y Coordinates, Orientation, and Area.

Map Pane Coordinates

Hover the mouse cursor over the Basin Map Pane to see the X and Y coordinates at the cursor's current location.

Question 3: What combination of Area and Orientation parameters produced the largest peak flow?

Create and Compute an Optimization Trial

Let's create and compute an Optimization Trial to find the HMR52 parameters that maximize precipitation in the watershed upstream of Sayers dam.

1. Create a new Optimization Trial by selecting Compute | Create Compute | Optimization Trial.... 
2. Call the new trial Maximum Precipitation. 
3. Use the PMF_Sayers Basin Model and PMP Meteorologic Model and click Finish on the last screen to create the trial.
4. On the Compute tab of the Watershed Explorer, expand the Optimization Trials node, and select the Maximum Precipitation trial. 
5. Set the Start Date and Time to 01Jan1999 00:00 and the End Date and Time to 08Jan1999 00:00. 
6. Set the Time Interval to 15 Minutes.
   
7. In the Component Editor, select the Objective tab. 
8. Select Maximization in the Goal drop-down menu. 
9. Leave the Statistic set to Total Precipitation and the Data Transformation set to No Transform.
10. Set the Time-Series option to Precipitation.
11. Leave the Data Transformation set to No Transform.
12. In the table, select Bald Eagle HW in the Location column. The Objective tab should appear as in the image below.
    
    
13. Save the project.
14. Navigate to the Search tab and change the Method to Differential Evolution. 
15. Set the Min Iterations to 40.
16. Leave the other fields.
    
17. In the Watershed Explorer, right-click on the Maximum Precipitation trial and select "Add Parameter". 
18. Repeat this 3 more times for a total of 4 parameters.
    
19. For the four parameters:
    1. Element: --Precipitation Parameters--; Parameter: HMR52 Storm - X Coordinate; accept default initial/min/max values
    2. Element: --Precipitation Parameters--; Parameter: HMR52 Storm - Y Coordinate; accept default initial/min/max values
    3. Element: --Precipitation Parameters--; Parameter: HMR52 Storm - Area; accept default initial value, set min to 10 sq mi and max to 2000 sq mi
    4. Element: --Precipitation Parameters--; Parameter: HMR52 Storm - Orientation; accept default initial/min/max values
       
       

Optimization Parameter Ranges

When using an Optimization Trial operationally (and not just for a workshop) it is important to set thoughtful, meaningful ranges for your parameters to make sure the search is bounded and goes quickly.  In this situation, we are lucky that the default ranges are good enough to start a trial.

1. In the upper ribbon, select Trial: Maximum Precipitation and click on the "exploding local minimum" icon to its right to run the trial.
   
2. Each evaluation should be very fast. Due to our settings, the model will run at minimum 1,200 evaluations (40 minimum iterations * 30 population size). The Optimization Trial should complete in 1-2 minutes.
3. In the Watershed Explorer, go to the Results tab and choose the Maximum Precipitation trial.

Question 4: Look at the Objective Function graph (3rd node), which tells you how the search for maximum precipitation progressed. Does it seem to converge on a value?

Question 5: Look at the parameter trace values for each of the four parameters.  Do they each seem to converge on a value?

Finally, look at the Optimized Parameters table.  Note the values for the four parameters that maximize total precipitation over the watershed.  Click on the Bald Eagle HW subbasin element under the trial, and click on the Summary Table.

Question 6: Did maximizing total precipitation also maximize peak discharge?  Is the peak discharge value higher than before?

Project Files

Download the final project files here:

PMP_Workshop_Final_2026.zip