Overview

HEC-HMS (Hydrologic Modeling System) is a software application designed to simulate the complete hydrologic processes of watershed systems, primarily for flood forecasting, water availability studies, urban drainage, flow forecasting, and reservoir spillway design. HEC-HMS is widely used by engineers, hydrologists, and water resource professionals across the U.S. and internationally. It’s designed to be flexible, scalable, and compatible with other HEC tools.

Key Capabilities:

  • Rainfall-runoff modeling: Simulates how precipitation translates into runoff within a watershed.
  • Hydrologic routing: Models the movement of water through rivers, channels, and reservoirs.
  • Loss modeling: Includes methods for estimating infiltration and surface runoff.
  • Baseflow and snowmelt modeling: Accounts for subsurface contributions and snow processes.
  • Forecasting and real-time operations: Supports real-time flow forecasting when integrated with systems like CWMS.

Accomplishments

Host CWMS NIP Workshop on HEC-HMS Calibration

The team hosted a virtual workshop in April 2025, with about 30 participants in attendance. The workshop focused on helping attendees improve the efficiency of HEC-HMS model calibration for real-time operations, with instructors providing hands-on guidance and best practices.

Participate in CWMS NIP Monthly Working Sessions

The MMC hosts monthly working sessions on Microsoft Teams, providing HEC-HMS modelers with access to expert support. The team participated in these sessions during FY25, as they have been highly valuable to users. These meetings are an effective platform for delivering field support, answering questions, and demonstrating key software features.

Develop New Tutorials and Host Webinars

New tutorials and guides were developed on managing data, models, and utilizing AI in calibration. Additionally, a basic calibration guide was developed from some sections of the UM and translated into a guide. 

Test HEC-HMS in CWMS 3.5

HEC-HMS 4.12 was extensively tested in CWMS 3.5 as well as HEC-HMS 4.13. Testing is continuing with HEC-HMS alpha builds to help get any potential issues taken care of before the software is released. 

Provide Field Support

Regular field support was provided with a focus on HEC-HMS related issues throughout the FY. 

Find and Fix Bugs

Plenty of bugs were discovered and resolved throughout the FY to help ensure the best product to the users as we could develop. 

Update HEC-HMS Plugin

This is a behind the scene update that users should not see. The objective of this task was to update some of the code to newer standards and update to more modern processes where applicable. 

Automated Optimization Feature

The Optimization Analysis framework has undergone significant refactoring to support multiple objective locations and time-windows. A key addition is the new "Sequential Search" objective type, which optimizes parameters progressively from upstream to downstream locations while locking optimized parameters in place along the way. The framework now includes scale factor capabilities for both baseflow parameters (Linear Reservoir and Recession Constant) and snow parameters (Temperature Index). To enhance usability, new tools have been developed including a builder and guided wizard that help water managers seamlessly create and parameterize Optimization Analyses linked to Forecast Alternatives. These optimized parameters can then be automatically pushed to Forecast Alternative override parameter tables through a newly implemented framework. Comprehensive documentation has been created to support these enhancements, including a tutorial, user guide, and demo video that showcase forecast optimization workflows. Currently under development are two additional features: an alternative workflow that enables snow parameters to be optimized independently from other basin parameters, and a data variant enhancement that will allow computes to initialize using states defined in a Forecast Alternative. This will be included in HEC-HMS version 4.14.

Implement Flag to Suppress Version Update Window

Suppressing the version update window was completed to help with automated testing within the CWMS application. The purpose of the flag was to make it to where a user did not have to approve an update and HEC-HMS would update automatically. This was included in HEC-HMS version 4.13

Updates to Check Box for Blending Feature

A checkbox was added to the blending editor. This allows for the modelers to toggle on and off blending rather than having to change the "Blending Method" to none. The blending setting will now persist when the modeler wants to enable it back on later in the process. This will be included in HEC-HMS version 4.14.

Dynamically Adjust Project DSS File to Current Forecast DSS File

Traditionally, HEC-HMS would maintain the project dss file and this would cause some portions of the HEC-HMS compute to be directed to the project dss file instead of forecast.dss. With this update, the forecast.dss becomes the project dss file, within an HEC-RTS forecast simulation, and everything that is computed by HEC-HMS will now be saved in the forecast.dss file. This will be included in HEC-HMS version 4.14.

Update Action Buttons in CAVI

The Forecast Configuration and Zone Configuration buttons were removed from action buttons in the CAVI. These two items should not be modified within the forecast and should be altered in the base HEC-HMS model if they are going to be modified. The Calibration Summary Table button was moved from the action tab to the reports tab. This will be included in HEC-HMS version 4.14.

Design for Capability to Keep Old Results in Plots

The initial design was completed for keeping a prior model results in a plot to see how the model modification impact the results. The work to implement this new capability will be spread out across FY26 and FY27.  

Develop Specified Release Method for Evaporation

This was a feature to allow for evaporation to be calculated in a reservoir element using the specified release method. The feature to have evaporation in the specified release method has been implemented and will be in HEC-HMS version 4.14.

Add Observed Inflow, Outflow, and Storage for Reservoir Elements

Observed inflow, outflow, and storage for reservoirs have been added as an option for reservoir elements in HEC-HMS. This will be included in HEC-HMS version 4.14.

Improve Tool Tips within Snow Components Editor

Detailed tool tips containing a description of the parameter, available methods, and typical values were added to all available Snow methods.  These tool tips can be accessed by hovering your cursor over the parameter of interest within each Snow method Component Editor.This was included in HEC-HMS version 4.13.

Enable the Use of Combined Parameter Editor within Standalone HEC-HMS

The Combined Parameter Editor has been accessible through the CAVI for some time but has never natively been in HEC-HMS until now. Now we can get to the combined parameter editor when working on a forecast in standalone HEC-HMS. This will be included in HEC-HMS version 4.14.