HEC-ResSim

Overview

HEC-ResSim (Reservoir System Simulation) is a software application designed to model and simulate the operations of reservoirs and reservoir systems to support water resources planning, management, and real-time decision-making. HEC-ResSim provides water managers and engineers with a powerful tool to evaluate how reservoirs should be operated under varying hydrologic conditions, helping to meet competing objectives and regulatory requirements efficiently.

Key Features:

• Simulates reservoir operations based on user-defined operating rules, policies, and objectives.
• Models both individual reservoirs and multi-reservoir systems.
• Supports rule-based and goal-based operations for flood control, water supply, hydropower, environmental flows, and recreation.

Accomplishments

Incremental Improvements to Code Management

• Migration to HEC Monolith 6
• Migration to Java 21
• Extraction of ResSim specific classes from shared code to the ResSim codebase.
• Updated ResSim code standards

HEC-ResSim 4.0 Testing 

• New automated compute testing setup in Bitbucket for running tests with each build. The new automated testing tool allows developer to quickly find issues they might have introduced before the code is integrated. 
• Compute tests were uploaded to the automated testing system.
• Some ResSim tests were added to the CWMS testing suite to verify integration of ResSim with HEC-RTS.

Evaluate, Prioritize, and Fix Bugs

• A portion of the >500 issues addressed in FY25 were in support of and supported by CWMS programs. 
• 20 critical ResSim bugs that impacted use with HEC-RTS were fixed.

Provide Field Support

The team provided support to assist field staff in using HEC-ResSim within CWMS. Approximately 190 hours were spent by the team assisting users in FY25.

Update Documentation

• New HEC-ResSim 3.5.1 Patch Release Notes
• New HEC-ResSim 4.0 User's Manual (updated from 3.5 UM)
• Documentation describing the new ResSim Variants functionality (new feature in Version 4.0)

Develop New Tutorials

• How to use global variables in a scripted rule
• How to make a stream alignment from NHD shapefiles
• OSI (Operation Support Interface) Tutorial
• How to Remove Variants from ResSim 3.5

Participate in CWMS NIP Monthly Working Sessions

The MMC hosts monthly working sessions on Microsoft Teams, providing HEC-ResSim 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.  

OSI Enhancements

A contract was awarded at the end of FY25 for three improvements to the ResSim OSI, work is on schedule to finish by February 2026 and be included in CWMS 3.6.