Version 4.0 (October 2025) of the Reservoir System Simulation program (HEC-ResSim) is now available. This version supersedes Version 3.5 which was released to the general public in September 2024.
Several new features, as well as enhancements to existing features, have been added to the program since that time. The new features to look for are listed in the Version 4.0 Version 4.0 Release Notes.
Please refer to the HEC-ResSim User’s Manual for details regarding the new features, enhancements, and improvements.
We strongly recommend that
before you start using
HEC-ResSim 4.0 you
make backup copies of your existing watersheds (and consider using separate modeling locations (folders) for your v4.0 and v3.5 watersheds).