Welcome to Version 4.0 of the U.S. Army Corps of Engineers Reservoir System Simulation (HEC-ResSim) software, developed by the Hydrologic Engineering Center (HEC) and the U.S. Army Engineer Research and Development Center’s Environmental Laboratory (ERDC-EL) in collaboration with Resource Management Associates (RMA), Portland State University (PSU), and the USACE Northwest Division (NWD). This user manual describes the new water quality modeling capabilities of HEC-ResSim and serves as a supplement to the HEC-ResSim User’s Manual. For general information on the HEC-ResSim software, users should refer to the HEC-ResSim Version 4.0 User's Manual.
The HEC-ResSim water quality Graphical User Interface (GUI) allows users to: (1) define meteorological stations and their data sets, (2) select modeled water quality constituents, (3) define water quality parameter methods and values, (4) define the water quality geometry (e.g., vertical cells, longitudinal cells), (5) define initial and boundary conditions, (6) define observed water quality stations and their data sets, and (7) visualize and analyze model outputs through plots and reports.
In the water quality domain of the ResSim network, reservoir elements are simulated using a one-dimensional (1D) vertical transport scheme, where each reservoir is discretized into a set of well-mixed vertical layers. Conversely, the connecting river reach elements are simulated using a 1D longitudinal (downstream) transport scheme, with each hydrologic reach represented as a series of well-mixed segments.
The 1D water quality model calculates the transport and transformation of water quality constituents. The physical transport solver is based on a 1D advection-diffusion equation, with additional terms to account for boundary inflow and kinetics. Boundary inflow refers to additional water entering the water body, while kinetics represent the biochemical reactions and sediment-water interactions affecting water quality constituents. These kinetics are computed using water quality libraries (modules), including: (1) the Water Temperature Simulation Module (WTSM), (2) the General Constituent Simulation Module (GCSM), and (3) the Nutrient Simulation Module I (NSMI).
Water quality computations are fully integrated within the HEC-ResSim software. The GUI also allows users to create rules that incorporate water quality objectives and/or constraints alongside other operational objectives in the HEC-ResSim model. This capability enables the inclusion of water quality objectives in reservoir release decisions. To perform a water quality simulation in HEC-ResSim, a completed ResSim flow model and a corresponding water quality input data set are required.