New Modeling Capability In Hec-Hms

The Hydrologic Modeling System (HEC-HMS) is developed by the U.S. Army Corps of Engineers, Hydrologic Engineering Center. Many new capabilities have been released in recent software versions. This paper will document a few of the new modeling capabilities released recently and new software capabilities that provide improved control for results generation and visualization.

The Meteorologic Model underwent a major change starting in HEC-HMS version 4.9. An effort was made to streamline the meteorologic model and solidify its purpose as a meteorologic data provider to the Basin Model. For example, snow accumulation and melt were moved to the basin model since this is a land surface process. No longer do modelers have to define the same meteorologic data multiple times for different processes, like temperature data for evapotranspiration and snowmelt processes. Flexibility was also added where gridded and non-gridded data can be utilized within the same meteorologic model. Finally, a new Interpolation option was added to options within the meteorologic model and includes options for bias and lapse adjustments.

HEC-HMS has included a reservoir modeling component since the first version; however, modeling of reservoir storage and outflow was limited to structures that could be modeled using uncontrolled releases. Uncontrolled releases mean discharge is computed based on the elevation/storage and outlets in the reservoir element, regardless of the state at any other element in the model. The ability to model reservoir releases in a controlled manner was added to HEC-HMS version 4.11. The new controlled release option allows modelers to define target elevation/storage values for a reservoir component and flow targets (minimum/maximum values) at elements within the basin model. The program will go through several iterations to identify reservoir releases that meet the operation and flow targets.

Results visualization is key to understanding model results and performance. New capabilities have been added to HEC-HMS that allow the modeler to customize how model results are saved and how boundary condition data and model results, including time-series, gridded, and statistical metric results, are displayed. Spatial results allow modelers to see how precipitation and other meteorologic data fall on the watershed, and the spatial results can be viewed as gridded or subbasin average values. Tools allow modelers to plot individual grid cell information, export spatial results as raster datasets for further analysis, and to create animations for presentations. Finally, improvements made to time-series plots make it easier to create report quality plots directly from the software.