Geospatial Hydrologic Modeling Extension (HEC-GeoHMS)

The Geospatial Hydrologic Modeling Extension (HEC-GeoHMS) has been developed as a geospatial hydrology toolkit for engineers and hydrologists with limited GIS experience. HEC-GeoHMS uses ArcView and the Spatial Analyst extension to develop a number of hydrologic modeling inputs for the Hydrologic Engineering Center‘s Hydrologic Modeling System, HEC-HMS. ArcView GIS and its Spatial Analyst extension are available from the Environmental Systems Research Institute, Inc. (ESRI). Analyzing digital terrain data, HEC-GeoHMS transforms the drainage paths and watershed boundaries into a hydrologic data structure that represents the drainage network. The program allows users to visualize spatial information, document watershed characteristics, perform spatial analysis, and delineate subbasins and streams. Working with HEC-GeoHMS through its interfaces, menus, tools, buttons, and context-sensitive online help allows the user to expediently create hydrologic inputs for HEC-HMS.

HEC-GeoHMS can also generate tables with information on the physical characteristics of water bodies and watersheds. This information is useful when estimating hydrologic parameters.

Additional features include:

• Data Management: This feature aids in managing the locations of different projects and can also be used for error checking and detection
• Terrain Preprocessing: This can be done in two modes: step-by-step or batch. In step-by-step mode, the user can examine the model outputs and modify the data set as needed. If the user is confident in their data set, they can opt to run this feature in batch mode which eliminates additional steps and runs unattended.
• Basin Processing: The user can divide the basin into subbasins (or merge subbasins together) with the results displayed instantaneously. This allows the user to make modeling decisions on the fly, rather than waiting until the end to run the model and then make modifications.

Basic Inputs:

• Watershed and subbasin information (boundaries, sizes, stream locations, etc)
• Pre-preared data to apply over the watershed grid
• Topographical features and drainage information

Basic Output:

• Spreadsheets and datasets describing watershed and subbasin characteristics
• Spatial analysis result datasets
• 2-D and 3-D images including topography, and stream and water body locations
• Data that can be imported for simulations run in HEC-HMS

How to Run the Model:

• Import or construct a watershed with subbasins. You can import a file made with HEC-HMS, or use HEC-GeoHMS to build a new one.
• Modify the watershed, subbasins, and their characteristics as needed
• Import pre-assembled data to associate with the site. Be sure that the data is compatible with GIS data structures. If you are unfamiliar with GIS data analysis methods and techniques, you may wish to read over some examples in the HEC-GeoHMS users manual.
• Run a simulation/ perform you analysis and view the results. You may also export the data to HEC-HMS to perform additional hydrologic modeling

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