Hydrologic Modeling with HEC HMS and QGIS

Data and Downloads

Download HEC-HMS here: https://www.hec.usace.army.mil/software/hec-hms/downloads.aspx Download QGIS here: https://qgis.org/en/site/forusers/download.html

Data Sets

1. Terrain and Map Data in QGIS - this could include: country borders, river basin areas, rivers and streams, elevation models, etc. Terrain data types: .shp, .tif.

Method

1. Start HEC-HMS and create a new project. Name the project according to the desired watershed model. Choose a location to save the project. Set the Default Unit System to U.S. Customary or Metric (unit types can't be changed for a single element, units must be uniform throughout the project elements)
2. Use file explorer to copy relevant GIS data sets into the "maps" directory within the project folders from step 1.
3. To add terrain data: Select components > terrain data manager > new. Name the new terrain according to the datasets/watershed.
4. Create River Basin: Components > Create Component > Basin Model > New. Name the basin according to the watershed. The river basin and terrain data will automatically be linked.
5. Set appropriate coordinate system for desired river basin: GIS > Coordinate System.
6. Use built-in GIS delineation tools (this can also be done separately in QGIS or ArcGIS), to delineate the watershed into subbasins and reaches (streams). 1) GIS > Preprocess Sinks. 2) GIS > Preprocess drainage. 3) Identify streams. The tool for this step can either generate streams OR reference a shapefile of streams from the maps directory in step 2. GIS > Identify Streams. 4) Break points. This step dictates the discharge point for the stream system (the start of the delineation). GIS > Break Points Manager > Create New outlet. 5) GIS > Delineate elements.
7. Merge desired elements. Only two elements may be merged at one time. Start at the outlet of the water shed and merge elements by pressing shift and right clicking each element. Each merged subbasin, reach, or junction should have at least one upstream connection. Delete any unnecessary junctions or unconnected elements.
8. Add time series meteorological elements. Components > Create Component > Time-Series Data. New gages can be created for various elements such as precipitation, snowmelt, evapotranspiration etc. Data can be entered manually or via HEC-DSS.
9. Create a meteorologic model: Components > Create Component > Meteorologic Model. Name the model based on the meteorological event or time period being modelled. Add meteorologic elements according to desired method/parameters under the meteorological model tab. Check to make sure subbasins are included in the meteorologic model: Meteorologic Model > Basins > Include Subbasins > Yes.
10. Link meteorologic elements to subbasins. Options include: evapotranspiration, precipitation, snowmelt, and any other meteorological time series data entered in step 8.

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