Harvard Gulch Model Background


Ben Urbonas from UDFCD has previously developed a SWMM model for the Harvard Gulch basin using 59 basins and approximately 26 junctions and routing structures. In order to simplify the model, three design points were selected at critical points and the tributary sub-basins were assigned a single raingage for analysis. This resulted in a simplified model with three ‘aggregated’ basins. HG-1 sub-basin was added to the real-time hydromodel to account for basin total effects south of Harvard Gulch.
The unit hydrographs for each basin were developed by adjusting the raingage data in the first time step to produce exactly one inch of runoff volume from the entire aggregated basin. The model computed runoff from this slug of rainfall for each individual sub-basin and routed it through the model to the selected design points. Since the definition of a unit hydrograph is the hydrograph produced by one inch of runoff, the model results at the various design points became the unit hydrograph for that basin in the real-time hydrologic model.
Muskingum routing techniques were used to route the runoff hydrographs downstream. Calibration was performed by comparing the results of the detailed SWMM model at downstream design points. The Muskingum parameters were then optimized in the Excel worksheet to match the SWMM output. The simplified Excel model now mirrors the results from the detailed SWMM model.

Methods Used
• Thiessen Polygon Rain Gage Weighting
• CUHP (Horton Infiltration Method)
• Muskingum Channel Routing

Harvard Gulch sub-basins were modeled in the Real-time model in the same configuration as the SWMM model.

Model Inputs