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Watershed Modeling using HEC-HMS and EPA-SWMM

Watershed Modeling using HEC-HMS and EPA-SWMM. ©T. G. Cleveland, Ph.D., P.E. 16 July 2012 Lesson 5. Outline. Overview of SWMM Hyetographs Precipitation in HEC-HMS Exercise: Minimal HMS Model and Texas DDF. SWMM. Storm Water Management Model (SWMM)

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Watershed Modeling using HEC-HMS and EPA-SWMM

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  1. Watershed Modeling using HEC-HMS and EPA-SWMM ©T. G. Cleveland, Ph.D., P.E. 16 July 2012 Lesson 5

  2. Outline • Overview of SWMM • Hyetographs • Precipitation in HEC-HMS • Exercise: Minimal HMS Model and Texas DDF

  3. SWMM • Storm Water Management Model (SWMM) • Started at University of Florida in the 1970’s • Continued by CDM • Continued by EPA • Started as a simple network routing model for storm water volumes and water quality.

  4. SWMM • Evolved into a legitimate hydraulics model. • Has special elements for mimic of structural BMPs Not this kind – Soviet BMP in Ukraine

  5. SWMM • Porous pavements, retention ponds, orifice and weir controls

  6. SWMM • Sub-catchment element for rainfall-runoff • Routing in conduits that are either • Open channel/Closed conduit • Normal, Kinematic, St. Venant • Lift stations • Pump curves • Junctions • Storage

  7. SWMM • SWMM is a complicated program, we will only use a part of it this class • Junctions • Conduits • Sub-Catchments

  8. Rainfall-Runoff • In SWMM rainfall-runoff is “modeled” using a sub-catchment (and a raingage and a node). • Rainfall is communicated to the program by a “gage” • Sub-catchment converts a rainfall time series into a runoff time series • Infiltration, evaporation, depression storage, etc.

  9. Minimal SWMM Model • Sub-catchment • Area, Width – Program computes “length”

  10. Minimal SWMM Model • Raingage • Sub-catchment • Outlet node

  11. Rainfall Time Series • Build a time series in elapsed (or clock time). Cut-and-paste into SWMM

  12. Minimal SWMM Model • This mimimal model will take a rainfall time series, apply to the sub-catchment, use a loss model, and generate a runoff time series at the outlet.

  13. Minimal Model Extension • After a minimal model is working, compare using one of the frequency storms from HEC-HMS • What do you need to do to copy the storm? • What about time windows (in SWMM)? • What about raingages?

  14. Summary • SWMM is an integrated hydrology-hydraulic model. • The creation of rainfall is by a “raingage” linked to a sub-catchment. • HMS output can be saved to a file then copied into SWMM • Minimal model produces similar results as HMS.

  15. Flow Width (Input Data) Flow Length (Internal Compute) Tan(a)=Slope Area=Width * Length Sub-Catchment Outlet

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