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