DES 606 : Watershed Modeling with HEC-HMS

1. DES 606 : Watershed Modeling with HEC-HMS Module 2 Theodore G. Cleveland, Ph.D., P.E 29 June 2011

2. Module 2: HEC-HMS • Applications • Overview of HEC-HMS • Example 2 – A minimal HEC-HMS model.

3. Applications • HEC-HMS • Hydrologic model • Peak Flows • Hydrographs

4. Applications • Hydrograph Routing • Stream reaches • Reservoirs and detention basins • Hydrograph lagging and attenuation • Sub-basin modeling (if appropriate)

5. Modeling Principles “ … models are like maps; never final, never complete until they grow as large and complex as the reality they are supposed to represent.” Paraphrased from James Gleick “Genius: The Life and Science of Richard Feynman”

6. Modeling Principles A model is a simplification of reality – should capture the excitation-response of the system under study but only as complex as needed.

7. Hydrologic Models • Require engineering judgment • Experience helps • Results can be difficult to interpret • Require accurate input data • Judgment here too, some data have marginal influence on results, other data are vital. • Require quality control procedures

8. HEC-1 (Predecessor to HEC-HMS) • Separate (individual) programs in 1967 (L. R. Beard) • Unified into a single program in 1973 • Revised in 1981: kinematic wave • PC full version in 1988 • Revised 1991: Extended memory support • Final release 1998 • 32 years development until final release

9. HEC-HMS • Evolved from HEC-1 • Project begun in 1990 • HEC-HMS “released” in 1998 • Current version is 3.5 • 21 years of development to date. • Include the HEC-1 period and have nearly 50 years of development – The program “engine” is mature!

10. HEC-HMS • Purpose • Replacement for HEC-1 • Foundation for future hydrologic software • Improved interface (GUI), graphics, and reporting. • Newer hydrologic computation methods imbedded • Integration of hydrologic capabilities

11. Rainfall-Runoff Process • Precipitation • Meterology, Climate • Runoff • Fraction of precipitation signal remaining after losses • Watershed • Losses • Transformation • Storage • Routing

12. HEC-HMS • Hydrologic Cycle Components in HEC-HMS (circa 2008) Snowfall Evapo- transpiration Rainfall, P(t) Snowpack Snowmelt Infiltration Loss Land Surface and Vegetation Runoff Runoff Channels Reservoirs Percolation Loss Discharge, Q(t)

13. HEC-HMS • Precipitation • Abstractions • Fraction of precipitation that does not contribute to runoff (and ultimately discharge) • Routing • Watershed routing • Stream (Channel) routing • Reservoir (Storage) routing

14. HEC-HMS • Data management • Graphical User Interface (GUI) • Multiple input files • Multiple output files • Time-series in HEC-DSS • All files arranged in a “Project” • Paths to individual files • Can e-mail entire project folders and have them run elsewhere

15. HEC-HMS, IO Files • project-name.hms • List of models, descriptions, project default methods • basin-model-name.basin • Basin model data, including connectivity • meterologic-model-name.met • Meterologic model data

16. HEC-HMS, IO Files • control-specifications-name.control • Control specifications • run-name.log • Run log; messages, warnings, etc. during a run. • project-name.run • List of runs, includes recent execution time.

17. HEC-HMS • Example 2 – A minimal HEC-HMS model • Ash Creek Watershed • Use TxDOT research reports to generate certain data elements • Illustrate the data requirements and data entry for a minimal HEC-HMS model • Illustrate the conceptual similarity to the rainfall-funoff diagram and the HEC-HMS file names.

18. Summary • HEC-HMS is a computer program for rainfall-runoff modeling • A minimal model is a non-trivial exercise, requires considerable thought to generate data.