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DES 606: Watershed Modeling with HEC-HMS

DES 606: Watershed Modeling with HEC-HMS. Watershed Subdivision Theodore G. Cleveland, Ph.D., P.E. 6 OCT 11. Watershed Subdivision. Example illustrates taking a working model, then subdividing as guided by drainage features. Base Model. Use the Woodland’s Ditch C as an example.

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DES 606: Watershed Modeling with HEC-HMS

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  1. DES 606: Watershed Modeling with HEC-HMS Watershed Subdivision Theodore G. Cleveland, Ph.D., P.E. 6 OCT 11

  2. Watershed Subdivision • Example illustrates taking a working model, then subdividing as guided by drainage features.

  3. Base Model • Use the Woodland’s Ditch C as an example. • Area is 159.3 acres. • Slope is 0.0049 • Build a HMS model and calibrate using a historical event.

  4. Base Model • For this example I choose to Kerby-Kirpich method to estimate Tc • Small watershed

  5. Base Model • For this example I choose to Kerby-Kirpich method to estimate Tc • Kerby for Overland Portion • Kirpich for Channel Portion

  6. Length Estimate • Magenta line is about 3725 feet. • 0-4696 report suggests overland component be limited to 500 ft.

  7. Time estimate • Estimate the channel portion. • Estimate the overland flow portion. • Sum of these two times is estimate of Tc for the area. • We will use this value as the estimate for Lag time in SCS-DUH

  8. Loss Model • For this example, lets use SCS CN. • Watershed is located in Woodlands, Texas. • Predominant pine forest • Lissie Sands formation • Hydrologic Soil Group B or C. • CN ~ 55-70 is appropriate • Developed portion is about 20%

  9. Observed rainfall and runoff • Have a 60 hour event in a database – stored as elapsed time. • Invent (or use actual) calendar dates

  10. HEC-HMS Model

  11. HEC-HMS Model

  12. HEC-HMS Model

  13. HEC-HMS Model

  14. HEC-HMS Model

  15. Lumped Model

  16. Subdivide • Use Grogans Mill road as guide – water would flow in swale along the road • Flow to drainage ditch from 3 areas

  17. Divide the Watershed • Use Grogans Mill road as guide • South of Grogans Mill direct to outlet. • North and West of the large pond routes to outlet • East of large pond routes to outlet

  18. Areas, Routing etc. Route 1596 ft into ditch, under road to outlet. 118.6 acres 17.7 acres 23.1 acres Route 1064 ft along swale, under road

  19. Parameter Estimates • Lag Time • Upper Watershed = 58 min. • Lower Watershed = 27 min. • East Watershed = 47 min. • Routing Lag Times • Upper To Outlet = 18 min. • East To Outlet = 13 min.

  20. HEC-HMS Model

  21. HEC-HMS Model

  22. Summary • Lumped model • Entire area is a single sub-basin

  23. Summary • Subdivided model • Selected portions of the area are linked • Joined by routing elements

  24. Summary • The two different models work about the same in this example (as compared to the observed data) • Used lag routing, but data suggest substantial storage • The large pond suggest a storage element too

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