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 acres.
Slope is
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.
report suggests overland component be limited to 500 ft.

7. Sum of these two times is estimate of Tc for the area.
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 ~ 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 Routing Lag Times
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