1. Hydrologic Calibration: October 2010 U PDATE OF E FFECTIVE H YDROLOGY FOR M ARYS C REEK

2. Agenda Background Hydrologic model Hydrologic calibration 100-year discharges, Existing Conditions

3. Background Largest contributor to the Clear Fork of Trinity River 55.2 mi 2 Drainage area of Clear Fork at the confluence is 8.5 mi 2

4. Aerial View Marys Creek Clear Fork Trinity River

5. 100-year Floodplain Marys Creek Clear Fork Trinity River

6. DFIRM

7. Effective WSEL Profile Marys Creek Clear Fork of Trinity River

8. Effective Hydrology Used NuDallas 37 subbasins 15-min time step Initial and constant loss Snyder’s UH Location Drainage Area (mi2) 100-yr Discharge (cfs) Marys Creek At Confluence56.04 42,800 Clear Fork Upstream of Confluence 8.513,000 Downstream of Confluence 63.2 25,400 FIS

9. Purpose of Study Update the flows on Marys Creek and the Clear Fork of the Trinity River. Phase I Create a new hydraulic model to analyze the confluence of Marys Creek with the Clear Fork. Phase II Remap the 100-year floodplain at the confluence

10. Hydrologic Model HEC-HMS 49 basins Routing – Modified Puls (main streams) – Muskingum Cunge (smaller streams) Losses and Unit Hydrographs – Initial and constant with Snyder’s U.H. – Curve Number and SCS U.H. 5-minutes time step

11. Subbasins

12. Historical Events, June 2000

13. Historical Events, June 2004

14. Historical Events, March 2007

15. Calibrated Rainfall

16. USGS Gage, Rating Curve Based on field measurements up to a stage of 6 feet Extrapolated above 6 feet

17. USGS Gage, Rating Curve

18. Adjusted Discharges, June 2000

19. Adjusted Discharges, June 2004

20. Adjusted Discharges, March 2007

21. Hydrologic Calibration Adjust hydrologic model to match the observed (adjusted) discharges Match basin response by adjusting – Infiltration losses – lag times Very time consuming

22. Calibration

27. Hydrologic Calibration, June 2000

28. Hydrologic Calibration, June 2004

29. Hydrologic Calibration, March 07

30. Frequency Events Snyder’s – Average lag times – Average constant losses – Initial loss: 2 inches SCS – Average lag times – CN (II) – Initial loss: default (0.2S) Frequency Rainfall – ISWMM (USGS)

31. 100-year, Existing Conditions

32. Flow Comparison FIS: 42,800 cfs Snyder’s: 31,700 cfs SCS: 31,200 cfs

33. Summary More accurate hydrology for Marys Creek based on calibration of 3 historical events Lowered peak discharges by about 25%

34. Questions