1. Hydrologic Analysis Dr. Phil Bedient Rice University

2. Mansfield Dam - Lake Travis Unit Hydrographs S Curve Method Synthetic UH Multi-period storms UH Applications Kinematic Wave

3. Hydrograph computed at outlet of each subarea

4. Hydrographs routed to the outlet of the watershed

5. Hydrographs routed thru one reach of the watershed I – Q = dS/dt

6. Distribution of Rainfall Infiltration Detention Storag e Depression Stora ge Direct Runoff

7. Net Rainfall Rising Limb Crest Falling Limb Recession Base Flow Direct Runoff DRO Hydrograph Relations

8. Base Flow Methods Straight Line ABC continue the recession - concave Empirical method

9. 1. Horton Method  Method 3. Initial and Constant Loss Infiltration Loss Curves

10. Typical Rainfall and Hydrograph Response

11. Time-AreaMethod Watershed Isochrone Hyetographs Time Area Histograms Add and Lag Method Resulting Hydrograph

12. Time Area Hydrograph P1 * A1 P2*A2 + P1*A2 P3*A1 + P2*A2 + P1*A3

13. Unit Hydrograph Linear Methods Tested in numerous WS Stood the test of time Regional calibration Still most used approach Basin response from 1 inch of uniform rainfall of given duration, D

14. Measured Hydrograph Adjusted for Net RF Adjusted for Net Rainfall Of 1 Inch 2 inches

15. Base Flow and Infiltration Subtract BF Subtract Infiltration Determine Net Rain Integrate hydrograph Adjust hydrograph ordinates to match net rainfall Vol Determine UH Infiltration Net rainfall Peak Flow

16. D = 2-Hr Unit Hydrograph Adjusted Net Rainfall one inch over basin QpQp

17. Change UH Duration Consider 1 hr UH Add and Lag two UH by one hour Sum and divide by 2 Results in 2 hr UH

18. Equilibrium Hydrograph Uniform Rain Inflow = Outflow Equiv to summing n hydrographs in T Produces S curve One Hydrograph

19. S-Curves for UH

20. S-Curves Convert 2 hr Unit hydrograph to 3-hr Lag each 2-hr UH by Duration D Add to produce S curve S-curve

21. Lag by D’ and subtract both curves Lag S Curves in time, subtract them, and multiply by D/D’

22. 3 hr. Unit Hydrograph from a 2 hr. UH (D/D’) 3 HR UH

23. Hydrograph Convolution 1 2 3 312 Add up the ordinates of all three to produce storm hydrograph STORM HYDRO Add and Lag Method

24. Multi-PeriodStorm P g - F = Net Rainfall RF units = UH duration (i.e. 1 hour) Adjust UH by Net RF Add and Lag UH Produce Storm Hydrograph UH STORM NET RF

25. Development Effects on UH NaturalPartialFully Developed

26. Actual Brays Bayou UH Faster response with Development Higher peak flow with Development Need to provide down- Stream capacity 1959 Present Ultimate

27. Synthetic UH Developed for basin that were ungaged Based on data from similar gaged basins Most methods are very similar in nature Revolutionized ability to predict hydro response 1959 Present Ultimate

28. Synthetic UH Methods Methods to characterize ungaged basins Use data and relationships developed from gages Variety of approaches but most based on T p and Q p England and U.S. led the efforts to standardize UH

29. Synthetic UH Methods Snyder’s Method (1938) Clark Method (1945) Nash (1958) SCS (1964, 1975) Espey-Winslow (1968) Kinematic Wave (1970s)

30. Snyder’s Method 5 to 7 points

31. SCS Methods Triangular UH Dimensionless UH

32. SCS Triangular UH Example 1 inch of RF over 1.6 hr duration

33. 2-hr Duration UH Example Q p at 400 cfs at 10 hr with 24 hr T b Six Hours of Uniform Rainfall = 0.25 in/hr 1.5 Inches Total Rain 2 4 6 8 10 12 14 16 18 20 22 24 26 30 100 200 300 Time in Hours 400

34. SCS RAINFALL RUNOFF CURVES

35. Unit Hydrograph Applications

36. Land Use 1 Land Use 2 Unit Hydrograph Changes Land Use will alter UH Peak and Timing

37. Kinematic Wave Overland Collector Channels Main Stream Manning’s Eqn

38. Kinematic Wave

39. Basin hydrographs- routed & combined to produce storm hydrograph Basin hydrographs- routed & combined to produce storm hydrograph