1. WinTR-20 SensitivityMarch 20091 WinTR-20 Sensitivity to Input Parameters

2. WinTR-20 SensitivityMarch 20092 Lesson Objectives 1. Identify the various WinTR-20 Input Parameters that affect the volume of runoff and peak discharge predictions. 2. Identify the relative sensitivity of WinTR-20 to its input parameters in predicting the peak and/or volume of runoff. 3. Identify the relative sensitivity of WinTR- 20 to its input parameters in relation to channel routing.

3. WinTR-20 SensitivityMarch 20093 WinTR-20 Hydrology Model Predicts Volume of Runoff Predicts Peak Rate of Runoff Predicts Entire Hydrograph of Runoff Based on Watershed and Rainfall Characteristics Modeled as Input Parameters Changes to Input Parameters Will Change the Volume and Rate of Runoff Predicted

4. WinTR-20 SensitivityMarch 20094 WinTR-20 Watershed Input Variables Drainage Area Runoff Curve Number (RCN) Time of Concentration (t c ) Unit Peak Factor (UPF) of Dimensionless Unit Hydrograph (DUH) Antecedent Runoff Condition (ARC)

5. WinTR-20 SensitivityMarch 20095 WinTR-20 Rainfall Input Variables Depth of Rainfall Rainfall Distribution (includes duration)

6. WinTR-20 SensitivityMarch 20096 Effects of Variation in Drainage Area % Change in DA results in comparable change to predicted volume and peak of runoff. Be sure DA is being properly identified (be aware of non-contributing areas).

7. WinTR-20 SensitivityMarch 20097 Effects of Variation in RCN % Change in RCN results in exaggerated change to predicted volume and peak of runoff. RCN can be influenced by stage of vegetal growth and/or antecedent rainfall at time of storm event.

8. WinTR-20 SensitivityMarch 20098 Effects of Variation in t c % Change in t c results in decreased change to predicted peak rate of runoff (no change in volume). A decrease in t c results in an increase in predicted peak discharge.

9. WinTR-20 SensitivityMarch 20099 Effects of Variation in Unit Peak Factor % Change in UPF results in nearly similar change to predicted peak rate of runoff (no change in volume). UPF is a watershed based response to excess rainfall assumed to be similar per inch of runoff.

10. WinTR-20 SensitivityMarch 200910 Effects of Variation in Antecedent Runoff Condition (ARC) ARC values of 1 or 3 alter the RCN selected for assumed ARC 2 conditions. ARC 2 is normally assumed for design. ARC 1 can be used to help calibrate for a known “drought” condition prior to the target storm event (not necessarily accurate). ARC 3 can be used to help calibrate for a known “saturated soil” condition prior to the target storm event (not necessarily accurate).

11. WinTR-20 SensitivityMarch 200911 ARC Adjustments (Continued) For this example: DA = 1.0 mi 2, t c = 1 hr, RCN = 70, 4.0 inch 24 hr Type II Rainfall ARC 2 – (RCN 70), Q v = 1.33”, Q p = 437 cfs ARC 1 – (RCN 51), Q v = 0.37”, Q p = 65 cfs ARC 3 – (RCN 85), Q v = 2.46”, Q p = 874 cfs WinTR-20 results are very sensitive to changes in ARC. Be sure that assumed change is appropriate or alter RCN within ARC 2 conditions for finer adjustment.

12. WinTR-20 SensitivityMarch 200912 Effects of Variation in Rainfall Depth % Change in Rainfall Depth results in exaggerated change to predicted volume and peak of runoff. Be sure that the actual Rainfall that has occurred and is being calibrated to is properly identified for the entire watershed.

13. WinTR-20 SensitivityMarch 200913 Effects of Variation in Rainfall Distribution Design rainfall distributions normally set by criteria (e.g. Type I, IA, II, or III). Can attempt to calibrate to a historical rainfall event of known varying intensity (recording rain gage). Rainfall distribution alone (not depth) only effects the rate of runoff, not the volume.

14. WinTR-20 SensitivityMarch 200914 Effects of Variation in Rainfall Distribution (Continued) For this example: DA = 1.0 mi 2, t c = 1 hr, RCN = 70, 4.0 inch 24 hr Type II Rainfall Type II - Q p = 437 cfs Type I - Q p = 221 cfs Type IA - Q p = 106 cfs Type III - Q p = 383 cfs WinTR-20 peaks are very sensitive to selection of rainfall distribution. Calibrate with the best known rainfall distribution.

15. WinTR-20 SensitivityMarch 200915 Parameter Selection for Desired Change in WinTR-20 Runoff Volume WinTR-20 Parameter to be Changed, Independent of Others Desired Change in Runoff Volume (%) -50%-25%-10%-5%+5%+10%+25%+50% Required Change in Drainage Area-50%-25%-10%-5%+5%+10%+25%+50% Required Change in Rainfall-26%-13%-5%-2.5%+2.5%+5%+12.5%+23% Required Change in RCN-17%-8%-2%-1%+1%+2%+7%+13% Required Change in Time of ConcentrationN/C Required Change in Unit Peak FactorN/C N/C signifies, No Change possible to alter volume. This parameter does not effect volume prediction.

16. WinTR-20 SensitivityMarch 200916 Parameter Selection for Desired Change in WinTR-20 Peak Runoff WinTR-20 Parameter to be Changed, Independent of Others Desired Change in Runoff Peak (%) -50%-25%-10%-5%+5%+10%+25%+50% Required Change in Drainage Area-50%-25%-10%-5%+5%+10%+25%+50% Required Change in Rainfall-24%-12%-5%-2.50%+2.5%+5%+11%+21% Required Change in RCN-13.5%-6%-2%-1%+1%+2%+5.5%+11% Required Change in Time of Concentration+150%+50%+15%+7%-6%-12%-26.5%-44% Required Change in Unit Peak Factor-54%-29%-12%-6%+6%+13%+33%+72%

17. WinTR-20 SensitivityMarch 200917 Combined Parameter Impacts Assumed Normal Run DA = 1 mi 2, RCN =70, t c = 1.0 hr, UPF = 484 Runoff Volume = 1.33”, Peak Rate = 437 cfs Low Run DA = 1 mi 2, RCN =63, t c = 1.25 hr, UPF = 300 Runoff Volume = 0.92”, Peak Rate = 148 cfs High Run DA = 1 mi 2, RCN =77, t c = 0.75 hr, UPF = 600 Runoff Volume = 1.81”, Peak Rate = 904 cfs

18. WinTR-20 SensitivityMarch 200918 WinTR-20 Channel Routing Model Predicts hydrograph (including peak) at downstream end of reach. Based on cross section and reach characteristics modeled as input parameters. Changes to input parameters will change the peak discharge and hydrograph shape predicted at the end of the reach.

19. WinTR-20 SensitivityMarch 200919 WinTR-20 Channel and Reach Input Variables Selection of representative cross section Cross section rating table (slope and “n”) Channel length Flood plain length Shape of inflow hydrograph Base flow (if significant)

20. WinTR-20 SensitivityMarch 200920 WinTR-20 Channel Routing Sensitivity Test Trapezoidal cross section, BW = 15, SS = 2:1 Slope = 0.001 and 0.004 Manning n = 0.03, 0.04, 0.05 Channel length, 0.8 to 1.2 mile Inflow hydrograph, DA = 1, CN = 80, Tc = 0.5 and 1.0, RF = 3.2 inches, Type II storm Base flow = 0.0 60 WinTR-20 runs

21. WinTR-20 SensitivityMarch 200921 Two Inflow hydrographs Red (higher) is the hydrograph for Tc = 0.5 hour. Green (lower) is the hydrograph for Tc = 1.0 hour.

22. WinTR-20 SensitivityMarch 200922 Effects of Variation in Length and “n” % Change in length results in less change to predicted peak outflow. % Change in Manning “n” results in less change to predicted peak outflow.

23. WinTR-20 SensitivityMarch 200923 Effects of Variation in Length and “n” % Change in length and “n” results in less change to predicted peak outflow. Length and “n” less sensitive for Tc = 1.0 hydrograph.

24. WinTR-20 SensitivityMarch 200924 Effects of Variation in Length and “n” % Change in length and “n” results in less change to predicted peak outflow. Results for steep slope are less sensitive.

25. WinTR-20 SensitivityMarch 200925 Effects of Variation in Length and “n” % Change in length and “n” results in less change to predicted peak outflow. Results for Tc = 1.0 hydrograph are even less.

26. WinTR-20 SensitivityMarch 200926 Porcupine Mountains State Park, Michigan

27. WinTR-20 SensitivityMarch 200927 Questions???

28. WinTR-20 SensitivityMarch 200928 The End