1. Parameter Sensitivity in Hydrologic Modeling Tanya Hoogerwerf March 7 th, 2002

2. Outline  Flood discharge calculation overview  Problem statement and research objectives  Case studies  Sensitivity analysis of hydrologic parameters  Conclusions

3. Flood Discharge Calculation

4. Soil Type and Land Use Hydrologic Modeling Parameters SLOPE Longest Flow Path (LFP) AREA Slope Longest Flow Path Area Soil Type and Land Use (CN)

5. How Are Parameters Calculated? Level 1: From Paper Maps (Traditional Method) Map Wheel Planimeter Level 2: From Scanned Maps

6. How Are Parameters Calculated? Level 3: From Grid-Based Digital Elevation Models (DEMs) Level 4: From Triangulated Irregular Networks (TINs)

7. Lag Calculation Soil Type and Land Use SLOPE Longest Flow Path (LFP)  L w is Longest Flow Path  CN is Curve Number (derived from Soil and Land Use Data)  s is slope SCS Lag Formula (1972)

8. Flood Discharge Calculation SCS Lag Formula (1972) Q t Q peak

9. Problem Statement Differences encountered in lag results between traditional methods and automated methods Traditional MethodsAutomated Methods

10. Research Objectives  For traditional and automated processes, determine  Sources of error  Range of errors  Significance of errors

11. Outline  Flood discharge calculation overview  Problem statement and research objectives  Case studies  Sensitivity analysis of hydrologic parameters  Conclusions

12. What Was Used to Test?  Set up the four levels of case studies  3 differently sized areas 0.5 mi 2 8.8 mi 2 1.6 mi 2

13. Determination of Parameter Sensitivity % change in slope…% change in lag…% change in Q

14. Case 1: Measurement From Paper Maps

15. Case II: On Screen From Raster Maps

16. Case IIIA: 10m and 30m Digital Elevation Models, Using GIS/CRWR-PrePro

17. Case IIIB: 10m and 30m Digital Elevation Models Using WMS

18. Case IV: Automated Methods Using WMS and a Triangulated Irregular Network Model (TIN)

19. %C v =  /  Case Study Results

20. Outline  Flood discharge calculation overview  Problem statement and research objectives  Case studies  Sensitivity analysis of hydrologic parameters  Conclusions

21. Elasticity As a Measure of Sensitivity  Elasticity is dimensionless  Provides measure of sensitivity  <1 is “inelastic”  >1 is “elastic” y x X* Y*

22. LAG Longest Flow Path Analytical Calculation of Gradients Q t  As the longest flow path varies by 13.2%, the lag varies by 10.6%  The elasticity is 10.6/13.2 = +0.80…inelastic 13.2% 10.6%

23. % Change in LAG Discharge (Q) Numerical Calculation of Gradient Q t 10.6% -3.04% Elasticity =-0.29

24. Sensitivity Results % change in parameter…..% change in lag…..% change in Q

25. Elasticity SLOPE LONGEST FLOW PATH (LFP) CN

26. Elasticity AREA CN

27. Conclusions  Automated methods using grid-based DEMs are less time consuming than traditional methods…USE AUTOMATED METHODS  Slope and longest flow path measurements do not greatly influence discharge  Measurements of area do not vary greatly, spend time/resources obtaining accurate soil and land use data for CN

28. ~Thanks ~ Dr. Maidment David Stolpa Dr. Charbeneau Dr. Barrett Dr. Nelson CRWR Group EWRE Friends Environmental Modeling Systems, Inc.