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Dunn Sess4 101509
1. Minimum Standards For USACE Evaluation of Levee Systems For the National Flood Insurance Program Christopher N. Dunn, P.E., Director Hydrologic Engineering Center SAME 2009 Water Conference 26-28 October, 2009 Sacramento, CA
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20. Stage - Probability Derivation Initial Criteria – CNP > 90% for 0.01 event Exceedance Probability Discharge cfs) Discharge (cfs) Stage (feet) Stage (feet) Exceedance Probability 0.01
21. CNP Concepts Elevation PDF for base flood event; e.g. 0.01 exceedance event. Say 60%CNP Say 80%CNP Say 90%CNP Levee 1 – CNP = 94% Levee 2 – CNP = 83% Elev. 3 Note: PDF is NOT symmetrical; depends on Q-f, rating curve, & failure prob. Curve. Elev. 1 Elev. 2
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23. CNP Criteria Quiz 0.01 Expected WS (50% Stage) = 516.3’ 0.52 0.86 0.97 0.99 1.00 Levee Raise to El. 518’ 0.22 0.39 0.49 0.83 0.97 Levee Raise to El. 515’ 0.14 0.23 0.37 0.69 0.83 Levee Raise to El. 512’ 0.02 0.11 0.28 0.56 0.74 Levee Raise to El. 510’ 0.2% 0.4% 1% 2% 4% Plan Conditional Non-Exceedance Probability by Events
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