Estimating Flood Frequency and Average Annual Damage

In the National Research Council (NRC) report, “Flood Risk Management and the American River Basin—An Evaluation,” the use of expected probability (accounting for sampling uncertainty) in estimating flood frequencies and average annual flood damages, as practiced by the Corps of Engineers, was concluded to be biased. Alternative procedures recommended in the report are based on studies of samples drawn from a Gaussian population with a fixed damage function. There is no extension of the study to diverse populations (many flood locations) with different flow-damage functions, but conclusions drawn are that the recommended procedures provide frequency and damage estimates that are nearly unbiased. Rationale behind the report study is examined, and it is demonstrated herein that expected-probability procedures used by the Corps are indeed appropriate for flood-frequency estimation and for estimation of average annual flood damages.