Confidence Intervals for Flood Control Design

by T. Hromadka, Williamson & Schmid, Irvine, CA, USA,

Document Type: Proceeding Paper

Part of: Engineering Hydrology


The line drawn and labeled as the flood frequency curve is seldom identified as to what confidence is associated to the plot. For example while flood control designs are typically based on the flood frequency curve Q//1//0//0 estimate, seldom is it considered that, on the average, and with the other factors and parameters being correct, this Q//1//0//0 estimate has only a 50 percent chance of being greater than the true (unknown) Q//1//0//0 but equivalently has a 50 percent chance of being less than the true Q//1//0//0. Consequently, if the goal is to provide protection against Q//1//0//0, and this level of protection is adopted as the local policy statement for all design purposes, and there is liability should Q//1//0//0 flooding occur, then confidence intervals should be incorporated into the flood control policy statement.

Subject Headings: Flood frequency | Confidence intervals | Floods | Hydraulic design | Frequency analysis | Parameters (statistics) | Liability | Curvature

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