Reliability of Flood Warning Systems

Engineering planning and design of a local flood warning system should include a reliability analysis. The reliability of warnings can be quantified in terms of the relative operating characteristic—a relation between the probability of detection and the probability of false warning for a zone of the floodplain—and its transformation, the performance trade‐off characteristic—a relation between the expected number of detections and the expected number of false warnings per year for a zone. Numerical procedures are derived for computing these two characteristics. Two case studies in Pennsylvania are reported. The case of Milton, a town on the West Branch of the Susquehanna River, demonstrates fundamental trade‐offs between the reliability and the lead time of warnings. The case of Connellsville, on the Youghiogheny River, demonstrates synergistic gains in warning reliability due to a coupled solution: a flood‐control dam of the U.S. Army Corps of Engineers and the river forecasting technology of the National Weather Service.