Engineering planning and design of a local flood warning system should
include a reliability analysis. The reliability of warnings can be qu
antified in terms of the relative operating characteristic-a relation
between the probability of detection and the probability of false warn
ing of a zone of the floodplain-and its transformation, the performanc
e trade-off characteristic-a relation between the expected number of d
etections and the expeced number of false warning per year for a zone.
Numerical procedures are derived for computing these two characterist
ics. Two case studies in Pennsylvania are reported. The case of Milton
, a town on the West Branch of the Susquehanna River, demonstrates fun
damental tradeoffs between the reliability and the lead time of warnin
gs. 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 Crops of Engineers and the river f
orecasting technology of the National Weather Service.