New View of Flood Frequency Incorporating Duration

Abstract

Most flood risk studies quantify flood likelihood and damage as functions of depth. The length of time that a flood remains above a stage (duration) is also necessary to quantify infrastructure vulnerability. The proposed approach adds a second dimension, time, into flood risk studies by developing a joint distribution of flood stage and event duration. Bivariate flood frequency model metrics are developed; the metrics are illustrated using data from four gauged sites, two riverine and two tidal. It is concluded that a general joint distribution model is applicable to both riverine and tidal sites. A minimum time between events (interevent time) determines the assignment of sequential periods to a single event or multiple events; this measure is shown to affect the statistics of the tidal sites, but not the riverine sites. The flood stage-duration-frequency curves developed in this study demonstrate a new approach that allows stakeholders to consider the coupling between depth and duration, and thereby develop preparedness and response plans that address temporal aspects such as time out of service in addition to depth-dependent damages.