Probability of Flood-Induced Overtopping of Barriers in Watershed-Reservoir-Dam Systems

Abstract

An engineering methodology is developed to build hazard curves to evaluate the probability of flood-induced overtopping of barriers in watershed-reservoir-dam systems. The probable maximum precipitation in the watershed under consideration and its distribution in time during the acting storm is estimated. Considering the effects of the local geology, soil, topography, and land use, a random representation of the storm hourly rain is translated into effective runoff, including losses due to evaporation, interception, and surface retention. The uncertainty in the hydrological characteristics of the drainage basin is captured by a random time to concentration. Random hourly unit graphs are constructed analytically for a convex watershed and convoluted with the storm time-history to result in the random hydrograph for the inflow flood into the reservoir of the dam system. Flood routing through the reservoir is then computed with or without noise in the model. The deterministic path leads to a hydrograph for the water level at the barrier upstream face. The stochastic path evaluates through simulation the probability density function of variates (at discrete times) of the nonstationary random process of this pool level. The characterization of the reservoir-pool maxima allows the estimation of the probability of barrier overtopping.