Overtopping Reliability Models for River Levee

Abstract

Wind setup and wave run-up heights are important considerations in determining the total height of a river levee system. In this study, two generalized reliability models for a levee system are developed considering the inherent uncertainties associated with wind as well as hydrologic and hydraulic processes. The generalized models can be simplified to reliability models when only hydrologic and hydraulic uncertainties are incorporated. By using the concept of a wind-flood damage ratio, reliability values of a levee system can be obtained and discussed on the same economic basis. A higher ratio of wind-flood damage requires a higher total levee height to obtain the same reliability value as for a lower wind-flood damage ratio. The total reliability decreases with an increase in service period of the hydraulic structure and/or the wind-flood damage ratio if the total levee height remains the same. The models enable the performance of a levee system to be predicted in terms of reliability. When the total levee height is specified, different options exist for the flood levee height to protect flood overtopping and for the freeboard allowance to withstand wind-generated wave overtopping. The best option can be chosen on the basis of a maximum reliability value. An example application of the models shows how the flood levee height and freeboard allowance may be determined to yield maximum reliability.