Overtopping risk assessment in river diversion facility design

Abstract

Diversion canals supplemented with upstream and downstream cofferdams are constructed to divert river flow for the construction of diversion weirs. Insufficient canal capacity leads to overtopping of water from the crest of the upstream cofferdam and sides of the diversion canal, which is regarded as the dominant risk mode in the system. A dynamic reliability model, which is based on a resistance-loading methodology with random independent loading following a Poisson process and random fixed resistance, may be used to assess the risk levels for various return periods and construction duration of a diversion weir. The system resistance is considered as the maximum canal capacity described by a lognormal probability density function. The river flow rate corresponding to a certain return period is considered as the external loading on the system. In a case study, a dynamic reliability analysis is performed for a diversion facility. From a flood flow frequency analysis, log-Pearson type 3 distribution is selected to describe the loading. The relationships between the total cost of the diversion facility, its reliability, safety, and duration of construction are examined in a decision making framework.Key words: dynamic reliability, diversion facility, resistance, loading.