RELIABILITY-ANALYSIS OF OPEN DRAINAGE CHANNELS UNDER MULTIPLE FAILURE MODES

Open drainage channel design involves variables that are uncertain. Because the performance of the channel system is also uncertain, reliability analysis is used to measure the reliability of the system performance. In this paper, the reliability of open drainage channels under three possible failure modes is examined. The first failure mode occurs when the runoff exceeds channel capacity. The runoff and channel capacity are random variables that are estimated using the rational method and the Manning equation, respectively. The second failure mode occurs when the actual now velocity exceeds the maximum allowable velocity for erosion control. The third failure mode occurs when the actual flow velocity is less than the minimum allowable velocity for deposition control. The minimum and maximum allowable velocities are considered random variables. The failure probability of each mode is estimated using the advanced first-order second-moment (AFOSM) method. The overall failure probability of the system that accounts for the correlations between the failure modes is presented. The method was applied to an example and was verified using Monte Carlo simulation. In practice, the method can be used to find the reliability of an existing channel under multiple failures, to evaluate the effects of alternative improvements, and to design a new channel for a specified reliability level.