Influence of initial reservoir level and gate failure in dam safety analysis. Stochastic approach

Abstract

This study proposes a stochastic methodology to assess the influence of considering variable reservoir levels prior to the arrival of floods in hydrological dam safety; introducing probability associated to gate failure scenarios. The methodology was applied to the Riaño dam (northern Spain) by analyzing the effects of incoming floods with return periods ranging from one to 10,000years. We studied four scenarios with different gate failure rates and compared the results assuming initial reservoir level equal to the maximum level allowed in the reservoir under normal operation conditions with those considering variable initial reservoir levels. The ratio of the return periods associated to different reference levels reached in the reservoir considering variable over constant initial level ranged from 2.0 to 4.1. The ratio of the return periods obtained assuming gate failure and no failure for the same reference reservoir level ranged up to 93, 160 and 240 depending on the gate failure rate assigned. The ratio of the return periods associated to different maximum spillway discharges considering variable over constant initial reservoir level ranged from 2.5 to 6.1. However, the ratio of the return periods obtained assuming gate failure and no failure for the same discharge ranged from 0.7 to 1.1, showing no influence of gate failure. For the study case, our analysis highlighted the importance of considering the fluctuation of the initial reservoir levels and different gate failure scenarios, emphasizing that the return periods of maximum levels reached in the reservoir and maximum outflows are the variables that best represent dam and downstream hydrological safety.