Concurrent risks of dam failure due to internal degradation, strong winds, snow and drought

Abstract

The chance (or probability) of a dam failure can change for various reasons such as structural degradation, the impacts of climate change and land-use change. Similarly the consequences of dam failure (flooding) can change for many reasons such as growth in the population in areas below a dam. Consequently both the chance that a dam might fail and the likely consequences of that failure can change over time. It is therefore crucial that reservoir safety risk analysis methods and decision-making processes are able to support (as a minimum) what-if testing (or sensitivity testing) to take into account these changes over time to gauge their effect on the estimated risk of dam failure. The consequences of a dam failure relate to the vulnerability and exposure of the receptors (for example, people, property and environment) to floodwater. Also the probability of dam failure varies with age, design and construction of the dam. Spillway failure may be caused by the dissipation of energy from water flowing down the spillway, and embankment erosion (scour) may be caused by a dam overtopping. The occurrence of these events depends upon the dam design and the likelihood of extreme rainfall, also in the case of overtopping wind-driven waves on the reservoir surface. In this study the meteorological situations of notable recent events i.e. the Boltby, North Yorkshire incident, 19 June 2005 in which the dam almost overtopped, and the spillway failure of the Ulley Dam near Rotherham at the end of June 2007, are studied. The WRF numerical model will be used to indicate how these meteorological situations might be maximized, and be coupled with the occurrence of other failure modes such as the likelihood of internal dam failure assessed from previous work by government panel engineers.