  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.
