The use of dam break risk curves to optimise an ALARP assessment

Overview

An ALARP study has been undertaken to determine proportionate reservoir safety improvement works at the Category A Buckshole Reservoir in Hastings, East Sussex.  The study addressed a recommendation as to measures to be taken in the interests of safety following a statutory inspection in June 2016 under Section 10 of the Reservoirs Act 1975.

The inspection report concluded that the service spillway would not accommodate the design flood flow and damage to the dam during extreme flood events was likely, possibly leading to a breach failure.  The study examined a range of flood events to develop risk curves associated with the estimated likely loss of life and property damage resulting from dam failure.  Using the risk curves, it was then possible to determine the flood event that yielded the greatest incremental consequences of dam failure.

The relevant flood event in this instance was shown to be an event significantly less severe than the design flood event.  This was then used to determine the most appropriate level of reservoir safety works based on ALARP proportionality calculations.  The results of the study highlighted that the use of risk curves can provide a more accurate basis for an ALARP assessment of reservoir safety improvement works, giving an improved outcome in terms of reduction in risk and the cost to the reservoir owner.