Bollinhurst Impounding Reservoir—Spillway Apron Leakage Remedial Works

An overflow study undertaken in 2004 identified that the spillway of Bollinhurst Impounding Reservoir (IR) had insufficient capacity to pass the Probable Maximum Flood. An overflow model test was commissioned by the owner, United Utilities, which confirmed that additional overflow capacity was required. A replacement spillway was constructed between 2010 and 2011 which incorporated the original spill weir and adjacent wing walls. During refilling of the reservoir in 2012, leakage into the new overflow tumble bay under drainage system was identified. The leakage commenced at approximately 0.5 m below overflow level and the flow, via the 160 mm diameter connecting outlet pipe, into the connecting chamber was full bore.

Works were commissioned to investigate and remediate the observed leakage following a meeting in September 2012 which included AR Panel Engineer Dr Peter Mason, subsequently appointed as QCE for the remedial works.

This paper describes the history of the reservoir, investigation of the leakage source, and the determination of possible remedial options. It also discusses the observations made during the construction works and the design of the solution to fix the leakage.