Lower Bretton Dam: Ensuring function while protecting heritage

The construction of Lower Bretton dam was completed in 1782 to form an amenity lake in the grounds of the Bretton Hall estate and impounds a reservoir which is the lower of a cascade of two. The River Dearne flows past the two reservoirs in a substantial channel on the left bank and all except extreme floods bypass the reservoirs and flow down a large, Grade II listed, masonry cascade routed down the left mitre of the lower dam. The right hand wall of the masonry cascade supports the toe of the dam embankment.

A Reservoirs Act Section 10 inspection in 2012 identified a number of measures to be taken in the interests of safety. The most important were related to substantial damage to the masonry cascade and concerns with the spillway flood discharge capacity. The Inspecting Engineer recommended emergency repairs to the cascade together with a new flood study and physical modelling to more accurately assess the hydraulic performance of the dam.

The paper describes the approach to the design and construction of the remedial works to this High-Risk reservoir. These included sympathetic modifications to the approaches to the main and auxiliary overflows to improve the discharge characteristics, reconstruction of the cascade wall, and repair of the masonry cascade. The paper also sets out the construction challenges faced during the abnormally wet winter of 2015-16.