Burnhope Reservoir: improving drawdown capabilities and water network resilience

A statutory inspection of Burnhope Reservoir completed under Section 10(3) of the Reservoirs Act 1975 noted that the 30 inch washout valve at the outlet tunnel portal had not been tested for some time. A measure in the interests of safety was to simply open and close the 30 inch washout valve over its full range to prove its operability. However, the washout valve is located on the outlet of the 40 inch supply main, which provides both a raw water supply to the water treatment works (WTW) and can also be used for emergency drawdown. Should the washout valve fail, the consequence would be a loss of pressure to the WTW, which would shut down. To maintain deployable output throughout the testing of the washout, its subsequent replacement and installation of a new free discharge control valve, a new 600 mm cross-connection pipeline was installed between the independent 40 inch supply/emergency drawdown main and 30 inch scour main. This cross-connection pipeline then removed the risk of interrupting the water supply and permitted the washout to be tested and subsequently replaced while also providing a resilient water network and much improved control of the 40 inch supply main drawdown asset.