Recent Experiences in Design and Construction of Siphons to Supplement Reservoir Drawdown Capacity

Recently there has been increasing focus on the ability of UK reservoirs to be adequately drawn-down in an emergency situation. This emergency planning has led to a growing demand for drawdown capacity assessments, consideration of the acceptable drawdown rate and, where existing facilities do not provide an acceptable drawdown, the design and construction of supplementary capacity.

It is not uncommon for the installed drawdown capacity at UK reservoirs to fail to meet the varying targets. With the reliability and adequacy of temporary solutions under question, permanent solutions are regularly preferred. As a result, the requirement for permanent improvement works such as the construction of siphon drawdown pipes is becoming prolific.

This paper shares some recent experiences in the design and construction of siphon pipes to supplement the drawdown capacity in order to achieve an acceptable drawdown rate. It presents four case studies of improvement works undertaken, including a variety of siphon options, a range of pipe diameters, pumped and suction priming systems and the use of various types of valves.

The experience presented is that of Mott MacDonald and the Mott MacDonald Bentley joint venture ‘the Principal Designer’ gained while delivering schemes for Yorkshire Water Services (YWS) and United Utilities Group PLC (UU) ‘the Clients’ assets under the AMP 5 and AMP 6 frameworks.