Spillway design and construction innovation

Mott MacDonald Bentley Ltd (MMB) has carried out modification works to an impounding reservoir in Yorkshire, to enable the overflow system to safely pass the probable maximum flood (PMF) and maintain compliance with the Reservoirs Act 1975. The works, included lining the existing spillway and stilling basin with reinforced concrete. This logistically complex £1·8 million scheme is a key example of MMB's use of off-site construction and application of innovation to overcome significant challenges that reservoir sites can present. The reservoir has a very steep spillway, which presented MMB with a limited number of options in terms of accessing the spillway and safely constructing the proposed, ensuring a high-quality finished product. With a well-developed track record of precast concrete (PCC) construction on reservoir projects, the MMB team were inspired to push the boundaries of current design and construction methodologies. They developed a PCC ‘U-section’ product to line the spillway, installed via a unique rail and winch system. This paper describes the design and construction of the U-sections and associated installation system, including testing of the joint system to prove hydraulic performance. This design resulted in increased speed of construction, reduced costs and zero injuries on site.