Trebeddrod – A case study on the construction of a small spillway at a constrained site

Following recent re-categorisation of Trebeddrod Reservoir to a Category A dam a new spillway was required to safely pass the Probable Maximum Flood (PMF) outflow of 28.7m³/s. The small and constrained nature of the site, along with the limited access and working space governed many aspects of the design and construction of the spillway.

The works at Trebeddrod were planned and designed with a degree of flexibility to enable the contractor to use his experience to develop the most suitable construction methods for the constrained conditions. At the design stage a continued role for the designer was agreed. The resulting collaborative approach to the works enabled various aspects of the design to be further developed and modified during the works, to suit the contractor’s favoured approach to construction.

This paper presents some examples of how the design and contracting teams worked together, and adopted some innovative approaches during construction, to successfully complete the new spillway.