Spillway design and inspection - Some practical guidance

Overview

The recent failures of the spillway chutes at Oroville in the USA and at Toddbrook in the UK have once again highlighted the importance of these structures to the safe operation of our dams and reservoirs. It has also illustrated their potential vulnerability and need for experienced design and maintenance. In fact, these failures follow others in the UK in the not-so-distant past such as the masonry chute failures at Boltby and Ulley and also elsewhere in the world. Perhaps more surprisingly in all these cases was that the failures occurred at floods far below their supposed design capacities. While the floods involved in each case could be described as unusual, they were by no means extreme.

The design of spillways is a particular speciality. Spillways are one part of our dams where structural engineering, material properties, hydrology, hydraulics and hydrodynamics, geology and rock mechanics and sometimes mechanical and electrical engineering, all need to work together for the spillway to be successful. In some cases, the cost of constructing a spillway can be almost as much as the cost of the main dam wall and yet it is also the one aspect of dam engineering for which formal UK design guidance is lacking.

In the presentation Dr Mason will outline the hydraulic and other factors needed for the sound design of spillway chutes. This will focus mostly on concrete chutes and on both rock and soil foundations. It will also touch briefly on stepped masonry chutes and on the selection of terminal, energy dissipation structures. Some guidance will also be given on Inspection and maintenance aspects.