Spillway design, examination and failure mechanisms

This project has produced guidance on designing and examining spillways and the mechanisms that could lead to spillway failure.

Documents

Spillway design guide

Spillway examination guide

Spillway failure mechanisms guide

Project Summary

This project has produced a suite of guidance on designing and examining spillways and the mechanisms that could lead to spillway failure.

These 3 guides are designed to provide reservoir managers and undertakers as well as supervising and inspecting engineers with best practice guidance to improve safety at reservoir spillways in England and Wales.

These guides are intended to complement the following publications:

Reservoir engineers: written statements and site visit reports

Reservoir owner and operator guidance: spillways

Reservoir inspecting engineers: inspecting high-risk reservoirs.

Background

On 1 August 2019, there was a failure of the auxiliary spillway at Toddbrook Reservoir. This led to the evacuation of 1,500 people from the downstream town of Whaley Bridge in the Derbyshire High Peak area. A further spillway incident at the Oroville Dam in the USA brought attention to some of the weaknesses of historic spillway design. An independent review of the Toddbrook incident made a number of recommendations for improvement. It recommended that the Environment Agency commissioned new guidance on the failure mechanisms of spillways and how to carry out spillway inspections. This should also include guidance on spillway design based on international good practice and lessons learned from incidents in the UK.

Approach

We have prepared these guides in response to the recommendations of the Toddbrook reservoir independent review.

The guides are:

  • spillway design guide
  • spillway examination guide
  • guidance to spillway failure mechanisms

Spillway design guide

This guide covers the main design principles, methods and current best practice for the design of new spillways and upgrading of existing ones. It focuses on the design of cast-in-place reinforced concrete spillways, most typically used recently in the UK.

Spillway examination guide

This guide helps to identify safety issues as soon as possible at reservoir concrete spillways. It provides guidance on:

  • areas of vulnerability
  • observing the spillway in a range of operating conditions
  • investigating warning signs
  • monitoring change and routine surveillance

It consolidates global good practices, shares lessons from incidents and presents common and emerging techniques.

Spillway failure mechanisms guide

This guide identifies and describes the various physical mechanisms that could lead to spillway failure. These are divided into 2 broad categories:

  • stability failure mechanisms
  • structural failure mechanisms

The stability failure mechanisms have been associated with failure of the spillway or elements of it to resist uplift, overturning or sliding.

The structural failure mechanisms have been mainly discussed with reference to reinforced concrete spillways. They are associated with failure of the structure to resist the internal forces and bending moments induced by external actions and self-weight.

Project information

Project manager: Dr Chrissy Mitchell, Flood and Coastal Risk Management, Environment Agency.

This project was commissioned by the Environment Agency’s FCRM Directorate, as part of the joint Flood and Coastal Erosion Risk Management Research and Development Programme.

A Welsh translation of the summary is also available.

Published 27 June 2022
Last updated 31 October 2022 + show all updates
  1. Welsh translation of project summary added to page.

  2. First published.