BRE BR303 PDF

Scope of this guide

This guide provides information relating to methods which can be employed to identify and investigate defects in embankment dams. Some of the more common methods used to effect repairs are described. The guide also lists relevant references covering published papers and other guidance documents and contains an Appendix which gives more detail on the use of tracers for leakage detection.

The guide is intended to assist all those responsible for the safety of reservoirs which are impounded by embankment dams. This includes personnel who visit the reservoir site in the course of their duties, private owners and their professional advisors, the staff of the statutory undertakers who own or operate reservoirs, the enforcement authorities who may also be reservoir owners, engineering staff and technicians of consulting engineers, as well as Supervising Engineers and Inspecting Engineers appointed under the Reservoirs Act 1975.

The guide is neither a mandatory document nor a code of practice. Every reservoir is unique and qualified civil engineers with responsibilities for reservoir safety under the provisions of the Reservoirs Act 1975 must always exercise their professional knowledge, experience and judgement and should not feel constrained by the guidance in this publication.

Investigations of embankment dams and their interfaces with ancillary structures are undertaken as part of the continuing process of safety evaluation and the guide is focused on the following features.

Technical factors

The guide is primarily concerned with technical factors associated with the performance of embankment dams rather than with the regulatory framework in which dam safety is conducted. In Britain the safety of dams is regulated by the Reservoirs Act 1975 which was not fully implemented until 1986/1987 and this Act applies to all reservoirs designed to hold, or capable of holding, more than 25 000 m3 of water above the level of any part of the land adjoining the reservoir. While the report has been written with the British situation in view and in places refers to the British regulatory system, much of the report has a wider application.

Safety of existing dams

The guide is concerned with the evaluation of the safety of existing embankment dams and not the design and construction of new structures. In the past the design and construction of new dams has received most attention from dam engineers as a large investment is made at this early stage and major resources are available. Potentially hazardous features can be eliminated at the design stage. With a reducing amount of new dam construction in many parts of the world and an ageing population of dams, the evaluation of the safety of existing dams has become increasingly significant for dam engineers. In the 1992 Geoffrey Binnie Lecture, Dr Pircher, then President of the International Commission on Large Dams, remarked that, under the dominant keyword of safety, such matters as surveillance, operation, maintenance and, where necessary, preventive and remedial measures, will account for a steadily growing proportion of the workload of dam engineers (Pircher 1992) and added:

‘Though less spectacular than the field of design and construction, this task also demands outstanding expertise and continuity in management.'

Safety against catastrophic failure

The storage of a large quantity of water above a populated area represents a potential hazard to the population downstream and a very low risk must be established where public safety is involved. The guide is concerned with ensuring safety against catastrophic breaching of the embankment resulting in an uncontrolled discharge of water, rather than with the loss of operational capacity.

Deterioration and ageing

A dam may be, or may become, unsafe due to many factors including:

• some defect in the original design or construction,
• the inability to withstand an extreme natural event not envisaged in the original design, 
• the inability to withstand operating conditions more adverse than those previously encountered and not envisaged in the original design, 
• some process of ageing, and
• poor or little routine maintenance over an extended period.

The guide is concerned with safety against defects in, and deterioration of, embankment dams rather than with safety against extreme natural events such as major floods and earthquakes.

Embankment performance

The guide is concerned with embankment behaviour and not with the deterioration of ancillary works as such. However, embankment problems are often associated with the interface between the embankment and an ancillary structure and these situations are addressed as are situations where the deterioration of ancillary works could affect the embankment. This guide is concerned with malfunctioning within the body of the embankment and does not consider superficial damage, such as damage to the upstream slope protection or wave wall.