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John Griffiths, Minister for Environment and Sustainable Development

First published:
4 July 2012
Last updated:

This was published under the 2011 to 2016 administration of the Welsh Government


Following the recent extreme rainfall event, flooding and the precautionary evacuation in Pennal due to concerns regarding a local reservoir, I make this statement in response to issues raised by Assembly Members.


The safety of large raised reservoirs in Wales and England is governed by the provisions in the Reservoirs Act 1975 (1975 Act), which aims to reduce the risks posed to public safety from a reservoir or dam failure which may lead to severe flooding.


The 1975 Act seeks to ensure public safety through imposing a statutory obligation on the undertakers of reservoirs above a certain volume to take, and act on, independent professional advice on the integrity of the reservoir to manage and respond to all of the forces and conditions imposed on it. The purpose of this obligation is to reduce the risks of uncontrolled releases of water, which may lead to loss of life occurring, to an acceptable level.


The 1975 Act currently applies only to large raised reservoirs – that is, a reservoir which is designed to hold or capable of holding more than 25,000 cubic metres of water above the natural level of the adjoining ground. This threshold was set on the basis of failures of reservoirs of this size in the 1920s which caused loss of life and prompted the introduction of a 1930 Act. There are currently 1,925 large raised reservoirs in England and 201 in Wales.


Reservoirs with a raised capacity of less than 25,000 cubic metres, sometimes referred to as small raised reservoirs6, are not currently subject to any statutory safety requirements under the 1975 Act, irrespective of the possible consequences of any dam failure.


Since reservoir legislation was first introduced, there has been no loss of life through reservoir failure, however, in recent years there have been a number of near-miss incidents where lives could have been lost if the reservoir had failed. Sir Michael Pitts report on the 2007 floods in England made 92 recommendations including updating reservoir safety legislation.  


Since the Pitt review, much work has been done to improve our reservoir safety.  Reservoir inundation maps for every reservoir in England and Wales registered under the 1975 Act has now been completed.  These inundation maps which indicate the “worst realistic case” effect of a dam breach on the downstream catchment have been prepared for emergency planning purposes and show the consequences of reservoir flooding, however, they do not show the likelihood of reservoir flooding occurring.


The maps were issued to local authorities in mid December 2009 and also made available to Category 1 responders under the Civil Contingencies Act 2004.


Further to this, Schedule 4 to the Flood and Water Management Act 2010 (the 2010 Act) includes a number of provisions to updating reservoir safety legislation by amending the 1975 Act.  Chief amongst these were the reduction of the threshold for large raised reservoirs from 25,000 cubic metres to 10,000 cubic metres capacity and the introduction of the high risk designation for those large raised reservoirs thought to pose a risk to life.


To support these changes, the 2010 Act also contained a number of provisions allowing the UK Government and the Welsh Ministers to make a number of pieces of secondary legislation. These include powers to:


• determine how to calculate reservoir capacity

• substitute a different volume of water for the threshold figure

• define a structure or area to be treated as ‘large’ or define structures or areas not to be classed as a large raised reservoir, including considerations of their proximity to or potential communication with other structures or areas (cascade reservoirs)

• set the registration process

• specify the period for representations against a provisional designation and provide a right of appeal against designation

• specify the timing for inspections of large raised reservoirs

• define what is to be treated as abandonment and what is to be treated as bringing a reservoir back into use

• provide a right of appeal against a requirement to appoint an engineer and a requirement to carry out a recommendation of an engineer

• detail the assessment of the quality of engineers reports

• require people to make post incident safety reports

• prescribe a charging scheme


The primary reason for amending the 1975 Act is to ensure that appropriate safeguards are in place to protect the public. The risks from reservoir breaches are classed as low likelihood/high consequence.


Implementing Amendments to the Reservoir Act 1975


In February 2012 the Welsh Government and Defra published a joint consultation on the Implementation of the amendments to the 1975 Act.  The consultation closed on 17 May 2012 and responses are currently being considered.


A summary of responses document will be published shortly on the Welsh Government website.  It is my intention to introduce the new threshold and supporting legislation during 2013/14.


Once the amendments to the 1975 Act are introduced the Environment Agency will consider each reservoir registered under the Act and determine whether or not it is considered to be a high risk reservoir.  Those that are considered to be high risk will be designated as such and will be subject to the statutory safety regime.


Pennal, June 2012


Following the extreme rainfall event on the 8 and 9 June 2012, and the subsequent evacuation of Pennal on 10 June 2012, the Environment Agency used their powers under the 1975 Act to appoint an All Reservoirs Panel Engineer to carry out a post-incident engineering investigation of the reservoir above the village.  


A site meeting was held on the 18 June and a Post incident report incorporating any lessons to be learned from the Pennal incident will be available as soon as possible.