Welsh Water invests in Craig Goch Dam maintenance

Craig Goch Dam stands at over 36m in the Elan Valley and is one of six dams split into two valleys (Claerwen and Elan) at the upper end of the River Wye catchment in Mid Wales.

Often known as the ‘top dam’, construction on Craig Goch began in July 1887 with the arrival of the railway line at the site. In the case of Craig Goch, the line had the furthest to go and a rocky outcrop had to be blasted and dug through on the route to the site, which is now known as ‘Devil’s Gulch’. Work on this masonry dam was completed in 1904, and it now stands 317m above sea level. 

Dwr Cymru Welsh Water

The Elan Valley system, including Craig Goch dam, is owned and operated by Dwr Cymru Welsh Water.  The utility company provides clean drinking water and treats wastewater for over three million people in most of Wales, Herefordshire and parts of Deeside. 

Welsh Water is unique in the water industry, as it is not-for-profit and owned on behalf of its customers, with profits reinvested for the benefit of the customers it serves. Since 2001, it has been owned by Glas Cymru which was formed in April 2001 for the sole purpose of acquiring and owning Welsh Water. The not-for-profit water company is investing heavily and working hard to ensure top quality services to all the communities it serves, and the company is investing £1.8 billion in its water and sewerage network between 2020 and 2025.

Welsh Water manages a portfolio of 140 dams of which 85 are impounding, 10 are non-impounding and 45 are potable water service reservoirs. Of the 85 impounding reservoirs approximately 75% of them are earth embankment dams and the majority are over 100 years old. 

The dams within Welsh Water’s portfolio have a variety of uses including water supply, river regulation, wildfire fighting, hydroelectric generation and amenity. 

The Elan Valley System

There are four dams on the River Elan - Craig Goch, Pen y Garreg, Garreg Ddu and Caban Coch. The River Claerwen has the newest and largest Claerwen dam, followed by Dol y Mynach dam which is a partially constructed cyclopean concrete dam. Claerwen was constructed in the 1950s but designed to have a similar aesthetic of the other Victorian dams that make up the system. 

The reservoirs have a combined storage of 99,500Ml and a combined catchment of 184km2, consisting largely of open moorland between 250m and 650m above sea level. 

The principal purpose of the reservoirs in the Elan Valley system is for water supply, and these reservoirs supply up to 364Mld (Megalitres per day) to Birmingham via a 118km aqueduct and a much smaller volume of 5Mld to a small water treatment works that serves the local area.  

In addition to supplying drinking water, there is a river regulation requirement where up to 231Mld is released from Caban Coch into the River Wye. This is based on downstream river levels and abstraction requirements.  A trial is currently being implemented to provide enhanced releases into the River Wye which will simulate spate flows and improve downstream ecology.

Investing in Craig Goch

Since autumn 2021, Welsh Water has been carrying out essential maintenance work to protect and future-proof Craig Goch Dam, and this work is being carried out in line with the Reservoir Act 1975.

Work to the Grade II Listed dam is being carried out by principal contractors, Morgan Sindall, on behalf of Welsh Water. In addition to the principal contractors, Welsh Water is also working with Whitland Engineering on the mechanical installations, Edward Diving Services and Glenfield/Varley, the valve and HPU unit suppliers and Rocksalt Subsea who carried out underwater ROV investigations and desilting. 

The work being carried out at Craig Goch is a reinstatement of the original 36” diversion pipe with downstream control to turn this into the main scour pipe. The scour is an outlet pipe at the bottom of a dam and can be opened to draw down the reservoir in emergencies or to flush sediment out of a reservoir if too much has accumulated behind the dam. Valves are used to control the flow of water through the scour.  

To complete this essential maintenance, Welsh Water is completing a number of works including the installation of a 900mm diameter hydraulic gate valve and a 900mm diameter hydraulic cone valve, as well as mechanical and electrical installations, access modifications to the dam and removal of the existing 36” gate valve from the upstream end of the pipe and replacing it with a new upturned bellmouth and trash screen. 

Phase one of the project, saw initial works to remove silt from around the 36” valve at the back of the dam. This allowed inspection to be undertaken, as well as subsequent design and planning for modifications on the 36” pipe to improve the draw down facility of the dam. A temporary access track was created in order to allow facilitate the launch of dredging equipment from the west side of the reservoir. 

Due to the need for reservoir levels to be low enough to complete the essential maintenance work on the scour outlet, phase one of the project was completed before Christmas 2022, and work is due to recommence at the site from 15th May 2023. 

Phase two of the project will begin with a drawdown of reservoir levels to allow for the work to recommence at Craig Goch. Following this, construction of the new reinforced concrete valve protection structure, the installation of the new valves, along with mechanical and electrical works and the installation of the new pipe and trash screen. Work is anticipated to be completed by January 2024.