| Operations & management
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 undertaking 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.
Right: This is the temporary access track that was installed which allows excavators, track dumpers and spider crane to access the base of the gorge. The route traverses through a marshland field, over a water course where a culvert crossing has been placed and into the woodland which is a SSSI. Liaising with NRW for the works in the SSSI site root protection mattresses have been implemented to allow water/air to still get to the trees root mass
www.waterpowermagazine.com | May 2023 | 15
Left: Excavator in the process of completing the ramp down into the gorge for vehicular access. The scaffolding shown in the photo is setup for pedestrian access to the base of the gorge along with a safe route for concrete pump pipework to be laid out
Craig Goch Dam facts Height
Length
Water level above sea level
Reservoir area Volume
36m 156m 317m
88ha 9,220
megalitres
Left: Small Crawler crane lifting an ROV into upstream side of reservoir to carry out desilting works to expose the valve that needs to be removed once downstream works have been completed
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