Clydach Reservoir
Clydach reservoir near St Gwynno Forestry was built in 1892 to provide drinking water for the local area. However, we have changed the way we supply water to local communities over the years and the reservoir was disconnected from our network 30 years ago.
Unlike other reservoirs, this site is also too small to store any significant amount of water during stormy weather to help reduce flooding. As a result, maintaining and investing in reservoirs to meet current reservoir safety standards, when they are no longer needed, does not represent the best use of customer money. This is why we have been exploring options on how best to return Clydach reservoir close to its natural state, while also using this opportunity to improve the local environment by minimising the impact of this man-made structure on the local ecology and biodiversity.
What will we be doing?
By returning it close to its former state, this would involve reducing water levels to create a natural waterway through the area now taken up by the reservoir. We have examples of other sites where this has been done successfully by working with the local community to ensure it is in keeping with the surrounding landscape. There’s an illustration enclosed of how Clydach reservoir could look after we complete this work. There’s a lot of research and work that needs to be done before any improvements can be made. Once these have been confirmed we will be consulting the local community over coming months on various options on how best to ensure that the site is safe, but also more accessible to residents as it is currently private land with parts of the site being inaccessible.
Environment
Protecting the local environment will be key to this work. We are working closely with Natural Resources Wales and specialist environmental consultants with detailed ecological surveys, and assessments being undertaken to ensure that any changes made do not have a negative impact on the environment. We will keep residents and interested groups informed of this work.
The illustration is how Clydach reservoir could look after we complete this work. There’s a lot of research and work that needs to be done before any improvements can be made and we will be consulting the local community over coming months on various options on how best to ensure that the site is safe but also more accessible to residents as it is currently private land with parts of the site being inaccessible.
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Frequently asked questions
All dams have a level of risk associated with them which is why all DCWW’s dams undergo regular surveillance and monitoring to ensure their safety. They are also subject to regular supervision by specialist dam engineers. While the dams to be discontinued are currently as safe as can be for their age, as with all structures, significant investment is needed to ensure they continue to meet safety standards. Since these dams are no longer needed for operational purposes, this is not considered to be a worthwhile investment of our customers money.
There are no current plans to discontinue any other local reservoirs.
Any group who takes over the running of the reservoirs (known as the ‘Undertaker’ in the Reservoir Act 1975) has a legal duty to comply with the requirements of the Reservoir Act 1975. This includes being responsible for all the operational and capital costs. It is therefore not considered feasible for a local group to become the undertaker.
The reservoirs currently fall under the ambit of the Reservoir Act 1975. This means owners must legally ensure the safety, ongoing surveillance, monitoring, and inspections of the dams as well as any mandatory Capital works needed on the dams. The costs associated with this very often run into the millions of pounds. It is therefore not considered feasible to sell the sites to local people / groups.
Once we have completed our work, where possible we will make the site accessible for the local community to enjoy. This could mean creating walkways which are not currently in place if the site is an operation site and therefore not accessible to the public.
This is decided on a site-by-site basis by the local authority. In all cases DCWW consults with the local authority to ensure that any work is certified as lawful.
There is a thorough list of reservoirs that are made available to NRW to assist in fighting forest fires. This list changes from summer to summer based on whether a site has works ongoing or activities that would prevent it from being used. There are several far larger reservoirs available to NRW and the Fire service within a 2-minute flight from the area of Clydach reservoir.
The sites will be left to re-naturalise with minimal human intervention. DCWW will continue to be responsible for the sites and any maintenance that may be required.
The Reservoir Act 1975 includes the term ‘discontinuance’ which is where the reservoir is altered so that it is incapable of holding 10,000m³ or more of water. In simple terms discontinuance means removing the structure which holds water above natural ground. In some cases, discontinuance will involve returning the area back to a river, in others it will mean returning the area back to a natural lake (instead of an artificially raised one).
Ecological surveys have been carried out at the sites to assess the fish and wildlife of the reservoirs. Dam removal is an effective way of improving fish migration, helping fish populations to flourish as well as improving the biodiversity of the area. Mitigation will be in place to ensure existing wildlife is not harmed. For example, floating wetlands will be installed at sites where water voles may be present. We work collaboratively with Natural Resources Wales and other ecological partners to ensure wildlife is protected before we commence any work.
The removal of the manmade dam structures will change the landscape back to its natural state before the dams were built, whether that be back to a river or natural lake. This is a betterment in terms of biodiversity, the natural environment and public safety.
The reservoirs that are being discontinued no longer form part of the water network or are used for supply. They are aging assets and present significant ongoing costs in maintaining them to the required safety standards. This does not represent substantial value for our customers money, so it has been decided to remove the reservoirs and dams and return the area back to their natural state. This may be back to a river valley or a smaller safer body of water like a pond or lake.
Dam removal is widely accepted as being beneficial for the environment. Our Environmental Regulator Natural Resources Wales (NRW) is supportive of the work we are doing, and we have worked closely with them through the discontinuance process. A conclusion from recent reports from Europe and the USA (Gough, et al, Dam Removal – A viable solution for the future of our European rivers, DRE2018) concluded that the removal of dams is the most cost-effective ecological restoration measure for rivers. Rivers respond rapidly after dam removal both in physical and ecological terms.
By discontinuing these structures, we will see an improvement in the local biodiversity of the area. Improved river connectivity is also important from a climate resilience perspective; allowing ecosystems and flora/fauna to move with climate change.
Detailed ecological surveys, assessments and mitigations have been undertaken by specialist environmental consultants to ensure the work does not cause a negative impact to the environment.
Although the dam structure is being removed, we will be returning the sites to their natural states as rivers / a natural lake. It is our intention that our work will enhance the beauty of local areas.
All reservoirs in Wales above 10,000m³ fall under the Reservoir Act 1975. This means there is a legal requirement to ensure dams are regularly inspected and maintained, to ensure their safety. This often involves substantial costs and there is always a residual risk associated with dams, particularly as assets age. Keeping them as they are when they are no longer needed to supply water for our network is therefore not a viable financial option for our customers.
Once the sites are returned to their natural state, they will continue to be places people can visit to enjoy. It also ensures that hazards such as deep water, and submerged draw off pipework is removed, so that previous dangers associated with illegal swimming are removed making it safer.
Each reservoir is unique, so a lot of consideration is undertaken to decide on the best option to return it back to its original state. The design and planning process is quite a long process, and the final solution is driven by the hydrology of the site (the way it will react to floods and storms when it is finished.) The design must be driven by that process.
As well as no longer being needed for water supply purposes, like all manmade structures, the dams are nearing the end of their operational lifetime. This means they would require significant investment to bring them up to modern day standards, as well as the ongoing operational running costs. This is not considered an effective use of our customers money. A recent study in the USA concluded that the removal of dams could be 10-30 times cheaper than their ongoing repair and maintenance (Grabowski, 2018), being a one-time investment that permanently restores natural stream functions and habitats.
The dams were primarily built to supply water to our customers. However, as the water networks have changed over the years many reservoirs have become redundant and no longer needed for their original purpose.
This is determined on a site-by-site basis but in general terms no. Reservoirs are manmade structures and therefore if a reservoir has fishing it will be because it is stocked with imported farmed fish. On removal of the Dam, it would not be viable to stock fish in a shallower pond and fishing will cease. Angling associations or fishing clubs will be consulted with throughout the initial stages, so they are aware.
Detailed flood modelling and assessments have been made and mitigation, where needed, put in place to ensure that discontinuance will not cause any increased flood risk. It is worth noting that discontinuance is removing the risk of dam flooding.
We have worked closely with NRW and environmental specialists to ensure our work does not damage the local environment. This has included for example, creating floating wetlands for water voles. Our work of removing a manmade structure will help to improve and enhance the local environment for the benefit of generations to come.
The removal of dams means improved connectivity to downstream watercourses, which is important from a climate change perspective allowing flora and fauna to move with climate change. Reservoirs that are no longer used for supply have been replaced by larger reservoirs and a change in how the water network is configured and supplied.