Roath Park Dam Project

Developing options for future effectiveness

Roath Park Lake is a manmade reservoir, formed by a dam structure to the south and fed by the Nant Fawr. Cardiff Council is legally responsible for maintaining the publicly owned Roath Park Dam, and routine inspections are required under the Reservoirs Act (1975).

The latest inspection of the reservoir found that the dam’s spillway capacity would not be large enough to withstand a theoretical extreme flooding event and statutory works are now required.

Developing our proposals

Arup, a leading engineering consultancy, has been appointed to undertake a study to explore the best options to ensure the future effectiveness of the dam and make sure one of Cardiff’s most treasured parks can be enjoyed safely by future generations.

Arup has now completed the detailed study which has assessed a range of options to address the spillway capacity and have now identified a preferred solution.

Project update

Last year we completed our ground investigation works at the dam which were undertaken in order to inform plans to improve the safety of the dam.

We are committed to working with the local community to ensure they understand the work involved. We’re now holding the next phase of public engagement to share the progress we have made in the developing the project and to give you an opportunity to give your feedback on the proposals.

View the project proposal website

Questions and Answers

Updated November 2022.

Who is responsible for maintaining Roath Park Dam?

Cardiff Council is legally responsible for maintaining the publicly owned Roath Park Dam, and routine inspections are required under the Reservoirs Act (1975).

Will the park have to close?

Various areas of the park near the dam will need to close during the ground investigation works and construction phases. All closures will be planned and communicated in advance to community stakeholders and local residents.  There will be regular updates on Cardiff Council’s social media channels. If changes arise due to unforeseen circumstances, these changes will be communicated as early as possible.

Will the children’s play area be closed?

For the construction works we will look to keep the park open as much as possible, but there are likely to be some closures of the play area to keep park users safe.

When are the improvement works due to start?

We are currently developing the design of the improvement works and are engaging with the community regarding this design in December 2022. In 2023 we shall share the final proposals prior to submitting the planning application. Subject to planning permission, the construction will begin in 2024.

How long will the work take?

Subject to planning permission, the works are scheduled to begin in 2024 and expected to last 12-15 months.

Is the timeline correct?

The timeline is provisional and subject to design being completed and the planning application being approved. This is the best estimate currently, but it is subject to change.

What will be the working hours during the construction works?

The site working days and hours will be decided when a contractor is appointed.

What will happen to the water in the lake during construction?

It is likely that lake will be drained to make it safer, easier and quicker to access the spillway. No timescale for this is currently available.

How will water outflow be managed during construction?

The water outflow is managed via pipes which run through the base of the dam, called ‘scour pipes’.  There may need to be some pumping to aid this.

Will the works affect Roath Park lighthouse?

No construction works are planned in the vicinity of the lighthouse. Construction will focus on the promenade and the spillway.

Will either Lake Road West or Lake Road East need to close for the works to take place?

At this stage, we do not anticipate needing to close either Lake Road West or Lake Road East.

Will either Lake Road West or Lake Road East require traffic management while the works take place?

It is likely that traffic management will be required at times. With construction traffic and delivery vehicles needing to enter and exit the park, traffic management may be necessary to ensure the safety of park users, the public and construction staff.

Will the park be locked at night?

Working areas will be fenced off as part of security. There may be a need to lock the gates temporarily overnight, and if so we will provide specifics when available.

What could the impacts be on local wildlife and trees?

Impacts on local wildlife and trees will be kept as minimal as possible. Some surveys have already been undertaken by ecologists and further surveys will be carried out as the scheme progresses and throughout construction. An environmental management plan will be developed by the contractor for the construction phase. Mitigation measures will also be looked at as part of the design development; for example, an eel pass will be included within the spillway. It is likely some trees will need to be removed. In the event of any tree losses, replacement planting numbers in the local area will exceed the number lost. It may not be possible to re-plant trees in their original location due to the increase in the spillway footprint and dam safety requirements.

Will the works mean the height of the water in the lake is increased?

There is no intention to change the current water level or capacity of the lake. The water level is set by the weir. Long dry periods will make it drop, heavy rain and storms will make it rise.

Will the water quality be tested for health and safety?

Water testing will be done during construction for health and safety purposes and for environmental safety and pollution management.

Will the landscape change as a result of the works?

The intention is to make minimal changes to the landscape.

Will there be any enhancements to local biodiversity?

Mitigation will be provided for any disturbed important biodiversity.
Potential enhancements have not yet been discussed.

What width and length will the replacement spillway be?

The existing spillway is 6m wide by up to 3m deep and this will be replaced by a larger structure, approximately 8m wide by up to 6m deep.

Will the height of the dam be increased?

We are not intending to raise the height of the dam.

Will the dam be made wider?

We are not intending to make the dam wider or change its overall shape.

How and when are stakeholders and local communities going to be engaged?

A community newsletter highlighting the improvements to Roath Park Dam was issued on 24 November 2022 to stakeholders and the core consultation zone.

If you have any queries or require further information about the project, please contact the project team by telephone, 02920 130 061, or email

How will the community and stakeholders be given feedback and kept informed of the project’s progress?

Further works will be issued on Cardiff Council’s social media channels and this website, as well as issuing newsletter updates to those who live close to the site.

Who is being consulted about the project?

We have undertaken an extensive stakeholder mapping exercise identifying key stakeholders in the community who should be engaged.

A core consultation zone has been defined with includes 4831 households and 59 businesses in street around Roath Park and the recreation ground.

Grasshopper Communications is leading regional and local stakeholder engagement including the following sectors: heritage, recreation and outdoors, faith, public services, utilities and infrastructure, environment and sustainability, tourism and economic development, further education and university, transport, local businesses, community facilities, schools, community groups and equalities.

Cardiff Council is leading on political stakeholder engagement including Members of Parliament, Senedd Members and ward councillors.

Press releases, a social media campaign and posters in the park will be used to inform the wider community of Cardiff and beyond.

How will the community and stakeholders’ views be considered?

We welcome feedback on the project and will seek to address issues that arise. Feedback submissions will be considered before submitting the planning permission.

Will you be maintaining the edge of the lake as part of the work?

This is not in the remit of the project. If you wish to discuss maintenance of the park please contact the park wardens office.

Will the stone sides of the brook south of the spillway be maintained as part of the works?

Repairs may be made around the bottom end of the spillway towards the natural watercourse. Anything further downstream of this point is outside the remit of this scheme.

Will the works involve dredging further downstream by Waterloo Gardens?

There are no plans to do this as part of this scheme.

Will work be carried out upstream of the lake or just on the spillway?

Opportunities to attenuate flows upstream have not proven to be suitable and are not being taken forward.

Will flood risk in the area be affected by the proposed works?

The primary aim of the scheme is to make the necessary improvements to ensure extreme flood events can safely pass the dam. It focuses on the safety of the dam and the downstream population, and the scope is not to reduce downstream flood risk.

As part of the planning application, it will be necessary to produce a Flood Consequence Assessment (FCA). As part of the FCA application process, we will need to demonstrate that any effects on downstream flooding as a result of the dam improvement works are manageable. The design is being developed in accordance with TAN15 requirements, which is the Welsh Government’s technical advice note for development and flood risk.

What are the impacts on the upstream reservoirs (i.e. Llanishen and Lisvane)?

Llanishen and Lisvane reservoirs are non-impounding reservoirs and will not be affected by the works.


What are the long-term impacts of climate change in the area?

Climate change will have a significant impact on flooding in Wales. Storms are likely to be more frequent and of higher intensity, which would result in the dam spillway needing to safely pass an extreme flood event.

Is the dam structurally safe?

Yes, there are no concerns over the stability of the dam.

Where is the source of the Nant Fawr Brook and where does it end?

The Nant Fawr Brook begins just north of the M4 above Cardiff and flows into the Roath Brook, then into the Rhymney River, before flowing into the Severn Estuary.

What is the Reservoirs Act (1975)?

Reservoirs in England and Wales are regulated under the Reservoirs Act (1975), enforced by Natural Resources Wales in Wales. The Act exists to protect public safety by reducing the risk of an uncontrolled release of water from large, raised reservoirs and the dangerous flooding this can cause.

Why do we need to manage flood risk and dam safety?

Roath Park is a well-used public place. Undertaking improvement works ensures the safety of the dam and reduces the risk of flooding from an uncontrolled breach. It will ensure the future effectiveness of the dam, thus protecting lives and livelihoods, and making sure one of Cardiff’s most treasured parks can be enjoyed safely by future generations.

Who is responsible for managing the safety of the dam?

Cardiff Council is responsible for the dam’s maintenance and is required to undertake regular inspections of the dam and its spillway (under the Reservoirs Act 1975).

What will happen if the improvement works to the dam are not undertaken?

The purpose of the works is to improve the safe passage of flood water through the reservoir and prevent an uncontrolled release of water that could endanger those downstream. If works are not undertaken, in an extreme flood event there could be damage to the dam that causes release of the retained lake and significant increased flooding of areas downstream.

Was Roath Park Lake designed to be used for water consumption?

The reservoir was built for amenity, not for water supply, and has never been extracted for potable supply.

Keeping in touch

If you have any queries or require further information about the project, please contact the project team by telephone, 02920 130 061, or email

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