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.

Roath Park spillway

Questions and Answers

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?

The children’s play area was closed from Tuesday 16th – Friday 19th  November for the ground investigation works. For the future construction works we will look to keep the park open as much as possible, but there is likely to be some closure works are happening on that side of park to keep park users safe. Most construction work will be the other side of the park where the spillway is located.

When is the maintenance work due to start and what is it likely to entail?

Ground Investigation works are likely to start in November 2021, where investigations will determine the scope of the project and construction itself. Following community engagement, design and subject to planning determination, construction will begin Nov 2022 and last until late 2023.

How long will the work take?

Ground Investigation works will take up to around a month in November. The works are scheduled to begin Nov 2022 and last until late 2023.

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?

Ground investigation works will take place between Monday and Friday.  There will be no work at the weekend. During construction works, the operation days will be decided when a contractor is appointed.

Will the lake/reservoir be dredged for the main works?

We are currently looking into options for dredging the lake. Because the construction works may involve lowering the water level of the lake, this could provide a good opportunity to de-silt the lake.  As part of the current studies, samples have been taken to determine where the silt could be placed should it be removed.

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.

Which parts of the lake and park will undergo maintenance and be closed during construction?

The spillway will be the main focus of the maintenance works and there will be some works to the dam itself. We will aim to keep disruption to a minimum. More details will be provided once the design is finalised and a contractor is appointed.

Will the works affect Roath Park lighthouse?

No construction works are planned in the vicinity of the lighthouse. Construction will focus on the dam crest, dam slope into the park and the spillway.

There is the possibility that desilting works may be undertaken in the vicinity, but those works would only be to remove silt that has accumulated since the last time the reservoir was dredged.

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 for the ground investigation works. There may be a need to lock the gates temporarily overnight, and so we will provide specifics when available.

Will there be lasting effects on the surrounding biodiversity?

The design will seek to reduce the permanent disruption to the park to a minimum.

Temporary works to excavate and any construction works to the spillway may affect surrounding biodiversity, however every effort will be made to reinstate the existing features of the park on completion, as far as practicable.

What are the impacts 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, Natural Resources Wales have queried the inclusion of an eel pass within the spillway. It is likely there will need to be a small amount of tree felling but re-planting will take place.

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

There is no intention to change the current water level or capacity of the reservoir. 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 before, during and after the project for health and safety purposes and for environmental safety/pollution management.

Will the landscape change as a result of the works?

The intention is to make minimal changes to the landscape.

Will any trees be removed for the work to be carried out?

Yes. It is likely that some trees will need to be removed in the area to the left of the spillway (looking downstream), close to the Scott Memorial Garden, to facilitate the spillway rebuild.  We will seek to replace any trees that are felled.

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 upcoming ground investigation works, along with physical and computer modelling, will confirm the required size of the spillway.

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 back to front?

No strengthening works are needed to the dam. Some protective works are needed to the downstream face to make sure flood doesn’t erode that face, but the intention is not to make the dam wider or change its overall shape.

How will negative impact of amenity value be assessed? Will there be a full assessment?

Yes, an assessment and mitigation will be looked at and implemented to make sure there is no long-term detriment.

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

A Community Newsletter highlighting the improvements to the Roath Park Dam structure was issued on 24th September 2021 to stakeholders and the core consultation zone.


The project team also held a series of community information events about the project, which included an online Zoom webinar and two onsite drop-in events.


You can find further information on these here:

PowerPoint Presentation


As the project progresses we will continue to engage with stakeholders and local communities and are planning to host further information events in 2022.

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

Feedback on the project is welcomed via or Freepost GRASSHOPPER CONSULT . Regular updates on the project, any changes to access due to the ground investigations, and further works will be issued on Cardiff Council’s social media channels and the Outdoor Cardiff 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 member of Parliament, Senedd Members and ward councillors.

Press releases, 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.

Can we be consulted on options?

Options are being developed now and we can release when they are ready for comment.

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.

Following the flooding in Feb 2020, the wild gardens were underwater and the Roath Brook was full. Will this area be looked at?

The project focus is on the spillway and the dam itself, and small flood events in this area are not part of the remit.

How will additional flood risk be mitigated/assessed and against what criteria?

We’re exploring options for the spillway design to see if benefits can be provided to areas downstream and are in consultation with Natural Resources Wales.

What will be the impact on flooding downstream by Waterloo Gardens?

We are looking to introduce a 2 stage weir within the spillway with the aim of mimicking the existing flows or, if possible, making some improvements for certain flood events by utilising attenuation in the lake.

Are the houses along Roath Park at risk of flooding?

The risk should not change as a result of the works.

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

Llanishen and Lisvane reservoirs are non-impounding reservoirs and will not be affect 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 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 maintenance work 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 the Roath Park Reservoir 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

Roath park

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