Roath Park Dam Improvement Works

A long list of potential solutions to deal with an extreme flood event was produced.

During an initial review, some options were discounted for not achieving the necessary dam safety benefits. On the right is a high-level summary of the discounted options.

Following review of the long list of options, a short list of the three technically viable options was explored in more detail. Concept sketches of these options are shown below.

This option is the replacement of the existing spillway with a much larger structure, which would require the removal of the Terra Nova café.

This option was discounted due to the significant disruption to the park and the loss of the café.

This option is the replacement of the existing spillway with a wider and deeper structure and the addition of a flood wall along the promenade.

This option has been taken forward as the preferred solution as it meets all dam safety requirements and results in least disruption to the park.

This option is the addition of a new spillway through the children’s playground. The existing spillway would remain untouched and the playground would be relocated elsewhere.

This option was discounted due to the significant disruption to the park and playground.

The preferred solution is Option B; to replace the existing spillway with a wider and deeper structure and to add a flood wall along the promenade.

Below are visualisations showing what the solution may look like once constructed. This design will need to be submitted for planning consent and so may be subject to change.

The existing weir is 19m long and this will be replaced with a 25m long weir with two levels. The spillway will become deeper and so the number of steps below the weir will increase. The bridge across the spillway will become wider. There will be a new wall in front of the Terra Nova café but the café itself will remain unchanged.

A new 1.1m high flood wall will be constructed along the southern side of the promenade. This matches the height of the existing railings. Benching and planters will be replaced along the centre of the promenade and will face the lake. The Terra Nova garden feature will be moved to another location in the park.

The Ranger’s Hut will be removed and new public seating will be created in the surrounding area adjacent to the weir and café. The park entrance gate and ice cream kiosk will remain unchanged.

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. An eel pass will run on one side of the spillway. A number of trees will be removed along eastern edge of spillway to facilitate its construction and will be replaced by low level planting, which will allow better inspection and maintenance of the spillway.

In the event of tree loss, 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.

The pooled steps down the existing spillway will be included in the new design. There will be no changes to the downstream bridge or the channel past this point.

The railings along the southern side of the promenade will be changed to a new 1.1m high flood wall (the same height as the existing railings). There will be no works undertaken to the southern dam slope or the large oak tree at bottom of dam. There will be some disruption to the playground during construction.

The size and dimensions of the new spillway and flood wall are determined by engineering requirements.

As the existing spillway is a Grade II Listed Structure, it will be necessary to ensure its replacement is sympathetic to the original. As much as possible, the original stone will be reused and where necessary, additional matching stone will be sourced. The new spillway will be constructed with concrete walls and base, and lined with dressed stone.

As Roath Park is designated as a Historic Park and Garden, the new flood wall will need to be sympathetic to its surroundings within a heritage park.

For structural stability, the interior of the wall will be formed of concrete, and its exterior will be clad with materials that are characteristic of the local area. Here are some examples of existing walls in the neighbourhood.

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.

Mitigation measures will also be looked at as part of the design development; for example, an eel pass will be included within the spillway.

The plans to minimise any impact on the local community during the construction works will be set out by the contractor once they are appointed in 2023.

The site working times and traffic management will be agreed with the contractor prior to their appointment.

Various areas of the park near the dam will need to close during the works. All closures will be planned and communicated in advance to community stakeholders and local residents.

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.

For any further queries, please check the Questions & Answers section on our  webpage .