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Cowbridge, Wales


Redevelopment of the dilapidated former Royal British legion Club in Cowbridge was proposed in 2008 to provide much needed residential accommodation in the town centre. As the proposed development site was situated adjacent to the River Thaw in Cowbridge, it was designated as a floodplain and so in accordance with TAN15 it was initially recommended that residential development should not be considered.

At the time of the proposed development, the Environment Agency had recently completed a storage flood defence scheme for the River Thaw, installed upstream from the proposed development site. The scheme consisted of an embankment with a flow control structure that would limit the flow in the river to a very small amount, whilst diverting flood waters to the Thaw floodplain upstream. The scheme was designed to protect the town against a 1 in 100 year flood event.

When looking at the proposed development the Environment Agency specified that the design must be based on worst case pessimistic conditions, where the existing defences overtop and the culvert on the High Street is partially blocked. It was decided that a clever and robust flood mitigation solution based on these levels should be achieved and agreed by all parties. Following negotiations regarding this initial objection, an amended Flood Consequence Assessment was submitted in 2009.

All parties required a mitigation solution to be adopted that would include rainwater harvesting and on site run off control. It was also imperative that the development would not cause any material additional impact on downstream areas.


The amended plans deleted any enclosures separating the rear garden areas and potential blocking flood waters, and included the provision of a void beneath the proposed dwellings with a barrier system allowing the void to flood in the event of any severe flooding. 

Undercroft flood storage of 3,500 cubic metres would be installed controlled by a specialist system designed by our specialist technical staff that would drop automatically to divert flood water into storage. This would be linked to the Environment Agency’s own telemetry monitoring system.

A Section 106 was agreed which included planning obligations to ensure the future maintenance of this system and to restrict occupiers from using the void for storage. This agreement gave unrestricted access to the Environment Agency for maintenance purposes. The flood mitigation measures ensured that the challenges usually encountered with stilted development were not realised with this site.

TAN15 requires that the risk of flooding at any proposed development is acceptable and appropriate to the scale and nature of the proposed development and that the consequences of flooding for the development are manageable to an acceptable level. As all of these stipulations were met by the design and no flood risk to other areas in the catchment could be evidenced, the development met the requirements of the TAN15 planning policy.

Environment Agency Wales were re-consulted on the amended FCA and plans on 11 August 2009.  Their response received on 20 August 2009 stated:

”We have considered the new FCA above produced by MDC Limited, dated August 2009.  We recognise and welcome that our previous advice has been taken on board and reflected in the above submissions to us. Based upon the information contained within this report we would raise no objection to this development from a flood risk perspective.”