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Culverts in Cwmbach provided “inadequate standards of protection” during Storm Dennis 2020,

SOME culverts in Cwmbach provided “inadequate standards of protection” during the floods caused by Storm Dennis, a council report has revealed. The extreme rainfall during the storm saw internal flooding to 34 properties, including 18 commercial properties.

The latest section 19 report from Rhondda Cynon Taf Council looking into the causes of flooding during February 2020 said that, from the evidence gathered, the primary source of flooding was as a result of significant overland runoff being generated from the steep hillsides above the village. The rainwater then drained to lower ground via a series of ordinary watercourses – many of which became overwhelmed with water and debris, and eventually overtopped.

It added that the remaining three culvert networks identified as sources of flooding provided adequate protection in free-flowing conditions but despite having enough capacity to manage expected flows, the infrastructure was seen to be in a poor condition and their capacities were “significantly reduced” by debris blockages.

The report said the main source of flooding was as a result of significant overland water run-off from the steep hillsides above the village.

It added that the rainwater then drained to lower ground through a series of ordinary watercourses – many of which became overwhelmed with water and debris and overflowed, affecting several properties.

The report concluded Storm Dennis was an extreme event and it is unlikely flooding from a similar event could be prevented entirely.

It added that the relevant authorities satisfactorily carried out their functions in response to the flooding, but further measures to improve preparedness have been proposed by them all.

The council as lead local flood authority and land drainage authority is responsible for managing ordinary watercourse and surface water flooding.

Some of the completed actions have included clearance of culvert inlet structures and survey work, cleansing and jetting to 2,413m of culverted watercourse and highway infrastructure in the local area.

The report said the council has also led on the development of a multi-agency control room, linked to its contact centre, to ensure a coordinated response in future flood events – and has started an interim property flood resistance project offering expandable flood gates to properties deemed at high risk of flooding.

The report said the council will also look to better understand the catchment above Cwmbach and explore recommendations on how to mitigate the wider risk of ordinary watercourse, surface water and groundwater flooding locally.

Natural Resources Wales (NRW) is responsible for managing the river flooding in Cwmbach and has commissioned a Cynon flood modelling study. The outcomes will include an assessment of the potential flood risk management options.

The report said NRW has also carried out a waterway clearance of the ‘Cwmbach Ditch’ which was identified as a source of flooding to one property.

It has also developed recommendations and a detailed action plan to address improvement areas for future storm events, including the performance of the NRW Flood Warning Service Review and incident management response.

Roger Waters, Rhondda Cynon Taf Council Director, Frontline Services,said:

“The Council has now published 13 flood investigation reports following Storm Dennis, which is a requirement of the Lead Local Flood Authority under Section 19 of the Flood and Water Management Act 2010. Each report identifies Risk Management Authorities and notes their actions since the flood event – as well as the actions that they propose to undertake in the future.

“Each report is a factual document which is fully-accessible for members of the public, published on the Council’s website. Officers continue to work towards publishing 19 reports in total, focusing on specific communities – with the final six being progressed. The latest publication in relation to Cwmbach has concluded that all RMAs undertook their responsibilities in a satisfactory way, and have put forward further measures to improve future preparedness.”


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