The Rhondda Fawr village of Pentre was hit by flooding on five separate occasions in 2020
Section 19 report statement from Rhondda Cynon Taf Council
The Rhondda Fawr village of Pentre was hit by flooding on five separate occasions in 2020. Section 19 of the Flood and Water Management Act 2010 requires the Lead Local Flood Authority, in this case the Council, to provide a factual account of what happened. It focuses on the initial flood event during Storm Dennis (February 15-16), but also takes into consideration the four events that followed, identifying the mechanism for flooding, identifying the Risk Management Authority responsible for managing the risks, and assessing the actions of the Risk Management Authorities identified.
Unprecedented rainfall in Storm Dennis caused record river levels and flows, as Rhondda Cynon Taf recorded its most significant flooding since the 1970s. In total, 159 residential properties and 10 commercial properties were flooded in the village of Pentre alone, along with significant flooding to local highways.
In the days following Storm Dennis, the significant impacts were identified via inspections by the Council’s Flood Risk Management team, and information and accounts collected from residents, the Council’s Public Health team, Natural Resources Wales (NRW) and Dŵr Cymru Welsh Water (DCWW).
The Section 19 report states that the main source of flooding in the initial flood was due to a significant blockage by woody materials including brash, at the Pentre Road culvert inlet. It resulted in water flowing down Pentre Road, onto Elizabeth Street and Queen Street, and towards the lower streets of the village.
It reports that the culvert inlet, within the ownership of Welsh Government Woodland Estates and managed by NRW, was blocked by woody debris washed off the mountainside, including an area where tree felling activity had been undertaken by NRW. This severely reduced the hydraulic capacity of the inlet.
A review of the inlet itself identified that it had sufficient capacity to deal with the storm event if there was no blockage. This also resulted in a significant amount of woody debris washing into the culvert network, contributing to repeat flooding in the lower reaches of Pentre in subsequent storms. Mud and silt entered the highway drainage infrastructure, which substantially reduced its capacity too.
The full report can be found on the Council's website by clicking here.
Councillor Andrew Morgan, Leader of Rhondda Cynon Taf Council, said:“The publication of this Section 19 report considered the factors which contributed to the severe flooding experienced in Pentre in February 2020, following a detailed process of evaluation and collation of evidence. The robust process has included significant engagement with residents and businesses impacted, and an analysis of data relating to this flooding event and has now determined the underlying causes which contributed towards the specific flooding events during Storm Dennis.
“It is evident that blockage of the culvert inlet by woody material severely impacted upon the ability of the drainage infrastructure to manage this unprecedented level of rainfall. Despite the severe nature of Storm Dennis, technical assessment confirms that without this debris the culvert inlet would have provided sufficient capacity to manage the exceptional amount of water running from the mountain. Had the water been able to enter the culvert, the culvert would have significantly reduced the impact any flooding would have had upon the local community. The Council is of the view that this evidence is irrefutable.
“As a Council we recognise that Natural Resources Wales has managed the land above the culvert and note their assertion that tree felling at this location was undertaken in-line with national best practice. Whilst the Council’s report does not comment on their land management practices, we do conclude that the primary cause of flooding was as a result of a blockage to the inlet with the significant contribution to the blockage being the presence of woody debris.
“The Section 19 report rightly states that the weather in Storm Dennis was extreme and it is unlikely that flooding from a similar event could be prevented entirely. It importantly concludes that the Risk Management Authorities (the Council) satisfactorily carried out their functions in response.
“Within this report, as the Local Flood Management Authority, the Council, proposes a number of actions to reduce the risk of an occurrence such as this happening again.”
The Council, as Lead Local Flood Authority and Land Drainage Authority, is the relevant Risk Management Authority responsible for managing the ordinary watercourse flooding that occurred in Storm Dennis. It is working closely with NRW and DCWW to assess the risk of future flooding in Pentre and develop a range of flood alleviation options. So far, it:
- Has carried out significant upgrades to the Pentre Road inlet to reduce potential blockages, with multiple overflow systems at the culvert should there ever be a future blockage to the main grill.
- Has installed a monitored alarm system and CCTV at the culvert inlet to remotely alert the council of any problems 24/7.
- Has developed and implemented a “super catchpit” capable of containing 6Ton of debris at Pleasant St to alleviate the risk of debris transportation to the flatter lower parts of the culvert system.
- Is developing proposals for a flood routing scheme at Pleasant St.
- Has worked with DCWW to construct a high-level overflow to increase the capacity of the highway drainage network in Lewis Street.
- Has begun developing proposals for significant efficiency upgrades to Volunteer Street pump station.
- Is leading on the development of an Outline Business Case for Pentre which seeks to mitigate flood risk in the community.
The Council has also made the following recommendations in respect of land management:
- To review NRW’s own Forest Resource Plans and Coupe Plans for water management, particularly surface water management and the treatment of brash material close to an ordinary watercourse.
- To develop a Forest Resource Plan for the Rhondda Fawr valley in collaboration with the Lead Local Flood Authority, to identify and reflect the key challenges facing the community of Pentre.
- To embed NRW’s own Water Management Plans into their forestry management operations to ensure the impacts of flood risk downstream are fully realised.
- To engage with residents in relation to Forest Resource Planning and forest operations to help develop greater confidence in the WGWE and NRW’s contribution to managing surface water runoff from their land.
