Blocked drainage system was main cause of Pentre flooding, investigation finds

An investigation into severe flooding in a south Wales village has found that a blocked drainage system was the main cause.

Pentre, near Treorchy in Rhondda Cynon Taf, was badly during Storm Dennis in February 2020.

Unprecedented rainfall caused record river levels, with Rhondda Cynon Taf recording 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.

As the lead local flood authority, Rhondda Cynon Taf council was required to investigate the contributing factors.

Its findings, published today, said the primary cause of flooding was due to a "significant blockage by woody materials" at a culvert inlet - a form of drainage - on Pentre Road.

The report states that the debris had washed off the mountainside, including an area where tree-felling activity had taken place.

This reduced the hydraulic capacity of the inlet and resulted in water flowing down Pentre Road, onto Elizabeth Street and Queen Street, and towards the lower streets of the village, it said.

A review of the inlet itself identified that it had "sufficient capacity" to deal with the storm if it hadn't been blocked.

Pentre residents spoke of their desperation at the repeated flooding.

Councillor Andrew Morgan, leader of Rhondda Cynon Taf Council, said: "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, it 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."

But Mr Morgan added: “The report rightly states that the weather in Storm Dennis was extreme and it is unlikely that flooding from a similar event could be preventedentirely."

The culvert falls within the ownership of Welsh Government Woodland Estates and is managed by Natural Resources Wales.

In a statement, a Natural Resources Wales spokesperson said: "We accept that woody material washed off the mountains above Pentre may have contributed to blockages to the culvert system, which also included a significant amount of soil and rock.

"However, a proportion of the woody debris was unrelated to NRW’s felling operations and was washed down as a natural consequence of such an extreme event. NRW therefore disagrees with the report’s inference that its harvesting operations were theprimary cause of the flooding during Storm Dennis."

Natural Resources Wales' own review into the floods found that the tree-felling methods "were appropriate and in line with forestry standards, and that these operations were not likely to have been the primary cause of the flooding".

The spokesperson added: "We have to accept that we cannot stop the rain and that some flooding is inevitable. Climate change is leading to more extreme weather events, and we are certain to see more of the types of storms we saw in 2020 in the future."

The organisation said its thoughts remain with the residents affected.

Storm Dennis caused flooding in parts of Wales - pictured here is Nantgarw, Rhondda Cynon Taf. Credit: PA Images

Julie James MS, minister for climate change, said: “I welcome this report, there are some concerning findings and clearly lessons need to be learned following the devastating floods last year. Both Natural Resources Wales and Rhondda Cynon Taf Council have acknowledged this in their respective reports.

“We now want all flood Risk Management Authorities to work together to develop a plan of action for the Pentre community to provide clarity on the action they have taken since 2020, the plans for future action to tackle flood risk in the area and the action to be taken in the interim to support the community.

“I will also be asking them to take whatever action is necessary to prepare for this coming autumn and winter.”

Pentre was hit by severe flooding on five separate occasions in 2020.

Upgrades have since been carried out in the area and the council has made a number of land management recommendations to reduce the risk of further flooding.