Section 19 report, Flood and Water Management Act 2010 – Treorchy

The Council has today published its tenth report under Section 19 of the Flood and Water Management Act 2010, following the unprecedented weather of Storm Dennis. The latest report focuses on the causes of flooding in Treorchy. 

The Lead Local Flood Authority, under the Flood and Water Management Act 2010, must provide a factual account of what happened in significant flood events. The Council will provide a total of 19 reports for locations affected by Storm Dennis (February 15-16, 2020), following initial investigation of 28 areas.

Today’s publication follows reports covering Hirwaun, Nantgarw, Pontypridd, Treforest, Glyntaff and Taffs Well last month. Previous reports focused on Pentre (July 2021), Cilfynydd (September 2021) and Treherbert (November 2021), as well as an Overview Report for all of Rhondda Cynon Taf (July 2021). All of the reports are available to view in full on the Council’s website.

The reports identify Risk Management Authorities (RMAs), note the functions exercised so far, and outline what each RMA proposes to do in the future. They are informed by inspections made by the Flood Risk Management Team after the storm – as well as information collated from residents, the Council’s Public Health Team, Natural Resources Wales and Dwr Cymru Welsh Water.

The latest report, published on Thursday, February 24, focuses on Treorchy in the Rhondda Fawr valley (Flood Investigation Area 26). It notes that Storm Dennis resulted in 44 properties flooding internally, including four commercial properties and flooding to the highway. Rhondda Cynon Taf Council is identified as the Lead Local Flood Authority and the Land Drainage Authority.

The report is available to view in full on the Council’s website, here.

It establishes that the primary source of flooding was as a result of significant overland runoff being generated from the steep hillsides above Treorchy. This drained to lower ground via a series of ordinary watercourses, many of which became overwhelmed with water and debris, and eventually overtopped.

The condition and hydraulic performance of four culvert inlets identified as sources of flooding to properties were assessed. Three inlets associated to the Nant Tyle-du network do not provide adequate standards of protection. While blockages cause by debris is determined as the primary cause of the culverts surcharging, the report says they would have become hydraulically overloaded in the storm in any case, based on a capacity assessment.

An assessment for a fourth inlet, associated with the Nant Coly watercourse, could not be undertaken – however, based on the structure’s poor condition it is considered that the inlet became hydraulically overloaded in the storm.

The Council, as Lead Local Flood Authority, has undertaken 15 actions in response to the flooding, and has proposed to undertake a further three. These include clearance work carried out to the culvert inlet structures identified as sources of flooding – along with survey work, cleansing and jetting of 1,673 metres of ordinary watercourse within the investigation area.

The Council has led on the development of an Emergency Control Room, bringing together its Call Centre and CCTV operations to provide a multi-agency, comprehensive and informed response during future storm events.

It has also started an interim Property Flood Resistance project which offers expandable flood gates to those properties deemed at high risk of ordinary watercourse and surface water flooding – while remote telemetry monitoring devices have been installed at key structures in the Treorchy area.

The Council will look to better understand the catchment around Treorchy by developing an Outline Business Case to provide recommendations for suitable management mechanisms. This will aim to mitigate the future risk of ordinary watercourse, surface water and groundwater flooding locally.

Following the progress completed to date, the Lead Local Flood Authority has completed a supporting Business Justification case with its associated detailed design – to support the delivery of Phase 1 of the wider Outline Business Case, with commencement programmed for early spring.

The report concluded that the weather of Storm Dennis was extreme, and it is unlikely that flooding could be prevented entirely if a similar event was to occur. It concludes that the Lead Local Flood Authority satisfactorily carried out its functions in response to the flooding, with further measures proposed to better address preparedness and response in future flood events.

Councillor Andrew Morgan, Leader of Rhondda Cynon Taf Council and Cabinet Member with responsibility for Highways and Transportation, said: “The Council has now published its tenth Section 19 report, which is required following the flooding during Storm Dennis. This report for Treorchy is the seventh since the New Year, following those focusing on Hirwaun, Nantgarw, Pontypridd, Treforest, Glyntaff and Taffs Well in recent weeks.

“Investigating what happened in Storm Dennis remains a priority for the Council, to ensure we are best prepared for any future storm events and for the consequences of Climate Change. On the recent two-year anniversary of the storm, the Council published a detailed update on the ongoing activity in our communities to deliver flood alleviation schemes, and to repair and improve key infrastructure such as bridges, walls and culverts.

“Since Storm Dennis, more than 4,000 reports of flooding have been investigated, 60km of watercourse have been inspected, and more than 2,500 tonnes of debris have been removed from this infrastructure. An accelerated capital programme of more than 100 flood alleviation schemes is being delivered, with the investment at £13m by the end of the current financial year.

“Today’s Section 19 report on Treorchy identified the cause of flooding, and outlines the actions of the Council as the Lead Local Flood Authority. It concludes that this Authority undertook its duties in a satisfactory way, and puts forward measures proposed to increased preparedness for any future flood event. The report is fully-accessible on the Council’s website.”

Posted on 24/02/2022
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