Two further Section 19 reports under the Flood and Water Management Act 2010 have been published following Storm Dennis – with the latest reports covering Aberdare and Aberaman, as well as Rhydyfelin and Hawthorn.
As the Lead Local Flood Authority, Rhondda Cynon Taf Council must provide a factual account of what happened during any significant flood events. Under the 2010 Act, the Council will publish a total of 19 reports focusing on specific communities following the unprecedented weather of Storm Dennis (February 15-16, 2020). They follow initial investigation of 28 areas that were affected.
So far in 2022, reports have been published for Abercwmboi/Fernhill, Porth, Taffs Well, Glyntaff, Treforest, Pontypridd, Nantgarw, Hirwaun, Treorchy, Ynyshir, Trehafod and Cwmbach. Reports published in 2021 focused on Pentre, Cilfynydd and Treherbert, as well as an Overview Report covering the whole of Rhondda Cynon Taf. All reports are available to view in full online.
Section 19 reports identify the Risk Management Authorities (RMAs), note the functions that they have exercised, and outline what actions they propose to take in the future. They have been informed by inspections and data collection carried out by the Council’s Flood Risk Management Team after the storm – as well as information collated from local residents, the Public Health Team, Natural Resources Wales (NRW) and Dwr Cymru Welsh Water (DCWW).
The publications on Thursday, July 28, focus on Aberdare and Aberaman in the Cynon Valley (Flood Investigation Area RCT 02), and Rhydyfelin and Hawthorn in the Taf Valley (Flood Investigation Area RCT 15) respectively.
Both reports are available to view in full on the Council’s website, here.
Aberdare and Aberaman (Flood Investigation Area RCT 02)
The report states that 45 residential properties and five commercial premises flooded, while there was also highway flooding. The main cause of flooding is identified as significant overland runoff being generated from the steep hillsides above Aberdare and Aberaman, draining to lower ground via a series of watercourses – many of which became overwhelmed with water and debris.
Upon a review of the condition and hydraulic performance of the culverted infrastructure, it was found that two networks provided inadequate standards of protection in free-flowing and blocked conditions. The remaining networks were found to have adequate protection in free-flowing conditions. The Nant Gwawr culvert had sufficient capacity to manage flows, but was observed to be obstructed by blockages due to mobilised debris from upstream.
The overtopping of the River Cynon was also identified as a primary source of flooding to properties at Wellington Street in Trecynon, and also influenced the overtopping of the ordinary watercourse behind Gloucester Street. Unprecedentedly high river levels contributed to the severity of the overtopping at this location – with NRW’s Aberdare station recording its highest peak level of 2.125-metres.
Surface water flooding associated to sheeting runoff from the hillsides, and an overwhelmed highway drainage network, were also identified as contributing sources of flooding to several properties within Aberdare and Aberaman.
As the Lead Local Flood Authority, Land Drainage Authority and Highway Authority, the Council has undertaken 16 actions and proposed a further 11. It has undertaken significant clearance work to the structures identified as a source of flooding, carried out survey, jetting and cleansing to 921m of culverted ordinary watercourse network, and led on the development of a central control room to provide a comprehensive, multi-agency response during future storm events.
The Council has also carried out significant upgrades to the culvert inlet structures and ordinary watercourse networks to reduce the risk of blockages, and installed remote telemetry monitoring devices at key culvert structures.
As the RMA for main river flooding, NRW has carried out its own post-event analysis to understand the mechanism of flooding from the River Cynon at Aberdare, and commissioned a Cynon Flood Modelling Project to assess the viability of potential flood risk management options. It has also developed an action plan to address areas of improvement, including the performance and expansion of its Flood Warning Service and incident management response.
Rhydyfelin and Hawthorn (Flood Investigation Area RCT 15)
The report notes that 28 residential properties were flooded, along with five commercial properties and extensive flooding to the highway. The primary source was as a result of significant overland runoff being generated from the steep hillsides above Rhydyfelin, draining to lower ground via a series of watercourses – many of which became overwhelmed with water and debris.
All three culvert inlets identified as sources of flooding became overwhelmed with debris, which caused a reduction in their hydraulic capacity. The Nant Lonydd ordinary watercourse also overtopped at several locations, and was a primary source of flooding – heavily influenced by the high levels of the River Taff which caused a backup of flow upstream. NRW mapping identifies that there are currently no formal flood defences in place at this location.
As the Lead Local Flood Authority, Land Drainage Authority and Highway Authority, the Council has undertaken 15 actions and proposed a further nine. It has undertaken clearance work to the structures identified as a source of flooding, carried out survey, jetting and cleansing to 1,539m of culverted ordinary watercourse network, and led on the development of a central control room to provide a comprehensive, multi-agency response during future storm events.
The Council has also undertaken repair works to the river retaining wall on unregistered land to the rear of Hawthorn Crescent, that was damaged during Storm Dennis. It is also working collaboratively with NRW to manage the flood risk caused by the influence of the River Taf on the Nant Lonydd watercourse.
Both reports concluded that Storm Dennis was an extreme event, and that it is unlikely flooding could be prevented entirely in a similar event. They add that all RMAs satisfactorily carried out their functions in response to the flooding, but have each proposed further functions to better prepare for future events.
Councillor Andrew Morgan OBE, Leader of Rhondda Cynon Taf Council and Cabinet Member for Infrastructure and Investment, said: “These latest Section 19 flood reports cover the areas of Aberdare, Aberaman, Rhydyfelin and Hawthorn – and follow the recent reports in June for the communities of Abercwmboi, Fernhill and Porth. In total, 17 of the 19 reports following Storm Dennis have now been published, since the first one during summer 2021.
“The reports’ purpose is to identify what happened in our communities during Storm Dennis – while identifying Risk Management Authorities, their actions to date, and their future proposals. The reports are based on evidence collected from key organisations and public eyewitness accounts. It is important to note that preparing the reports has not prevented important works from taking place in our communities as a priority – as our accelerated capital programme of more than 100 flood alleviation schemes continues to make good progress.
“More than £6.4m Welsh Government funding has been secured by the Council for Storm Dennis works in 2022/23, along with around £3.9m for flood alleviation across the Flood and Coastal Erosion Risk Management and Small Scale Works Grant programmes. In addition, £440,000 has been allocated to progress a further 10 Resilient Roads schemes throughout the year ahead.
“All of the published Section 19 reports are fully-accessible for members of the public, and are available on the Council’s website. These include the latest two reports covering Aberdare and Aberaman, and Rhydyfelin and Hawthorn.”
Posted on 28/07/2022