Section 19 Flood Investigation Reports for three further areas
Written by Gavin on 25th January 2022
Rhondda Cynon Taf Council has published three more Section 19 Flood Investigation Reports following Storm Dennis – focusing on investigating the flooding that occurred in Treforest, Glyntaff and Hawthorn, and Taff’s Well respectively.
The Flood and Water Management Act 2010 (Section 19) requires the Lead Local Flood Authority – in this case, Rhondda Cynon Taf Council – to provide a factual account of what happened during major flooding events. They must identify the Risk Management Authorities (RMAs), and report on the functions each has exercised to date and what functions they propose to exercise.
Following its investigation into 28 locations affected by Storm Dennis during February 15-16, 2020, the Council will produce 19 reports in total. It has previously published an Overview Report for all of Rhondda Cynon Taf (July 2021), and further Section 19 reports focusing on the communities of Pentre (July 2021), Cilfynydd (September 2021) and Treherbert (November 2021).
The latest reports – published separately on Tuesday, January 25 – focus on the communities of Treforest, Glyntaff and Hawthorn, and Taff’s Well. Each report was informed by RCT Flood Risk Management Team inspections in the days after Storm Dennis, as well as information from residents, RCT Public Health Team, Natural Resources Wales (NRW) and Dwr Cymru Welsh Water and consultant led technical reports.
Treforest (Flood Investigation Area RCT 12)
Storm Dennis resulted in flooding to 50 properties in the area, including 43 houses, along with significant highway flooding. The report establishes the primary source of flooding in Treforest as the overtopping of the River Taf following persistent and heavy rain. NRW’s river level gauge recorded the river to be almost four times higher than it usually would be, peaking at 5.32m.
Using NRW mapping, the impacted properties are identified as ‘medium and low risk’ of flooding from the river. Normal defences were in place but were overtopped in Storm Dennis. The investigation also identified that surface water accumulation on the highway contributed to the flooding and exacerbated existing fluvial flooding.
Glyntaff and Hawthorn (Flood Investigation Area RCT 14)
In total, 27 properties (including 23 houses) flooded, along with significant highway flooding. The primary source of this in Glyntaff and Hawthorn was the overtopping of the River Taf at several locations along its eastern and western embankments, after persistent and heavy rain. NRW’s gauge recorded the river level to be almost four times higher than usual, also peaking at 5.32m.
NRW mapping identifies the impacted properties as ‘high risk’ from main river flooding, while no formal flood defences are in place. Investigations also identified that surface water accumulation to the highway contributed to the flooding, as drainage infrastructure was overwhelmed. A manhole at Cardiff Road, associated to the Ilan Avenue culvert network, also surcharged.
Taff’s Well (Flood Investigation Area RCT 17)
In total, 25 properties (including 11 houses) flooded in Taff’s Well, along with significant highway flooding throughout the area. The report notes that the primary source of flooding in Taff’s Well was the overtopping of the River Taf following persistent and heavy rain. NRW’s gauge recorded the river level to be more than four times higher than its typical level – peaking at 5.49m.
NRW mapping identifies the impacted properties as ‘low risk’ from main river flooding, with defences along the eastern embankment. However, a section of the northern riverbank was identified as having no formal defence. Paired with accounts provided by residents, this information suggests the river initially overtopped at this location – allowing flood water to flow behind the formal defences towards Cardiff Road. The report also outlined that surface water accumulation to the highway also caused flooding and exacerbated fluvial flooding in the area.
Risk Management Authorities and their functions
In the case of all three areas, the relevant RMA in relation to managing main river flooding is Natural Resources Wales, and each separate report details that NRW has carried out investigative analyses in order to understand the mechanism of flooding. It has also commissioned a modelling project to assess the viability of flood risk management options, and developed recommendations to address improvement areas – including the performance of the NRW Flood Warning Service and its incident management response.
The Council is the RMA for surface water flooding at all three locations. Each report details how the Council has carried out significant survey, jetting and cleaning works to infrastructure and has led on development of a Central Control Room to provide a comprehensive response in future flood events. The Council has exercised its powers to engage with NRW and Welsh Water over their responsibilities as RMAs, and worked with NRW to expand the Property Flood Resistance project, offering expandable barriers to high risk properties.
Each report concludes it is unlikely that flooding from a similar event such as Storm Dennis could be prevented entirely, and that RMAs satisfactorily carried out their functions in response to the flooding. However, further measures to improve preparedness have been proposed by all of the RMAs.
Councillor Andrew Morgan, Leader of Rhondda Cynon Taf Council and Cabinet Member with responsibility for Highways and Transportation, said:
“The publication of three further Section 19 reports following Storm Dennis means that the Council has now completed this task for six areas – following Pentre, Cilfynydd and Treherbert last year. These are detailed, fully-accessible reports which are all available to view on the Council’s website.
“The Flood and Water Management Act 2010 requires the Council, as the Lead Local Flood Authority, to investigate the flooding and identify authorities responsible for managing the risk. The three reports published today relate to Treforest, Hawthorn and Glyntaff, and Taff’s Well respectively. For all three areas, NRW is the RMA relating to main river flooding, and the Council is the RMA for surface water flooding. The three reports outline what actions each authority has taken to date, and what functions they also propose to take.
“Since Storm Dennis, the Council has surveyed over 50km of underground watercourse across Rhondda Cynon Taf, created a dedicated 24/7 Drainage Management team, opened an emergency control centre, and installed 26 additional cameras to monitor higher risk locations. More than 400 sets of flood resistant equipment such as expandable barriers have also been issued.
“More than 50 flood alleviation projects have also been completed in local communities, with 50 more being developed. The total investment in flood alleviation within Rhondda Cynon Taf since February 2020 will be more than £13m by the end of this financial year, with a significant number of funding bids by the Council being submitted on top of that total for 2022/23.”