- 17th November 2022
- Posted by: Dom Senior
- Category: Projects
Client: Vale of Glamorgan Council Location: Dinas Powys, Wales
In December 2020, the Vale of Glamorgan experienced an extreme rainfall incident which led to an estimated average of 33mm of rain over an 11-hour period. The storm is reported to have been equivalent to a 1 in 20-year rainfall event, which generated a fluvial return period of between 10 to 20 years. As a result, the surface water sewer network was unable to cope with the large volume of water, further exacerbating the flooding. This led to both the River Cadoxton and East Brook overtopping their banks at multiple locations, causing flooding to more than 100 properties.
Over the course of this project, our team were required to provide a variety of services, which were split into three stages.
Stage 1 – Flood Reconnaissance
In January 2021, we were commissioned by Natural Resources Wales (NRW) to collect, review, and analyse data from the storm event of 23 December 2020 for the purpose of producing maximum flood extent outlines for Dinas Powys.
On the 6 and 12 January 2021, our team and a team from Storm Geomatics visited the area affected by flooding to conduct a post-flood event survey.
The objectives of these visits were to:
– Identify maximum flood levels and extents
– Note areas/properties flooded
– Determine the impact of infrastructure
– Where possible, identify flood mechanisms
– Note and photograph damage to assets, for example, bank slips and erosion
Survey teams used geotagged photographs and written notes to collect the post-flood survey data alongside photographs and videos from residents, taken during and after the flooding. This data was then combined to derive the maximum flood outlines for Dinas Powys.
Stage 2 – Section 19 Report
The flood reconnaissance study we conducted documented widespread flooding throughout Dinas Powys. As a Lead Local Flood Authority (LLFA), The Vale of Glamorgan Council (VoGC) therefore had a duty to prepare and publish the results of investigations into significant flood incidents, as detailed within Section 19 (S19) of the Flood and Water Management Act 2010 (FWMA).
In May 2021, we were commissioned to complete a Section 19 Investigation to provide a factual report of the December 2020 storm event and subsequent flooding across Dinas Powys. This followed an initial commission by VoGC to compile an account and analysis of the meteorological and hydrological data of the event, in order to support understanding and provide an estimate of the event frequency.
Stage 3 Challenge – Dinas Powys PFR Scheme
Following the completion of the S19 report, we were then appointed by VoGC to undertake a Property Flood Resilience (PFR) scheme in Dinas Powys for properties affected by the flooding. One of the key challenges of PFR schemes such as this is engagement with the community and encouraging property owners to sign up for the scheme.
Across Dinas Powys 302 residential and 5 community properties had been identified as eligible for a PFR survey based on impacts during the December 2020 flood event and modelled flood extents. Residents were sent a letter from VoGC with instructions on how to register for the scheme using our bespoke online ‘JPROP’ portal. These instructions also included a contact number for the Resilience team, which could be used by property owners that were less familiar with the technology. In order to achieve a high proportion of engagement, we also issued a series of reminder letters to residents who didn’t respond to the initial communication.
In total PFR surveys were carried out at 180 properties to determine the impact of flooding and the suitability of installing PFR measures. Following the surveys, each property owner received a bespoke PFR report including a detailed property description, local and individual flood history, an explanation of various sources of flood risk and recommendations for suitable PFR measures. The report also included advice on how residents could adapt the internal areas of their property to become more resilient to flood damage, including suggestions for raising electric sockets and replacing carpets with flood-resilient flooring.
The aim of the PFR scheme was to reduce the impact of both fluvial and surface water flooding during any potential future flood events, through the provision and installation of PFR measures. These included flood doors or door barriers, automatically closing airbricks, pumps and non-return valves.
Throughout the survey process, the JBA team engaged with residents and highlighted the importance of emergency plans and the effective storage and maintenance of PFR products, to prolong their effectiveness and longevity. As a result of the PFR scheme, 180 properties across Dinas Powys will benefit from added protection and preparedness for any future flood events.
A bespoke report was written for each property, identifying options and recommendations for PFR measures which might help improve property flood resilience. The survey findings were also used to inform the council’s Business Case in their application for Welsh Government Funding to supply and install PFR measures.
“Following extensive flooding in the east of the Vale JBA were engaged by the council to provide specialist advice and assist with a number of Section 19 investigations. In Dinas Powys this led to further work developing a business case for the installation of PFR measures across the community. As part of this process JBA have undertaken a large number of property inspections to a tight programme, whilst also dealing with the associated challenges and last-minute cancellations along the way. The project team were easy to work with throughout providing clear advice, guidance and accommodating changes in scope as the need arose.” Clive Moon, Engineering Manager, Vale of Glamorgan Council.
Want to know more?
For more information about this project, please contact Beth Jones.