The Old Post Office Berrick Salome
The Brief
RIDA was appointed to undertake a detailed flood risk assessment for a proposed residential development at The Old Post Office, Berrick Salome (OX10 6JN).
The project involves the demolition of an existing workshop and studio building to facilitate the construction of a new three-bedroom dwelling, known as “The Studio House”. Classified as a ‘More vulnerable’ development with an estimated lifespan of 50 to 100 years, the site required an assessment to ensure long-term flood resilience and sustainability.
Why the Client Chose RIDA
Developing a site with varying local flood risks requires specialised hydrological expertise to ensure a smooth planning process.
The client required a consultancy capable of delivering a detailed flood risk assessment that strictly adhered to the National Planning Policy Framework (NPPF) and local South Oxfordshire District Council standards, providing reliable, sustainable mitigation strategies for multi-source flood threats.
The Challenge
While the site is advantageously located in Environment Agency Flood Zone 1, indicating a very low risk of fluvial or sea flooding, it presented other significant technical constraints.
The primary challenges identified were a high risk of surface water flooding, with a strong likelihood of localised deep ponding, and a high risk of groundwater flooding. British Geological Survey data indicated the potential for groundwater emergence above the existing ground level, establishing a challenging design flood level of 55.3m AOD for the site.
The RIDA Difference
To comprehensively address the site’s unique constraints, RIDA conducted a detailed flood risk assessment that targeted the high surface water and groundwater threats.
Because the design flood level was dictated by the groundwater flood level (55.3m AOD), RIDA developed a precise mitigation strategy. This included setting ground floor threshold levels higher than 0.25m above ground level to provide a safe freeboard, alongside specifying the installation of a tanking membrane up to 0.3m above ground level to prevent groundwater ingress.
Furthermore, RIDA incorporated safe flow paths around the proposed dwelling to manage any potential groundwater emergence.
To mitigate surface water risks and prevent any increase in off-site flooding, a Sustainable Drainage Systems (SuDS) approach was implemented. This included the use of permeable paving in the external areas to replicate the existing natural infiltration regime.
Finally, a clear evacuation route was mapped out via Berrick Prior, ensuring occupants have safe egress away from the extent of extreme flooding.
The Outcome
The detailed flood risk assessment successfully demonstrated that, subject to the proposed mitigation measures, the new three-bedroom dwelling can be developed safely and sustainably.
By establishing clear floor levels, resilient tanking measures, and a SuDS-compliant surface water strategy, RIDA provided the robust evidence necessary to support the planning application and prove compliance with NPPF provisions without increasing flood risk elsewhere.