Lewes New School Development – Flood Risk Assessment Case Study

Lewes New School Development

FPS were chosen by Ben Jones Architects of Lewes to be their preferred flood risk partner for the development of a site at Lewes New School.

This scheme for three houses on land adjacent to the former Lewes New School involves the careful insertion of dwellings onto a backland site, within the Lewes Conservation Area and next to the Listed school buildings. The design is quietly contemporary, not competing with the adjacent buildings but providing a neutral backdrop for them when seen from the street. Development work began in summer 2021, and was completed in 2022.

Teaming up with the adept personnel of FPS significantly increased the prospects of success for this project, a testimony to our unparalleled expertise and long-standing experience in the field. As part of the preliminary proceedings, an extensive site examination was conducted in November 2019.

The application site is occupied by a school situated on a corner plot at the junction between Talbot Terrace and Pelham Terrace. The site lies within a Conservation Area and two of the school buildings are Grade II Listed. The site, currently known as Lewes New School, was historically known as Pells County Primary School and dates back to 1896.

The application sought listed building consent for the construction of three houses on land within the curtilage of the existing school building, which is listed. Alterations were also proposed to be made to the listed building as well as demolition of outbuildings, new landscaping and parking.

The EA’s Flood Map for planning showed that the site is located within Flood Zone 2, land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% – 0.1%), or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% – 0.1%) in any year.

The paramount objective of the Flood Risk Assessment (FRA) was to validate the suitability of the proposed development in light of the prevailing flood risks. FPS meticulously executed the FRA in adherence to the latest local and national stipulations governing development and flood risks by:

  • Assessing whether the site is likely to be affected by flooding from different sources.
  • Providing an assessment of the vulnerability of the proposed development and its suitability in relation to the identified flood risks.
  • Providing an opinion in relation to the likely impacts of the proposed development on flooding elsewhere.
  • Where required, presenting flood risk mitigation measures necessary to ensure that the proposed development and occupants will be safe, whilst ensuring flood risk is not increased elsewhere.

Result: Planning Permission Approved (REF: SDNP/20/00676/LIS) ✅

The FPS Flood Risk Assessment successfully demonstrates that the proposed development:

  • Is suitable in the location proposed and will be adequately flood resistant and resilient.
  • Is unlikely to place additional persons at risk of flooding.
  • Is unlikely to increase flood risk elsewhere through the loss of floodplain storage, impedance of flood flows or increase in surface water run-off (subject to providing the appropriate volume of compensatory storage on site).

The whole site is located within Flood Zone 2, the proposed development is classified as ‘More Vulnerable’, and it has an anticipated lifespan that falls within the ‘2080s’ epoch. Therefore, the central and higher central allowances were considered, which equated to an additional 35% and 45% on flow volumes for Climate Change (CC).

It was proposed that the finished floor levels across the three dwellings be established at a minimum elevation of 6.02mAOD. This specification allows a 300mm freeboard above the flood level for a 1 in 100 year event + 35% for Climate Change (CC) considerations, and a 160mm freeboard above the flood level for a 1 in 100 year event with a 45% CC enhancement. Elevating the finished floor levels to a baseline of 6.02mAOD also helps protect the structures against potential risks from surface water, groundwater, and artificial sources such as sewers.

Externally, it was advised that the ground contours be crafted to slope away from the new dwellings, directing water flow towards the nearest drainage points. The outside spaces are envisaged to embrace the use of permeable paving, alongside compensatory storage for any displaced floodwaters. Through these meticulously designed measures, the development not only increases its own flood resilience but also thoughtfully mitigates the potential impact on the surrounding area.

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