Title : Over the Wall Drainage: Sustainable Drainage for Waterfront Developments
Abstract:
The Geography of the urban coastal strip of West Sussex presents significant issues for surface water management. During winter months, particularly when ground water levels are high, pluvial run-off from the South Downs drains rapidly onto the coastal flood plain and typically enters culverts that drain via tidally constrained gravity outfalls through sea walls.
Potential flood storage inside the defended coastline is very limited and pressure for housing development is increasingly targeting some of the few remaining undeveloped sites further reducing floodplain storage. The expansion of urban areas over recent decades, in combination with the increased intensity of rainfall events associated with climate change, has resulted in storm water flows entering the system at rates that exceed their capacity to drain. Furthermore, as one looks ahead throughout the lifetime of new developments the constraints on the traditional surface water sewer network will increase as a consequence of sea level rise that will further restrict the period during which existing tidal flaps can operate.
Shoreham Harbour in West Sussex is the subject of a major regeneration forming a key element of the Adur Local Plan and the Joint Area Action Plan. This redevelopment offers a unique opportunity to influence the resilience for waterfront developments that, with appropriate design and timely intervention, can minimise the impact of climate change upon surface water drainage in defended coastal environments.
The Lead Local Flood Authority (LLFA) will share how it has been working with developers and consultants to identify more sustainable approaches to the drainage of tide-locked waterfront developments that can also inform best practice not just within West Sussex but beyond.
Audience take away:
- Why a step change is required in the UK to minimize flood risk for defended coastal developments;
- How hydraulic modelling has been used to assess the relative merits of traditional subterranean drainage systems with ‘over the wall’ and shallow drainage approaches in minimizing of flood risk;
- How the outputs of the modelling and review of SuDS approaches has been used to identify proposed changes to the design parameters for defended coastal developments; and
- Some case studies illustrating how alternative approaches to drainage design are being taken forward.
- Details of the remaining lines of inquiry will also be shared and an invitation provided to delegates to contribute data / expertise that can be used to inform the final report due to be published later this year.
