Riverside & Water Management
The North Street Quarter water management strategy will not only complete the town’s flood defences, protecting North Street and the Pells, but it will open up the riverside, making it accessible and visible throughout the area for local people and visitors enjoy.
Flood defences for the development must recognise where Lewes is located on the River Ouse. The catchment area of the river covers over 600 km2. In the Lewes area, the catchment extends to Slaugham in the north-west and Sheffield Park and the upper Ashdown Forest slopes towards Crowborough in the north-east.
At times of significant rainfall, huge volumes of water flow into the Ouse and are carried through Lewes. The length of time over which it rains, together with the intensity of the rainfall, will determine when these flows arrive at Lewes and their associated volume. Whether or not Lewes suffers flooding is then a function of how the Ouse catchment handles these rain events, in terms of flow rates, arrival times and upstream storage devices.
The majority of the catchment area lies to the north of Lewes (i.e. upstream) and therefore the improvements made at these northerly reaches of the catchment will significantly affect the flood risk at Lewes. Upstream of Lewes, considerable efforts by the Environment Agency are being made to encourage the management of the undeveloped land, arable acres, woodlands, etc. to be sensitive towards the way in which rainfall run-off happens. This management can, at modest costs, significantly affect the rate of flow and volumes of flood water reaching Lewes at the critical time during a flood risk event.
A university study has produced a flood model that identifies the benefit of installing various natural woodland devices to impede and ‘manage’ the excess flows. All of this will have a positive impact on flood risk for all the towns along the Ouse, with Lewes gaining probably most benefit as it is the second furthest town downstream.
As well as constructing flood defences to protect the North Street Quarter development, we are constructing similar defences in the Pells area. This will complete the town’s flood defences and ensure long-term security for the wider area.
The proposed flood defences are designed for a flood risk level which is set by the Environment Agency and includes a 30% additional allowance for the climate change expected over the coming decades.
Sustainable Urban Drainage Systems (SUDS)
Rainwater run-off will be managed on the site through permeable paving and Sustainable Urban Drainage Systems (SUDS), which use open swales and water gardens instead of drains. As well as managing the run off, SUDS helps attract and support more plant, insect and animal species. Making space for water and designing attractive features to store water within the site also helps alleviate the risk of flooding. Without these measures, water would otherwise gather behind the flood defences. We will create ducted outlets, which will allow the tide to take the water away as it falls, assisting the flow of water into the Ouse.
Enjoying the Riverside
The design of the North Street Quarter scheme will meet the technical requirements of the flood defence strategy with the added benefit of opening up the riverbank, linking the town centre with the Ouse and surrounding countryside. A complementary water strategy, built into the scheme’s design, will provide attractive water features within public open spaces, which will also boost the area’s biodiversity.
The principle public space and riverside features include:
- Two-level riverside walks, including promenade and riverside path, linking the site to Pells, the town centre, Malling Fields and the South Downs
- Multiple viewing points and pedestrian connections and access to the riverside throughout the site
- Public launch access points for small boats
- Swales and open water features will be created throughout the site, creating new landscape and ecology pathways which encourage connections for wildlife through the scheme to the river