Submitted to Wealden District Council by Becca Collison on behalf of the Horstedpond Farm Action Group (HFAG)
15 November 2022
The majority of the land covered by the Horstedpond Farm Development Site sheds surface water to the Ridgewood Stream. A major tributary of the River Uck, the stream flows through the northern boundary of the proposed site in an east-west direction and through three of the development’s seven fields. These three fields are designated as a high-risk flood zone 3 area. As can be seen from the photos, these three fields regularly flood during periods of heavy rainfall and the fields themselves often become like rivers. This flooding is a natural process that has been happening for hundreds of years. The fields either side of the stream are ‘natural’ floodplains which absorb excess water that is then slowly ‘fed’ back into the stream and into the River Uck. They therefore help prevent flooding further downstream, for example of the River Uck in the middle of Uckfield town.
If the Horstedpond Farm development is allowed to go ahead, the volumes of surface runoff water will increase significantly due to the provision of extensive areas of hard surface, e.g. rooftops, roads and driveways. Horstedpond Farm’s natural flood management process will inevitably be compromised. The natural floodplains will be need to be augmented by new drainage systems but there are serious doubts about the ability of any of these systems to cope with the volumes of surface runoff in the event of the worst-case storms. There are also concerns about the knock-on effect of these new drainage systems on the flooding of not only the Ridgewood Stream but also the River Uck further downstream.
The Wealden Core Strategy Local Plan (WDC, 2013) SP10 states that developers should “reduce the economic impact of flooding by avoiding allocating land for development in medium and high flood risk areas”. The flood risk report by Stantec commissioned by the developer states that the proposed development will result in a net gain of 6.61 hectares (ha) of impermeable surfaces, which will have negative implications for on-site and downstream flood risk if left unmanaged. The WDC Strategic Flood Risk Assessment Level (JBA,2022) noted that local planning authorities have an obligation to ensure flood risk is not increased elsewhere as a result of development.
Ridgewood Stream is classed as an ‘ordinary watercourse’ and
the developer has been advised that, as the Horstedpond Farm site is some distance away from the River Uck, the Environment Agency (EA) would not expect to see additional fluvial modeling undertaken. However, Ridgewood Stream is a major tributary of the River Uck and the stream transitions from an ‘ordinary watercourse’ to a ‘main river’ classification at the northeastern boundary of the site where it goes under Lewes Road. The flood risk studies undertaken so far have not taken this into account.
Nor has there been any analysis carried out on the flooding risk downstream that would be posed as a result of this development being built.
It is mandated that the drainage system provided must be able to accommodate the maximum rate of rainwater entering the drain in “the worst-case scenario”, i.e. the volume generated by the biggest storm in 100 years plus an additional 40% extra storm rainwater to reflect the possible effect of climate change. The sustainable drainage system (SuDS) chosen for the Horstedpond Farm development is a connection to Southern Water’s storm drain system, augmented by six small attenuation ponds that would be connected to the Ridgewood Stream. In its own submission to Wealden District Council Southern Water stated that “Construction of the development shall not commence until details of the proposed means of foul sewerage and surface water disposal have been submitted to, and approved in writing by, the Local Planning Authority in consultation with Southern Water.” Obviously, some considerable reinforcement of Southern Water’s existing network would be required to accommodate 400 Horstedpond Farm homes.
Attenuation ponds only function properly if they are well designed and maintained, and a number of different disciplines need to be involved to ensure a suitable design outcome that releases runoff water in a controlled way and supports biodiversity. There are no details in the application of the design and maintenance arrangements for these attenuation ponds. Will they be able to accommodate the maximum anticipated runoff volumes? Will a level of water be maintained in the ponds at all times? Who will own and maintain the ponds – the local authority, a housing association or a private company that owns the common land, roads and other infrastructure? Has proper consideration been given to safety issues, particularly the presence of small children in the vicinity of open water?
According to the developer’s plans, the construction of a car park for the site’s Suitable Alternative Natural Green Space (SANG) is proposed for a field next to the Ridgewood Stream. This is one of the flooded fields shown in the photos.
Sewer flooding on the Lewes Road on the western boundary of the site has been citied many times and the Uckfield Surface Water Management Plan (SWMP) map highlights it as a sewer flooding ‘hotspot’. East Sussex County Council (ESCC) recorded eleven incidences of the flooding of Lewes Road due to Ridgewood Stream overflows between 1997 and 2015 and there have been a number of similar incidences since.
Another water-related issue that may come to the fore at Horstedpond Farm is given by the fact that the development of the neighbouring Ridgewood Place housing project, which is situated across Lewes Road on higher ground, has been troubled with groundwater level issues.