The Lidsey Wastewater Treatment Works (WWTW) Catchment Area is an area of the district served by the wastewater treatment works at Lidsey. It covers areas in Barnham, Eastergate, Flansham, Fontwell), Middleton-on-Sea (in part), Norton, Aldingbourne, Slindon, Walberton, Westergate, Woodgate and Yapton.
This is a map of the catchment area: Lidsey Treatment Catchment area [pdf] 2MB
Historically, these communities have experienced foul water flooding of roads and property which has also led to the pollution of watercourses. This has been caused by the foul sewerage system becoming overloaded, as a result of groundwater infiltration, surface water inundation and direct connections of surface water to it. This compromises its functioning, as it is not designed to accept surface water drainage flows or excessive groundwater flows. Such flows should be dealt with by appropriate surface water drainage and land drainage systems.
Flooding has also occurred due to capacity exceedance in the 'main river' network and its tributaries. This has also resulted in fluvial floodwater inundating the foul sewerage system.
West Sussex County Council, in a partnership with Southern Water, Arun District Council, the Environment Agency and local groups, undertook a 'Surface Water Management Plan' (SWMP) for the Lidsey WWTW Catchment Area in order to identify the key reasons for these events and to introduce measures to help reduce their impact or resolve them.
As part of the recommendations, Southern Water Services continue to make improvements to the sewerage network, through the sealing of pipes and manholes to help reduce the impact of groundwater intrusion, and surface water and fluvial water inundation.
To receive a copy of the SWMP including its appendices please contact West Sussex County Council on frm@westsussex.gov.uk.
Development within this area will be required to take account and contribute to the improvement of the existing foul sewerage and drainage network, in line with the actions identified in the SWMP and meet the requirements of the National Standards for SuDS.
Further information about the planning policy for this area can be found in the Local Plan.
Our local validation requirements stipulate that all planning applications in the Lidsey WWTW Catchment Area or identified as within a Local Flood Risk Zone (LFRZ) in the Lidsey SWMP must submit a Lidsey Drainage Impact Assessment.
This is a statement explaining how foul and surface water is to be drained from the application site. This must include what measures will be implemented by the applicant to reduce the impact of foul and surface water drainage in the catchment area.
Applicants are expected to demonstrate that water quality will not be impacted by proposals that may directly or indirectly affect water bodies.
The assessment must refer to the Lidsey SWMP.
If the application site is identified as being in a LFRZ, the statement must identify which zone it is and the predicted flood impact and a summary of flood risk tables must be included. The assessment must then refer to the preferred interventions listed for the specific LFRZ and state which could and will be implemented as part of the proposed development. The LFRZ and relevant pages to refer to into in the Lidsey Surface Water Management Plan are identified on the planning validation interactive map.
The Lidsey Drainage Impact Assessment may be included within the site-specific flood risk assessment for the site. However, designers must signpost this to the applicant and agent as they may need to direct the validating officer to it.
26 November 2025