The Challenge
Store Property Investments Limited sought planning permission for a new employment park on land in Angmering/Rustington, West Sussex.
The scheme included employment floorspace, ancillary offices, access infrastructure, drainage, landscaping and ecological mitigation. However, the council refused planning permission, with key objections centred on flood risk and drainage matters.
The appeal faced several interconnected challenges, including concerns over compliance with the SuDS hierarchy, the suitability of infiltration drainage, reliance on pumped drainage infrastructure, flood compensation design, discharge rates and water quality management. The Environment Agency and local drainage consultees also questioned whether the proposed flood compensation area would function effectively and whether the development could increase flood risk on or off site.
To secure planning permission, the project team needed a robust technical case demonstrating that the revised scheme was safe, deliverable, policy compliant and capable of managing flood risk without adverse impacts on surrounding land.
The Solution
Arthian provided integrated flood risk, drainage and hydraulic modelling support throughout the appeal process, bringing together multiple technical disciplines to address the objections raised.
Groundwater monitoring and infiltration testing demonstrated that infiltration was not a viable primary drainage solution due to shallow and variable groundwater conditions. This evidence enabled the SuDS hierarchy to be addressed clearly and proportionately.
The drainage strategy was redesigned to remove the original pumped system and replace it with a gravity-fed surface water drainage network. Surface water attenuation was controlled using HydroBrake technology and restricted to greenfield runoff rates, improving resilience, sustainability and long-term maintainability.
Our hydrology and hydraulic modelling specialists tested the revised proposals and demonstrated that the development would not increase flood risk elsewhere. The flood compensation strategy was also fundamentally reworked. Rather than functioning as an isolated basin, the compensation area was redesigned as an open extension of the natural floodplain, allowing floodwaters to enter and leave naturally as water levels within Black Ditch rise and fall.
Survey data and hydraulic evidence were used to address Environment Agency concerns regarding drainage performance and floodplain connectivity. Arthian also supported the development of a planning condition strategy, ensuring that detailed design matters such as water quality treatment, drainage calculations, exceedance routing and maintenance requirements could be secured through appropriately worded conditions.
By integrating flood risk, drainage, groundwater, hydrology and planning evidence into a single technical narrative, Arthian helped present a clear and credible case to the Planning Inspectorate.
The Outcome
The Planning Inspectorate allowed the appeal and granted planning permission for the employment park.
The Inspector accepted Arthian’s groundwater evidence, concluding that infiltration was not an appropriate primary drainage solution for the site. The revised gravity-fed drainage strategy was also recognised as a positive improvement over the earlier pumped approach.
The Inspector found that the submitted drainage and flood risk information was proportionate, robust and policy compliant, with no conflict identified against national or local planning policies relating to flood risk and sustainable drainage.
Importantly, the revised flood compensation design was accepted as a functioning extension of the natural floodplain. Hydraulic modelling demonstrated that floodwaters would rise and fall naturally, with no requirement for external controls and no increase in flood risk elsewhere.
Project outcomes included:
- Successful planning appeal
- Planning permission granted for the employment park
- Flood risk and drainage objections successfully addressed
- Gravity-fed drainage solution replacing pumped infrastructure
- Robust justification of the SuDS hierarchy through groundwater evidence
- Hydraulic modelling demonstrating no adverse off-site flood impacts
- Flood compensation area redesigned as an open floodplain extension
- Final drainage and flood compensation details secured through planning conditions
By combining expertise in flood risk, drainage, groundwater, hydrology and planning appeals, Arthian helped unlock a constrained development site and secure a successful outcome for the client.
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