SuDS Report, Land at Hedges, Roydon, Essex
Lead Local Flood Authority: Epping Forest District Council
Further services provided: BRE365 Percolation Test / BRE365 Infiltration Test
Nimbus Engineering Consultants Ltd were commissioned by Construct Land & Homes (Roydon) Ltd to provide a SuDS Report that would deliver a sustainable and effective surface water drainage strategy for a proposed residential development of four detached houses in Roydon, Essex.
The project required a robust SuDS strategy to meet stringent planning and environmental requirements, while overcoming significant site challenges including elevation constraints and limited infiltration options.
Our team devised an innovative solution, integrating a range of SuDS assets to ensure compliance and enhance on-site biodiversity, demonstrating our expertise in the design of Sustainable Urban Drainage Systems.
BRE365 Percolation Test / BRE365 Infiltration Test
To ensure the SuDS hierarchy had been followed and to maximise any infiltration potential at the site, a BRE365 infiltration / percolation test was carried out by our team at the rear of the site.
The BRE365 test showed that infiltration was feasible at the rear of the site, where the ground is approximately 3 metres higher than the front, where a culvert is also located.
Surface Water Management and SuDS Integration
Our surface water management strategy focused on delivering a compliant SuDS system that followed the SuDS hierarchy, ensuring as much of the surface water run-off produced by the development as possible would be dealt with at source.
The key features of our proposed SuDS strategy were as follows:
- Rainwater harvesting tanks
- Green roofs
- Raingardens
- Permeable paving
- Soakaway
- Attenuation tank
Our Technical Approach
The site presented a significant 3-metre elevation difference between the development area and the connection end point. This made installing attenuation systems at the lower part of the site impractical due to spatial constraints. To address this, we implemented multiple flow control chambers, restricting water flow and ensuring efficient drainage across the site.
Biodiversity and Sustainability
Incorporating raingardens and green roofs contributed to Biodiversity Net Gain (BNG) while enhancing water retention and filtration. Permeable paving and rainwater harvesting tanks further supported flood risk mitigation and ensured that surface water run-off could be dealt with at source as much as possible.
This comprehensive approach ensured compliance with source control where feasible, met greenfield run-off rates and reduced flood risk, while also providing amenity, biodiversity and ecological benefits.
Site Challenges and Solutions
1. Elevation constraints: The majority of the development area was located 3 metres higher than the connection endpoint. This elevation difference posed significant challenges for drainage design, as installing large attenuation systems at the lower elevation was infeasible due to spatial and regulatory constraints.
2. Infiltration limitations: While infiltration was technically feasible, several constraints limited the size and placement of soakaways:
- Soakaways must be positioned 5 metres from foundations, reducing viable placement areas.
- Much of the available green space was at a higher elevation, making it unsuitable for drainage systems due to level differences.
- The remaining usable space, located near the development, was too small to accommodate a soakaway large enough to provide full infiltration.
Technical Solutions
- Localised soakaway system: A smaller soakaway was proposed in the limited viable area, effectively managing part of the run-off while meeting regulatory requirements.
- Flow regulation: Multiple flow control chambers ensured controlled discharge, mitigating the challenges posed by the site’s elevation differences.
- SuDS features: By integrating permeable paving, green roofs and raingardens, we maximised water retention and ecological benefits while addressing infiltration limitations.
This innovative and tailored strategy overcame the site’s challenges, delivering an efficient and sustainable drainage solution.
Achieving Planning Approval
The detailed and environmentally conscious surface water drainage design played a critical role in supporting the planning application (currently awaiting S106 consent approval from Epping Forest District Council). By addressing the elevation and spatial constraints and demonstrating compliance with SuDS principles, the project successfully overcame initial objections, highlighting Nimbus Engineering Consultants’ ability to navigate complex regulatory landscapes.
Collaboration and Project Management
Nimbus Engineering Consultants collaborated closely with Construct Land & Homes (Roydon) Ltd to ensure the project’s success. Our proactive communication, on-site problem-solving and commitment to sustainability ensured the design was delivered on time and within budget.
Conclusion and Further Assistance
This project demonstrates Nimbus Engineering Consultants’ expertise in delivering innovative and sustainable surface water drainage solutions under challenging site conditions.
If your project requires specialist engineering consultancy for SuDS design or surface water management, please contact Nimbus Engineering Consultants or email info@nimbusengineering.co.uk.
For more information, visit our dedicated page on SuDS and Surface Water Drainage Design.
