Case Study: 84 Ditton Rd, Surbiton

The Challenges

The site presented several challenges that required innovative solutions:

No formal drainage system:

The site was undeveloped garden land, which lacked any formal drainage infrastructure.

Unsuitable infiltration conditions:

Local borehole data revealed that infiltration to the ground was not viable due to the presence of London Clay Formation. This meant traditional soakaways unsuitable.

Space constraints:

The limited space available for drainage solutions was further restricted by tree root protection areas, which prevented the use of certain overland SuDS features like swales.

Flood risk management:

Our team needed to ensure the site was designed to manage surface water effectively, especially during extreme rainfall, to prevent flooding.

Our Drainage Package

We proudly developed a tailored sustainable drainage strategy that addressed the site’s challenges and complied with regulatory requirements. Here’s how we did it:

1. Site assessments:

Conducted comprehensive desktop studies to analyse site constraints and local ground conditions.

2. Borehole data utilisation:

Used local borehole data and ground investigation reports to confirm the presence of stiff clay, supporting the decision to exclude infiltration methods.

3. Drainage strategy:

Directed surface water runoff to the existing public surface water sewer on Ditton Road, ensuring discharge rates were restricted to greenfield runoff rates of 2.0 l/s.

4. Attenuation solution:

Integrated a tanked Permavoid permeable storage system beneath the parking area for effective stormwater attenuation, ensuring the system could handle a 1-in-100-year storm event, plus a 40% allowance for climate change.

5. Water reuse:

Incorporated a water butt to manage runoff from green landscaped areas to promote water reuse and sustainability.

6. Foul drainage:

Proposed the direct discharge of foul water to the public foul sewer located on Ditton Road, ensuring compliance with local sewerage requirements.

Results

The drainage strategy effectively met all regulatory standards and the client’s objectives. Surface water runoff is now properly managed, effectively reducing flood risk and ensuring compliance with greenfield runoff rates. The design fully complied with CIRIA SuDS Manual guidelines and local authority standards, which helped to streamline the planning approval process.

Sustainability was a key focus, with the integration of water reuse solutions such as a water butt for landscaped areas, promoting environmental responsibility. The tanked Permavoid system provided the necessary attenuation capacity, managing approximately 66.73m³ of runoff from extreme rainfall events, making sure the system could handle the site’s stormwater needs effectively.

Conclusion

The drainage strategy created by our drainage design consultants successfully overcame the site’s unique challenges, including poor infiltration conditions and space constraints. By leveraging effective SuDS solutions like permeable storage systems and water reuse provisions, we delivered a sustainable, compliant, and resilient drainage package.

The project’s success highlights Onn Point’s expertise in providing tailored solutions that meet both environmental and regulatory standards to delivery long-term sustainability and flood resilience for developments.

Want to find out how we can transform your project? Get in touch or get a quote with Onn Point today!

Explore our other case studies here.