Case Study: Former Bowling Green, Wolverhampton

Drainage Condition:

The site presented several complex challenges that required an innovative solution, including:

High groundwater levels:

The high groundwater table made traditional infiltration systems, like soakaways, unsuitable. This was confirmed by BRE 365 percolation tests.

Limited space for SuDS features:

Our comprehensive SuDS report found that there was limited space available for larger SuDS features like swales and green roofs, which are often integral to effective surface water management.

Access to local infrastructure:

The site had no immediate access to a nearby watercourse, which made it essential to find a reliable alternative for surface water discharge.

Site levels and existing services:

Aligning proposed site levels with existing services, such as drainage connections and earthworks, required careful planning to ensure compatibility and avoid complications.

Drainage Package

Our approach involved a combination of thorough site assessments, tailored design strategies and effective SuDS integration:

1. Site assessment and testing

We conducted percolation testing in line with BRE365 standards, which confirmed the unsuitability of traditional infiltration systems due to the high groundwater table.

After identifying the location of a public surface water sewer on the northern boundary, we proposed this as the discharge point for surface water runoff.

2. Drainage strategy

To address the surface water runoff, we developed a drainage strategy that directed water to the public surface water sewer, ensuring that discharge rates were restricted to greenfield runoff rates of 2 l/s (subject to Severn Trent Water approval).

We also incorporated attenuation storage through a tanked Permavoid permeable storage system, which allowed us to effectively manage both flow and volume. The design accounted for a 1-in-100-year storm event and included a 40% climate change allowance. This helped to ensure the drainage system could withstand extreme weather events without flooding.

3. Civils package

Our team conducted a thorough review of the site’s external levels, ensuring the proposed finished floor levels, road alignments, and drainage connections were compatible with the existing services.

Additionally, we designed the access roads and parking areas using tanked permeable paving to ensure water management was as efficient as possible throughout the site.

4. SuDS integration

We reviewed all potential SuDS features based on the SuDS Manual, incorporating practical and cost-effective solutions like attenuation storage and permeable paving. Due to space limitations and maintenance constraints, we excluded features like green roofs and swales.

Results

As a result of our talented engineers, we were able to create a fully integrated drainage strategy and civils package that successfully mitigated the site’s challenges and met regulatory requirements. We designed the system to provide approximately 66.73m³ of storage, which was more than capable of managing extreme rainfall events.

Fully aligned with the CIRIA SuDS Manual and local Lead Local Flood Authority (LLFA) guidelines, the drainage strategy, combined with road design and level adjustments, delivered a cohesive, sustainable approach to water management that supported planning approval.

Conclusion

Through a combination of in-depth site analysis, innovative design, and compliance with SuDS guidelines, Onn Point successfully delivered a sustainable and practical drainage strategy for the proposed development at Woden Road. The drainage system not only addressed the site’s challenges but also met the requirements for long-term flood resilience and environmental sustainability.

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