Case Study: The Forty, Cricklade

The site presented several drainage challenges that required careful attention to ensure effective water management. Here’s a closer look at the challenges we faced: 

High groundwater levels: 

The site’s high groundwater table severely limited the use of traditional infiltration methods like soakaways. This made it necessary to explore alternative solutions. 

Surface water runoff: 

Previously, surface water runoff from the property was discharging directly into the private foul sewer network. This practice needed to be addressed and redirected to prevent overloading the system. 

Site constraints: 

Due to limited space, certain SuDS options, such as swales and green roofs, weren’t feasible. The site’s compact nature required a more innovative approach to manage the runoff while fitting within the available space.  

Our Solution: 

To tackle these challenges, we created a tailored drainage strategy that met all local authority planning requirements and adhered to SuDS guidelines. Here’s what was included in our design package: 

1. Site assessment and testing  

First, we conducted a BRE 365 percolation test to assess the site’s infiltration capacity. The test confirmed poor infiltration as a result of the high groundwater levels, which limited the use of traditional drainage methods like soakaways. 

We also reviewed the existing drainage system and private foul network by consulting asset locations plans, providing a clear understanding of the current system’s limitations.  

2. Proposed drainage strategy: 

In order to mitigate runoff issues, we proposed redirecting surface water into a new attenuation storage system. This included the use of crate-type attenuation tanks which were carefully designed for effective stormwater management. 

We ensured that all stormwater discharges were restricted to greenfield runoff rates of 0.4l/s, even for the 1-in-100-year storm event with a 40% climate change allowance. This ensured that the development did not exacerbate existing flood risks. 

We also carried out a hydraulic simulation analysis to confirm that the proposed drainage system would effectively manage stormwater without causing flooding under the new conditions.  

3. SuDS integration: 

Additionally, we reviewed all potential SuDS features in line with the CIRIA SuDS manual and local Lead Local Flood Authority (LLFA) guidelines to maximise the environmental benefits. To manage roof runoff and filter drains, we also integrated rainwater harvesting systems. 

We also incorporated attenuation storage to manage the volume and flow of stormwater, to ensure compliance with both local regulations and sustainable development practices. 

Find a Resilient, Sustainable Solution with Onn Point  

Through a carefully designed sustainable drainage strategy, we were able to deliver a compliant and effective solution for managing both surface water and foul effluent.   

By using a combination of attenuation storage, rainwater harvesting, and filter drains, we successfully improved the site’s runoff conditions to greenfield levels. This approach not only mitigated flood risks but also enhanced the environmental sustainability of the property. 

In summary, our project proudly met all planning requirements and demonstrated how tailored drainage solutions can effectively address site-specific challenges, paving the way for future sustainable development.  

Discover what we can do for your project – get in touch with the drainage design consultants here at Onn Point today!