Case Study: DPT’s Contribution to The Great Wall of Pixham Flood Defence Project
Below Ground Surface Water systems
Overview
In early 2024, DPT was proud to contribute to the Great Wall of Pixham, a flood resilience project in Dorking, Surrey. Designed to protect properties from devastating repeat flooding, this ambitious scheme combined innovative engineering, practical know-how, and local determination to create a robust barrier and drainage system.
Working closely with the property owner DPT helped deliver a tailored sump and pump installation to manage groundwater on the protected side of the new wall — an essential part of making the flood defences sustainable and effective.
Background
Pixham sits adjacent to the River Mole and has suffered numerous floods over the decades. After the severe floods of 2013/14 and the near miss in February 2020, local residents came together to create a solution that would finally protect their homes.
The Great Wall of Pixham was born: a 70-meter-long flood defence barrier built to withstand a 1-in-100-year flood event.
While the wall itself forms a crucial line of defence, managing foul water and groundwater buildup behind the barrier was equally important. Without appropriate drainage, the protected area could have become waterlogged or even contaminated during heavy rainfall.
Objectives
Provide a robust wastewater pumping system to remove foul water from the low-lying “dry” side of the wall.
Ensure pumps could handle debris such as small stones and earth commonly entrained in floodwater.
Minimise wear and tear on the pumps by optimising sizing and reducing duty cycles.
Build in resilience and ease of maintenance, ensuring the system could be serviced or upgraded in future.
Safely integrate the existing well into the drainage system to prevent groundwater accumulation.
The Solution
The design and installation incorporated several innovative measures to meet the project’s challenges:
High-Capacity Sumps
To reduce start/stop cycles and extend pump lifespan, large 800-litre sumps were selected. This sizing also ensured capacity during periods of intense inflow.Wastewater-Optimised Pumps
The pumps can reliably move foul water containing solids up to 50mm, making them ideal for removing any small stones or lumps of earth entrained in floodwater.Specialist Sump Supply
The system was sourced from Direct Pumps and Tanks Ltd., ensuring high build quality and proven performance.Discharge and Non-Return Design
Each pump discharges through a non-return valve to the wet (river) side of the wall, preventing backflow during flood events.
Outcome and Impact
The combination of the flood wall and the sump-pump system has delivered a step-change in resilience for the residents of Pixham:
Key benefits delivered:
Flood Protection: Homes behind the barrier are now protected from major river flooding events.
Reliable Drainage: The wastewater and groundwater system has proven effective through multiple storm events since installation.
Ease of Maintenance: The system design makes it simple to replace pumps or expand capacity without disruption.
Community Empowerment: Residents now have confidence that their homes and livelihoods are significantly safer.
Reflections from The TEAM
“This was a perfect example of how smart engineering and community action can come together to create meaningful change. We’re incredibly proud to have supported the Great Wall of Pixham.”
— Luke Holmes – Technical Specialist“The scale and detail of this system show what’s possible when you look beyond the short-term fixes and think about resilience over decades.”
— Daniel Challans – Head of Sales and Marketing