Large garden drainage – Cobham
An engineered drainage solution on London Clay in Cobham — 400 metres of perforated land drains, ACO channels, soakaways and a new Indian sandstone patio around the existing pool, designed and built in-house by Flourish Landscaping.
The problem: a waterlogged garden
Water was the real problem in this large Cobham garden. Sitting on heavy London Clay, broad stretches of lawn stayed saturated for days after rain, turning much of the garden into no-go ground for weeks at a time and undermining everything planted in it.
Client brief
The owners wanted a long-term fix rather than another seasonal patch-up. Their children used the garden daily, so it had to drain reliably and stay genuinely usable — not just look dry for a fortnight after the works finished.
Project scope
- Diagnosis and resolution of recurrent garden flooding on London Clay
- Design and installation of a comprehensive underground drainage network
- Around 400 metres of perforated land drains in geotextile-wrapped gravel channels
- ACO channels to intercept surface water
- Soakaways to disperse collected water
Description of works
Design approach
Led by Craig Davis BSc (Hons) Horticulture, the turning point was recognising that the problem lay not in the lawn but in the soil profile beneath it. London Clay holds water and drains painfully slowly, so the answer was an engineered system that gives surplus water somewhere to go — the diagnostic thinking we bring to every flooded garden and drainage project.
- A submersible dirty-water pump with tube float for added flood protection
- A new Indian sandstone patio around the existing pool
- Around 80 cubic metres of imported topsoil to restore growing conditions
- New lawn establishment and landscape restoration
Pump system and soakaway installation
For added flood protection, a submersible dirty-water pump with a tube float was installed at a strategic low point, working alongside soakaways to move and disperse water away from the worst-affected ground — a belt-and-braces approach for a site that clay alone could never shed fast enough.
Construction details
Some 400 metres of perforated land drains were laid in clean gravel channels wrapped in geotextile membrane to stop fine clay silting up the system — the detail that decides whether a drainage scheme lasts years or fails in months. ACO channels were set to intercept surface water, all feeding the soakaway and pump network. As APL- and TrustMark-accredited landscapers, this is engineering as much as landscaping, and it was built to last.
Patio installation around the pool
Once the drainage infrastructure was complete and ground levels had stabilised, attention turned to the new outdoor living space: a generous Indian sandstone patio laid around the existing pool on a properly prepared, free-draining base, tying the garden back together as a place to enjoy rather than battle.
Soil improvement and landscape restoration
To rebuild healthy growing conditions and support new lawn establishment, we imported roughly 80 cubic metres of quality topsoil, restoring a workable profile above the new drainage so grass and planting could finally root and thrive — the soil-first thinking we set out in our advice on improving clay soil.
Results
The garden now clears water within hours instead of days. Grass density has improved markedly across two seasons, the children have their garden back year-round, and a plot that was effectively unusable in winter is reliable in all but the worst weather. It is the kind of result that sits behind our 5.0 rating across 51 Google reviews.
