Marlow changes underfoot faster than most towns on this stretch of the Thames. Down by the suspension bridge and along St Peter Street you’re on river ground, terrace gravels and alluvium with a water table that moves with the river. Climb towards Bovingdon Green, Munday Dean or Marlow Bottom and you’re onto Chiltern chalk, capped with clay-with-flints on the higher ground. Two different digs, sometimes half a mile apart, and almost every decision that follows, whether plant, shoring or where the water goes, hangs on which of them you happen to be standing on.
The ground under Marlow
The gravels near the river are decent digging, holding a face and draining freely. But on the lower plots you can hit water before you hit formation depth, especially in winter. Planned for, that’s routine: trial holes first, pumps sized before the excavator arrives, trenches poured rather than left open to fill. Discovered on day two, it gets expensive.
Up the hill it’s a different job. Chalk is a sound bearing material and takes soakaways well, but where clay-with-flints sits over it, surface water lingers and soakaways need proper testing before anyone signs off a drainage design. Marlow Common is its own oddity, glacial deposits over the chalk giving acidic, heathy ground unlike the rest of the Chilterns. One more reason to dig a trial pit rather than guess from a postcode.
THE GROUND HERE
- River terrace gravels and alluvium along the Thames. Free-draining, but with a high seasonal water table
- Chalk rising north of the town towards Marlow Bottom and Bovingdon Green
- Clay-with-flints on the higher ground, which changes how soakaways behave
Riverside plots and water
Marlow flooded properly in early 2014. The Thames came over its banks and the Environment Agency had pumps working around Mill Road. The flood warning area still covers the river through Marlow town and Bisham, so if a plot sits anywhere near the water, the flood maps come out before any spade does. Basements and lowered floors this close to the river are buildable, but the waterproofing has to be designed for groundwater pushing in, not just rain running off. Our drainage guide covers how we approach that. In a flood zone a flood risk assessment is normally wanted alongside an application; Buckinghamshire Council and the Environment Agency between them set what a particular plot needs, so ask while the drawings can still change.
Getting plant in and spoil out
The middle of Marlow, taking in High Street, West Street, St Peter Street and Chapel Street, is all conservation area and thick with listed Georgian frontages, and the way in is usually the hardest part of the job. A plot reached through a narrow arch or over a shared drive chooses the excavator for you. There is no arguing with a brick opening. The suspension bridge carries a weight limit, which sends loaded lorries the long way round. That is a detail that costs half a day when it surfaces on the first morning and nothing at all when it was in the programme from the start. Conservation-area rules reach further than people expect, front walls and drives included, so that is another one for Buckinghamshire Council before anything is ordered.
A rebuild off West Street, a new drive at Bovingdon Green, a basement within sight of the water. Whatever it is in SL7, tell us about it. The ground gets looked at before a price gets written.
We work the villages and towns around here on much the same ground.
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