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River Misbourne

We're improving our sewer network in the River Misbourne valley. This covers Amersham, Chalfont St Giles, Chalfont St Peter and Denham. 

The River Misbourne often floods during wet weather. After the wettest winter on record, the river is currently flooded at many locations. We expect high groundwater levels to continue for several months.

What we're doing

  • Managing flows in Chalfont St Peter and Denham, using tankers and/or mobile pumps
  • Managing traffic in Chalfont St Peter high street, for the safety of the public and our staff
  • Balancing the outflow from the Amersham storm tanks, to protect customers from flooding, and minimise discharges to the river
  • Filtering as much of the diluted discharge as possible, to minimise the impact on the river
  • Continually monitoring the river and liaising with the Environment Agency


Since 2021, we've been investigating the points where river and groundwater enters the sewer network. By sealing these points, we're stopping the water entering the sewers in the first place.

We've completed the first phase of chamber sealing. The second phase of investigations are ongoing.


The extra water from river and groundwater flooding has filled our sewers. Some of the sewers in this area aren't designed to hold flood water. This has caused sewer flooding in the centre of Chalfont St Peter and further downstream in Denham.

Because rainwater soaks into the ground slowly, groundwater levels can continue to rise long after the rain has stopped. This means it will take a long time for the extra water to leave our system, even once the rain stops.

The Amersham storm overflow tanks are full and discharging into the river. These tanks were installed in the 1970s to prevent sewer flooding. Find out more about storm discharge and how we monitor it.


We're responsible for maintaining our sewer network and have a long-term sewer flooding prevention plan. We're working towards reducing storm overflow usage to improve river health. Our storm discharge map shows where discharges are happening in near real-time.

Local authorities and the Environment Agency (EA) are responsible for groundwater, river and surface water flooding. We'll be working with them to manage flood water entering the sewer system.