Flooding and water pollution
In this section
Hertfordshire County Council are responsible for managing flood risk across Hertfordshire, working with district and borough councils and other local organisations.
Thames Water are responsible for managing wastewater in the Three Rivers District and ensuring that water entering the rivers is of the best possible quality.
Chesham Sewage Treatment Works (STW) treat sewage from the surrounding area and discharges treated effluent into the river according to the standards set by the site permit. The capacity of these works can be exceeded during heavy rainfall, which means possible inundation of the sewage works and the potential to back up and flood people’s homes, roads and open spaces unless it is allowed to spill elsewhere.
In addition to a standard permit, Thames Water have a storm discharge permit from the Environment Agency that allows diluted sewage from Chesham STW to be discharged into the River Chess if the storm tank’s capacity is exceeded.
Recent discharges have occurred when STW have been unable to treat all incoming flows during exceptionally wet weather. While rainfall is the most visible contributing factor, high levels of groundwater also significantly affect flow levels in the sewer network.
In Chesham, Thames Water have found considerable groundwater ingress into the sewage system. Groundwater enters through cracks and leaks in the sewer pipes, surface water runoff from saturated fields, highways, surface water misconnections into the foul sewage system (such as down pipes from roofs). Sometimes, flood water from the River Chess enters sewers directly through manholes. This additional groundwater greatly exceeds the plant's capacity, which was designed strictly for sewage. For this reason, Thames Water must discharge the excess diluted sewage into the Chess to prevent sewage flooding on land.
The Environment Agency work closely with Thames Water to ensure they closely monitor and report back on the storm discharge activity.
Extreme weather events are becoming more frequent, leading to more storm discharge. Thames Water are responding by increasing the treatment capacity of the sewage treatment works, dealing with known sources of groundwater infiltration and conducting further investigations in the sewer network.
Work currently underway includes temporary fixes to increase treatment capacity and reduce discharges, repairs to pipes to prevent groundwater infiltration and a project to increase the capacity at the plant by 39%.
You can sign up to the River Chess Association Facebook page to receive alerts about sewage discharges.
Report an environmental incident
Please call the Environment Agency on 0800 80 70 60 to report:
- damage or danger to the natural environment
- pollution to water or land
- poaching or illegal fishing
- · dead fish or fish gasping for air
- main rivers blocked by a vehicle or fallen tree causing risk of flooding
- flooding from any river, stream, canal, natural spring or the sea
- incidents at Environment Agency-regulated waste sites
- illegal removals from watercourses
- unusual changes in river flow
- a collapsed or badly damaged river or canal bank
Bathing in rivers
The River Chess is not a designated bathing water according to government guidance. Rivers are not sterile environments, and bacteria are widespread both upstream and downstream of the sewage works.
If you choose to swim in rivers or canals, you do so at your own risk.