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Bewl Water mitigation scheme

Bewl Water is part of a complex water resource system built in the early 1970s. It is the largest reservoir in the South East of England holding some 31,000 million litres of water.

Bewl Water serves customers of both Southern Water and South East Water in parts of Kent and East Sussex, some of the driest areas in the UK.

During the winter, water is pumped from the River Medway and the Lesser Teise into Bewl Water where it is stored. Then, during the summer when additional water is needed for public supply, support flows are released from the reservoir back into the rivers downstream of Bewl Water.

These releases ensure that water can continue to be abstracted from the River Medway for public consumption even when flows drop during periods of low rainfall.

However, the support flows released from the reservoir create an un-natural flow regime in the rivers immediately downstream, which is impacting negatively on the environment. The River Bewl feels this most acutely, particularly during the summer, where the average flow can be more than 20 times what would naturally occur.

Water Framework Directive

The Water Framework Directive (WFD) is European legislation that aims to plan and deliver a better water environment through River Basin Management Plans (RBMP), developed by the Environment Agency.

As part of the programme of work to meet the requirements for the WFD, the Environment Agency carried out investigations that identified the need for measures to improve the environment of the River Bewl and to attempt to put in place a more natural flow regime.

Southern Water and the Environment Agency have been working together to identify the measures that will be required to mitigate, and where possible reduce, the impact of Bewl Water on the downstream environment and bring about sustainable and long-term improvements, while protecting the requirements for public water supply. A package of measures is proposed which includes:

  • Passing some of the support flows down the existing
  • Bewl Water to Smallbridge pipeline
  • Targeted river enhancement measures
  • Smoothing of support flows from Bewl Water
  • Management of invasive species

Bewl Water to Smallbridge pipeline

This work will involve passing some of the support flows down the existing pipeline between Bewl Water and Smallbridge so some water is released further downstream into the Lesser Teise and less is released directly into the River Bewl.

This will result in a more natural flow regime in the River Bewl, and won’t change the flow regime downstream of Smallbridge.

Engineering work will be required at Smallbridge to put in place a new release structure into the River Teise as well as some new connections to existing pipework and flow valves and chambers.

The telemetry system will be upgraded and linked to Southern Water’s main control centre. No changes to the existing pipeline should be required.

Targeted enhancement measures

The scheme will address three main issues on the River Bewl, as identified by the investigations carried out by the Environment Agency. These include incisions on the riverbanks caused by fast flows, deteriorating fish habitats and loss of river vegetation.

Targeted enhancement measures including using woody debris to slow flows and create habitat variations, and re-sectioning of the river to create a shelf for marginal vegetation and habitat for invertebrates have been identified for different parts of the river. Southern Water will work closely with landowners and river users to ensure that the measures used are appropriate and provide benefits to all where possible.

As much locally sourced wood as possible will be used to reduce the number of construction vehicles required and minimise the impact of the scheme on the local road network during construction.

Smoothing the support flows

The operational regime will be changed so the release flows from Bewl Water are turned on and off gradually, giving the downstream environment more time to adjust to the change.

With less water being passed down the River Bewl as a result of the works at Smallbridge, the flow within the river will return to a more natural regime.

Invasive species management

The spread of non-native invasive species is a major concern to all river users. Work has been carried out to look at the options required to effectively manage and where possible prevent the spread of invasive species such as Zebra Mussels, Floating Pennywort and New Zealand Pygmyweed within the waterbodies affected by Bewl Water and associated transfers.

Next steps

Our work is underway and will be complete by the end of 2019.

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