The Newt Ditch Marlow Flood Alleviation Scheme

The Newt Ditch Marlow Flood Alleviation Scheme aims to reduce flood risk to 71 residential and non-residential properties in this flood prone area around the Newt Ditch in eastern Marlow.

We're committed to managing flood risk and this is one of the various projects aimed at managing flood risk across the county.

Update: March 2022

Between January and March 2022, we:

  • assessed the culvert under the A404,
  • carried out surveys of the land east of the A404
  • engaged with Thames Water and National Highways
  • re-costed the project for detailed design and construction costs and submitted for additional funding to the Environment Agency

Further details are set out below.

A404 culvert alignment investigation and survey work

Between January and March 2022, the project team carried out works on the culvert under the A404 to fully understand the condition of the culvert. This work included:

  • excavating the ditch on the east side of the A404
  • removing vegetation on the east side of the A404
  • jetting and removing silt in the culvert under the A404
  • carrying out a CCTV survey of the alignment and condition of the culvert under the A404

It was not possible to complete the jetting, silt removal and CCTV survey inspection works on the culvert due to heavy rainfall. This work will be completed as soon as the water levels in the culvert and ditch recede. 

We also carried out walk over surveys by the lakes and along the watercourse east of the A404 close to Westhorpe Farm Lane.This work has been immensely helpful in deepening our understanding of how surface water should flow along the culvert and east of the A404 towards the River Thames.

We are planning further survey work during the summer.

Engagement with Thames Water and National Highways

We have engaged with Thames Water and National Highways to gain a better understanding of their pipe network contributing to the Newt Ditch flows.

Detailed design and construction costing

We've undertaken a review of the design and construction costs for the scheme. The review reflects the updated scheme design and additions to the scope.

The costs for the scheme have increased and we have therefore submitted a revised funding case to the Environment Agency for additional funding.

We expect to hear if we have been successful by early autumn.

The background

Marlow has a history of flooding. Roads prone to flooding include:

  • Dedmere Road
  • The Croft
  • Quarrydale Drive
  • Fieldhouse Lane

A primary cause of flooding is the lack of capacity in the culverts that drain into the Newt Ditch. A culvert is a structure (a pipe or channel) which allows water to flow under a road, pathway or similar.  

Our scheme is focused around the culvert under Dedmere Road from Fieldhouse Way through to the open channel section either side of the A404.  

We've carried out video camera surveys of the current culverted drainage network which runs under Dedmere Road, Quarrydale Drive and the footpath leading to the A404.

Surveys show this existing culvert is blocked in several places. The cause of the blockages include silt and debris build up, in growing tree roots and utility services pipes.

The flood management project

The key elements of the scheme are:

Dedmere Road

We plan to:

  • remove and divert existing utility services currently within the existing 450mm pipe, and clean and repair the pipe as required
  • construct a new brick manhole at the Dedmere Road and Quarrydale Drive junction, where this will connect to the new open channel section.

Quarrydale Drive

We plan to:

  • replace the existing pipework with a new 1m wide by 1.2m deep open concrete channel over a length of approximately 85m; there will be headwalls at either end
  • provide a new, permeable, riverside footpath including low level lighting

The Acre to west of Gunthorpe Road

We plan to:

  • retain the existing 750mm diameter pipework and cleaned and repair it if required
  • relay the existing footpath and provide new low level lighting

West of Gunthorpe Road to A404 Culvert

We plan to:

  • replace the existing pipework with a new open channel to be formed on the line of the of the existing Newt Ditch, for a length of approximately 225m
  • provide a new permeable access path including lighting

East of A404

We plan to:

  • regrade approximately 100m of the Newt Ditch
  • modify the existing siphon arrangement to improve flow

Benefits of the scheme

There are multiple benefits of the proposed project, including:

  • a reduction in flood damages (£61.4 million) to properties and infrastructure when flooding occurs
  • reduction in the risk of culvert blockage through creating open channels, as blockages in open channels will be easier to identify and simpler to remove
  • additional open channel habitat through extension of the open section of the Newt Ditch
  • health benefits of reduced flood risk
  • reduced costs to the emergency services in responding to flood events
  • reduced costs of evacuation of residents as a result of flood events
  • reduced risk to life from flooding

Next steps

We've revised our project programme to reflect the requirement to seek additional funding and the additional scope.

Between March and June, we'll:

  • update our flood risk model
  • carry out further environmental and topographical surveys

Between July and December, we'll

  • develop the detailed design of the scheme
  • carry out ground investigations
  • update our environmental assessments
  • prepare planning drawings

In January 2023, we'll:

  • engage with the public on our detailed plans ahead of a planning application submission in the spring

In 2024, we'll:

  • carry out construction works

Contact

If you have any questions, or you'd like enquire about how to participate in the scheme, you can contact us:

Telephone: 01189 467809

Email: [email protected]