Roundmoor Ditch forms much of the northern and eastern boundary of Dorney Parish.
Roundmoor Ditch, despite the name, is in fact a chalk-fed stream that rises in Taplow and flows southeast, under the Jubilee River, to Dorney Common. There, it is joined by the Cress Brook and continues as the Boveney Ditch, until it joins with the River Thames.
Over the years, Roundmoor Ditch has not been of concern to Dorney residents. However, in the winter of 2014 the Thames Basin suffered significant flooding. This included extremely high groundwater levels in many areas, including Slough. Surface water infiltrated the sewer systems and overwhelmed the sewage treatment works.
Under these extreme conditions, the Thames Water sewage treatment works in Slough were permitted to discharge storm flows into the Roundmoor Ditch. This continued for an unprecedented period of about three months.
Significant concerns were raised by residents in Eton Wick, community groups and landowners which highlighted that the public highly values the river, its ecology and its use as an open space for people to enjoy.
Thames21, in partnership with Thames Water, embarked on a two-year project in 2017 to restore the series of waterways at Roundmoor to a significantly better state than before the 2014 pollution incident and to address community concerns.
Dorney Parish Council Meeting 21 September 2021. Item 30.3 Roundmoor Ditch
Report from Cllr. Stopford:
Cllr. Stopford confirmed that Thames Water stated they will be clearing the section of the Roundmoor Ditch, which runs past their treatment plant in the next week following confirmation that there are no water voles on site.
He also attended a meeting to discuss future plans for the water treatment plant outflow, where it was confirmed that there will be a new pipe through Dorney Common to the Thames at Boveney to help cope with the envisaged population growth and storm water. This will be starting in 2023 and completed by March 2025.
Dorney Parish Council Meeting 20 July 2021. Item 4.3 Roundmoor Ditch
Report from Cllr. Stopford:
Flooding on Dorney Common and plans for Slough Treatment plant outflow.
Firstly, the Hydrology Survey of the Roundmoor and Boveney Ditch Streams
The preliminary findings indicate:
- The gradient through the Roundmoor Stream and Boveney Ditch Stream – from the downstream end of the syphon to the gravel riffle upstream of the Thames River outfall bridge is approximately 1:1750.
- The survey identified two gravel riffles on the lower Boveney Ditch Stream which impound the gradient approximately 800m upstream – biological indicators of this impoundment are present in the form of ‘slow flow loving’ aquatic plants such as Potamogeton or Pond Weed, upstream of the gravel riffle locations (see drone image attached).
- The drone photograph attached highlights the biological indicators of the impounded lower Boveney Ditch Stream. The presence of the downstream gravel riffles, located in the top right of the image, show reduced in-channel vegetation – indicative of faster flows over a shallow bed. The impounded reach of the lower Boveney Ditch Stream, in the bottom left of the image, shows heavy vegetation coverage which indicates slow flow velocities.
The plan is to come back to complete the survey between 14/07/2021 – 20/07/2021, after which a final report will be available.
Secondly the public stakeholder engagement regarding what to do with the outflow from the works will be happening in the Autumn. I have asked that Dorney Parish Clerk can be added to the contact list for this process.
Clearance of the Roundmoor at the Treatment works.
Rosemary Waugh from Thames Water has now had a quote in from their contractor (Maydencroft based in Dorney) and it is now with their Ops team to consider. One thing she has been advised on by their biodiversity team is there is a lot of tree clearance to be done which ideally would take place after bird nesting season has finished (i.e. October)
30 June 2021: Presentation by Thames Water re Slough Sewage Treatment Works options to mitigate problems: Presented to Cllr. Stopford.
15 June 2021: Dorney Parish Council Meeting: Cllr. Stopford reported that he had met with Thames Water on site who had agreed to escalate the issue of clearing out their section of the ditch but he wasn’t overly optimistic anything would happen. He also noted that the Slough Waste and Water Treatment Plant were encountering problems with complying with government regulations concerning ammonia levels and the releasing of water. They would be putting forward three options for consultation in the Autumn – that water (95% of which is treated discharge from the sewage works; however if there is too much rain the discharge would be untreated) be discharged into either the Jubilee River, the Thames or the ditch at Eton. Problems would only get worse with the increasing catchment population. He further noted that the groundwater collecting on the Common had arisen from an incorrect level of added gravel and a Hydrology Survey was being undertaken.
14 April 2021: Dorney Parish Council has been sent a copy of a letter from DEFRA to Joy Morrissey, our M.P., dated 14th April 2021, regarding the floods and flooding risk from treated and, on occasions, untreated sewage flowing into Roundmoor Ditch and then into the Thames (not the Jubilee River) from the Thames Water Slough Sewage Treatment works.
14th April Letter DEFRA to Joy Morrissey
- The letter includes the following:
- In February 2021, an incident was reported to the EA’s Incident Hotline in relation to possible sewage pollution in the Roundmoor and Boveney Ditches. An environment officer attended the site and confirmed that Slough Sewage Treatment Works had made a discharge of settled storm sewage to the Roundmoor Ditch. Thames Water has stated that Slough Sewage Treatment Works was fully treating the required amount of sewage, and that this overflow of storm sewage was made as a result of rainfall. The EA has requested some flow monitoring data from Thames Water and is in the process of analysing this data to assess whether this storm overflow discharge was made in compliance with permit conditions.
- Thames Water is also currently investigating a longer-term solution to reduce the impact of Slough Sewage Treatment Works discharges on the Eton Wick watercourses, including the option of moving the effluent outfall to a different watercourse. The EA has been in discussion with Thames Water on this matter and will assess any proposal to determine if it is environmentally acceptable. Thames Water is currently assessing various options and it is expected that they would engage with local interest groups before a change of this nature is made.
- The water situation in this area is complex. In dry weather, the majority of the flow within the Roundmoor and Boveney Ditches are made up of treated effluent from Slough STW. The hydrology of the area in times of flood, and how groundwater, rainfall and the effluent from Slough STW interact to cause flooding of local watercourses and Dorney Common, is complex and not fully understood. There are some areas of breached bank and cattle poaching that may be further contributing to the flooding of Dorney Common.
- Statutory Drainage and Wastewater Management Plans are expected to be completed by all companies in spring 2023. Those companies, including Thames Water, will be consulting on their draft plan in summer 2022, on which your constituents will have the opportunity to comment.
- Dorney Parish Council, through Cllr. Robert Stopford, will monitor this carefully in future and will support the Eton Wick Waterways Group, as required.