Sherborne's Sewage

Roger Davies

— 3 min read

I continue to look into the very concerning issue of the sewage that leaves Sherborne, goes to Bourton, and gets dumped in the River Windrush. As you know, the Sherborne Brook Support Group is a member of the Windrush Catchment Partnership (WCP). Indeed, we sit on the steering committee.

In advance of the Windrush Catchment Partnership Spring Meeting that's occurring in a couple of weeks' time, I have asked the Chair to submit some questions from us in Sherborne, in advance, to Thames Water who always send a rep.

What follows is a bit detailed, and based on a lot of research, but I think it's important. The absolute abbreviation of these issues is that:

A. Our sewage, more often than not this year so far, has been dumped into the Windrush

B. Thames Water developed a plan to deal with this in 2021. It seems to me to be deliberately opaque. Bourton STW is a priority yet doesn't seem to be getting the attention (£££) it needs

C. Remediation done 3 years ago appears to have had no effect.

D. Data and reporting of data is poor

E. Thames Water claim they will meet all targets for storm discharges here by 2050. They cannot show us their plan to do this. 2050 is a long way off.

I have asked the following specific questions:

  1. The Bourton Sewage Treatment Works (STW) upgrade to triple its flow rate capacity was scheduled to be completed in 2023.  Without any explanation, completion of this has slipped every year to now "Spring 2026" QUESTION FOR TW. Is this Upgrade completed or imminent, and has the capacity increased as this was being worked on? Why has the program upgrade to a priority STW slipped so often without explanation?
  2. The broader commitments to improve the situation were assigned to a Price Review process in 2024 ("PR 2024").  This appears to be on hold so we have no handle on what future work is planned. No remedial works to the sewers have occurred since 2022/2023 according to TW documentation, but we know some happened in late 2025.  None appears to be planned. Continued discharges suggests that the lining and manhole work has had limited effect and discharges in 2024 and 2026 so far appear worse than ever. Ofwat's PR24 final determination placed Thames Water's enhancement expenditure behind a contingent delivery mechanism, pending greater clarity on the company's financial position. Whether post-2026 remediation works are funded remains unknown to this Partnership. QUESTION FOR TW. What are the plans for remediation at the moment? 
  3. Given that a single discharge from 20th January to 2 March this year ran for 1014 hours, so far this year Bourton STW is discharging more often than not. That’s an appalling situation given the remediation already undertaken, and an apparent lack of any plans going forward.  In October 2024 TW assured the WCP that the remediation in 21/22 appeared to have reduced discharges by 50%.  Yet the 2024 figures show it was the worst year for discharges ever. QUESTION FOR TW. How do they reconcile these two statements?
  4. We are currently blind to 2025 discharge data. TW must have this data already. Given the importance of discharges to the WCP and the fact that 2025 data , given extreme low rainfall, will allow very useful analysis it would be good to have this early rather than wait till the end of 2026. QUESTION FOR TW. Is it possible for you to provide the 2025 data now? 
  5. The 2021 plan appears to be failing. QUESTION FOR TW. Is the 2021 management plan going to be updated, in the light of poor (worsening) performance in 2024 and 2026 and if not, why not? 

I'll let you know how it goes. If that's all too depressing, here's some cheer. This is the first snakeshead fritillary of this Spring, on the banks of the beautifully clear and sewage-free, silt-free Sherborne Brook

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