Solent Combined Sewage Outfall (CSO) spills

August 2021

In June we posted an article on the much improved Southern Water Beachbuoy realtime monitoring of spills into the seas around our coast. The data is limited to which spills might affect bathing water beaches as this comes under more stringent legislation..

During May and June we logged all the spills into the waters of the Solent including the weather conditions at the time. As we have a number of bathing beaches in the area this gives us a reasonable understanding of the frequency with which pollution is discharged. Not everything is covered in which water based leisure activities take place. So for example the top of Southampton Water, the Western Solent and Portsmouth Harbour are not included although there are many CSOs that could affect these waters.

So what were the results?

  • In May there were discharges on 11 days from some 24 different CSOs with a total run time of over 185 hours.
  • In June there were discharges on 12 days from some 45 different CSOs with a total run time in excess of 750 hours.

So in these 2 months alone sewage was being discharged into the Solent somewhere for the equivalent of nearly 40 days. It was quickly apparent that spills were triggered almost exclusively by rainfall and this did not need to be heavy rain or a storm.

June spills were far more intensive than May, which was quite bad in our view. There were many more occasions when spills ran for over 10 hours in a day and the Isle of Wight suffered particularly badly at the end of the month. Some spills ran continuously for two and in some cases three days.

From a layman’s point of view there would simply appear to be inadequate storage capacity in the system to deal with normal rainfall let alone a storm. Indeed in August, when there were storms, the CSOs were unable to cope and there was serious flooding in parts of the Isle of Wight and around Langstone Harbour.  A situation the CSOs were supposed to prevent. So not only are they causing unacceptable pollution they are not even preventing flooding when they are supposed to. Additional housing proposed in the region will only make matters worse.

The CSOs that discharge most frequently are Cowes/Gurnard, Stokes Bay to Southsea, Langstone Harbour, Ryde, Bembridge and Sandown. Within those areas some CSOs are of course more frequent than others but these are the initial areas of concern from the data so far. These outfalls also correspond with data gathered nationally by the Rivers Trust and, we imagine, the Environment Agency.

Just because we have highlighted the above areas does not mean that other areas do not spill on occasions, such as Colwell/Totland, Seaview and Chichester to name three.

Beware going in the water after rainfall and check Beachbuoy!!

Solent Protection Society are writing to the CEO of Southern Water  to ask that Beachbuoy monitoring data is extended to the water leisure activity areas of the Solent not currently covered by Beachbuoy. Not only is this in the interests of water users but it is also crucial to the marine environment and the marine protected areas around the Solent.

We will also be pursuing the short and long term ways to reduce these raw sewage discharges in the future, which may need further legislation.