(This article first appeared in the Hill and Valley Magazine - July edition)
Residents and visitors of the iconic Coln Valley and surrounds have for many decades enjoyed the unique Cotswold limestone landscape of scenic river, tributary streams, brooks and beautiful clear springs. Sadly, in recent times it has become apparent that all is not well in the River Coln catchment.
Historically, the Coln has been a pristine clear waterbody of rich riparian habitats and famed healthy brown trout population. For even the most casual observer it has in recent years become a waterbody of increased turbidity demonstrated by current smoky cloudiness of the flow. In many west of England river systems the polluting sources creating turbidity have largely been diffuse surface run-offs from bare soil sites and associated poor farming practices.
Award winning Coln valley farmers
We are fortunate that within the Coln catchment from headwaters of Brockhampton downstream through Withington, Fossebridge, the Colns, Bibury and beyond the land managers are noted for their environmental friendly, sustainable farming practices. The production of food crops and livestock is delivered within ongoing long-term agri-environmental schemes. These carefully selected schemes ensure lowered chemical/nutrient applications often buffering against surface waters with species-rich margin establishment. By skilled management the requisite compliance within Nitrate vulnerable and drinking water safeguard zones of the catchment are also being met.
Pollution sources and mitigation
The consensus agree that the current deteriorating water quality of Coln catchment is largely due to effluent entering surface waters from point sources of Sewage Treatment Works (STWs) and industrial effluent; private septic tanks outfall, road/hard surface run-off, surface waters sewerage system infiltration and domestic waste water misconnection. Climatic change with increased frequency of, and heavier, rainfall has diverse implication. Ingress to sewerage systems and land flooding are negatives.
The increased precipitations also result in improved flows vital for watercourse pollutant dilution as well as topping up essential groundwater levels. These latter results being more positive and demonstrate the complexity of water related systems. Nature based solutions such as reconnecting flood meadows and created reedbed filtration systems are initially costly initiatives but once established can be self-sustaining with low management requirements.
Inadequate and inefficient sewerage systems
Nationwide the UK STWs are under permit from Environment Agency (EA) to allow discharge and emptying of stormwater storage tanks if and when overwhelmed during rain events. There is no permitted storm water spillage during dry weather days. This illegal practice of “dry spills” is happening throughout UK with the actions of several water companies currently being investigated by the EA. These occurrences are worsening polluting levels as they discharge into lower dry weather river flow with less ability for dilution.
Thames Water owns and manages the STWs throughout the Coln catchment. Their final treated sewage discharges are regularly monitored for Water Framework Directive (WFD) compliance. These datasets are indicating links with some unwanted elevated levels for ammonia and suspended solids downstream of effluent discharges. Of a far bigger concern are the stormwater spillages increasing incidence and the lack of regulator monitoring effluent content. This discharge will be made up of raw sewage and partly treated effluent.
Too little too late!
Following public outcry and media coverage for the “state of our rivers” water companies have launched a raft of STW site upgrades with neglected and inadequate infrastructure being addressed. Thames Water are investing in several of their inadequate facilities including a much-needed improvement at Fairford STW.
Inexplicably Andoversford STW has not been included within Thames Water future investment schedule for reducing storm water discharge from its treatment sites.
The issue of increased STWs storm water spillage rates recently led to government legislation by which Water Treatment works were forced to install Event duration monitor (EDM) devices. These devices record effluent discharge durations and can be accessed via various website data. An extremely useful site of is Sewage Map that visually displays near-live EDM output on zoomable map software. The historic spillage data is also displayed by clicking on specific STWs.
Andoversford STW had EDMs fitted in 2020 while Fairford STW began monitoring in 2018. Recent EDM data clearly shows an exponential increase in storm water spillages entering the Coln waterbody from these two sites. There are no readily available records for earlier years!
Fairford STW spilling into lower Coln reaches has recently held the unwanted position of worst polluting site for the whole Thames Water area of 500+ treatment sites. The latest six-month Fairford storm water spillages totalled over 3,300 hours of discharging that averages at over 18hrs/day. Andoversford STW spilled a six-month total in excess of 2,200 hours. Average of 12 hours/day. It is extremely concerning that this pollution of the River Coln catchment has occurred and is increasing every year.
Water quality and monitoring
The Coln catchment is currently rated at “Moderate” quality status having historically been of higher “Good” status rating. The Coln monitoring datasets for the past decade have been scrutinised and interpreted. Indications when comparing annual data for the period 2014 to 2023 are for elevated chemical pollutant levels of phosphate, suspended solids, and toxic ammonia along with lowered dissolved oxygen when sampled from river reaches downstream of Coln valley STWs outfalls. What river water chemical monitoring has taken place in the Coln is at best inadequate and at worst poorly directed. Historically the Coln's regular EA sample sites have been situated in river reaches some distance from any sewage outfalls. There has also been very little and inconsistent biological monitoring in the Coln catchment. Aquatic invertebrates are the optimum means of monitoring surface water biological status. These should be sampled upstream and downstream of suspected point pollution discharge pipes.
Worse still is the disturbing fact that EA do not sample from the partly treated/raw sewage storm water discharges!
Planned sewerage improvements
Fairford STW will soon be getting much needed upgrades with increased water treatment hydraulic capacity and enlarged storm water storage facility. There will also be a surface water infiltration investigation to identify unwanted run offs entering sewerage manholes and pipe defects. This level of investment and associated infrastructure upgrades are desperately needed at Andoversford Thames Water facility.
Future concerns
If all this information wasn’t bad enough then I am afraid that there is another major factor relevant to future Coln quality status. Recent years have seen over-abstraction of the limestone aquifer by Thames Water in order to meet growing domestic, agricultural and industrial needs. The EA are tightening up on abstraction licensing in an attempt to maintain aquifer and surface water levels. Low flows of the Coln's springs, streams and the main river can be very destructive for associated ecosystems and riparian organisms. This ecological and leisure activity need for healthy surface flows has to be balanced with maintenance of groundwater for drinking water supplies.
The Cotswolds Rivers Trust and Upper Thames Catchment Partnership have been getting some success over recent years through initiatives improving the local river water management systems eg. natural flood management methodology. They have recently been joined in their vision of a return to cleaner rivers by the newly established Upper Coln Restoration Group. Funded by a group of local riparian landowners, a consultant, who compiled this article, has been sourced in order to co-ordinate the Coln's restorative strategy and support associated ambition to mitigate any identified reason for not achieving an improved river quality status.
There is an obvious need for public engagement, involvement and contribution for initiatives such as Citizen Science volunteers. Such groups input could increase improved river water sampling and complete river walk surveys. If you are sufficiently interested to get involved and/or have any observations regarding restoring the Coln to previous highest quality then can you urgently make contact via email harveysherwood@outlook.com.
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