The water that supplies the River Chess comes mainly from the aquifer and so has the characteristics of water filtered through chalk. The water has a high mineral content, particularly calcium carbonate, which contributes to the unique environment and qualities of chalk streams. However, other sources of water also get into the Chess, including drainage run-off from roads and farmland, which include pollutants like petrol. The outflow from Thames Water's Chesham Sewage Treatment Works also goes into the Chess. Whilst the discharge from the sewage plant has the beneficial effect of helping to maintain flow, these other sources of water can have a detrimental impact on water quality and put pressure upon the river ecosystem.
Pictured left are contaminants on the surface of the Chess resulting from water on roads running off into the channel.
The River Chess Association has been particularly concerned that Thames Water at times discharges a mixture of untreated sewage and storm water runoff into the Chess via the Chesham Sewage Treatment Works (CSTW) outlet. For example, during 2008, they discharged untreated sewage and runoff on 12 separate occasions, in eight separate months, for a total duration of over 40 hours. There were three separate incidents in 2009 totalling 27 hours and two incidents in 2010 totalling 2 h 52 minutes.
Data from 2003 onward demonstrated a marked increase in both the frequency and duration of these releases. These incidents are said to be caused when the capacity of the sewage work's storm surge storage tanks is exceeded following heavy rainfall events. With more housing being built in Chesham, and the possibility of rainfall events becoming more intense as a result of climate change, even more pressure will be placed upon the sewage treatment works.
Current Update: Thames Water continually released sewage into the river between February and June 2014. This has now ceased and Thames Water are committed to carrying out investigations to prevent a recurrence in the future. This was an unconsented release and the Environment Agency are investigating.
Why is this allowed?
Discharges are made under the terms of consent conditions granted by the Environment Agency. One argument put forward for allowing this practice is that these events only happen when there is heavy rain. Therefore, any discharge will take place when the river is flowing at higher levels, which should lead to greater dilution. Whilst this may be true of spate rivers or some lowland watercourses, this does not apply to chalk streams where rainfall has a minimal immediate effect on flow rates. From data obtained by the River Chess Association, it is apparent that on occasions the discharges occur at times of very low flow rates. What is more disturbing is that there have been a number of occasions when no rainfall occurred prior to a discharge event. We also believe that the current continual discharge of sewage, which is caused by groundwater ingress into the sewage works and system, is not licensed under this system and is therefore unconsented. We have raised this with the Environment Agency.
What impact is this having on the Chess?
There is not yet a clear picture of the effects of this practice on the Chess, not least because by their own admission, Thames Water do not:
- Measure the quantity or content of the discharge
- Report the discharges to the Environment Agency
- Warn or inform other river users who rely on the river for their livelihoods or for recreation
- Understand the health and safety issues arising from these discharges
- Carry out environmental impact studies on the effect of this practice
From observations made by regular visitors to the Chess, there is a belief that there has been a significant reduction in fly life in recent years, matching the increase in untreated sewage discharges. Such a reduction will have a knock-on effect on the fish population and their predators. In order to monitor this situation, the River Chess Association conducts monthly riverfly monitoring on stretches of the Chess both up- and down-stream of the sewage plant outfall. To find out more, see our riverfly monitoring page.
Following consistent lobbying by the RCA, Thames Water expanded their storm water overflow storage in Spring 2012, doubling the capacity at the CSTW. This will significantly reduce the chances of future discharges. Thames Water have also set up a system to notify the RCA of any discharges. This has been in place since April 2011 and we were delighted that there were no discharges for many months, despite some very heavy rainfall events.
....And Bad News
The notification system we had established with Thames Water to tell us of sewage releases from the works was stopped by Thames Water at some point in 2013, meaning that sewage releases may have occurred without our knowledge. Following its re-establishment, we were notified of a sewage release into the river on the 14th February 2014. Sewage has been released into the river continuously since that time, meaning nearly 3 months of continuous discharge of pollution into the river. This is the longest, continual discharge of sewage into the Chess that we have ever been aware of.
There are also a number of other problems with the CSTW. Used sanitary towels and nappies are routinely found in the river downstream of CSTW, which is extremely unpleasant for river users, including our volunteers. The works also experienced a number of failures between 2012 and 2014, which led to sewage flooding the site and contaminating neighbouring land, as well as entering the river. Following positive meetings between Thames Water, the Environment Agency, the Chilterns Chalk Streams Project and RCA representatives, Thames Water will be carrying out works at the site to address these issues.
Foam has been frequently observed on stretches of the Chess. The cause of the foam is unknown, but it is apparent that the foam occurs on stretches that include the outflow from the sewage plant. There also appears to be less growth of the aquatic plant Ranunculus (water crowfoot) in the stretches including the sewage plant outfall. The Association are keen to receive photographs or observations relating to foaming events on the river. Please send photos to firstname.lastname@example.org, along with details of the date, time, prevailing weather conditions and location.