Since our inception, FORQ have wanted to quantify as best we can the state of our two rivers. We also want to enhance that knowledge with our own contribution through , citizen science based wildlife recording, riverfly and now water quality monitoring. We want to do this to establish a fact-based picture of the ecological and environmental health of our chalk stream catchment that provides a benchmark that future improvements (or deterioration) can be measured against.
This article brings together information gathered from the Environment Agency through their Data Catchment Explorer, industry data collated by The Rivers Trust and information taken from the Defra sponsored Chalk Stream Restoration Strategy 2021 chaired by Charles Rangeley-Wilson. Much of it was first presented as part of our Spring 2022 Public Meeting in High Cross.
A healthy chalk stream is an incredibly complex and diverse environment, fundamentally dependent on three elements to be ecologically healthy. Natural flow, natural habitat and clean water together all contribute to create a chalk stream that is ‘greater than the some of its parts’.
To assess the state of our two rivers and their ecological health, let’s look at each of the elements in turn.
“Restoring high-quality physical habitat to the chalk stream is fundamental to realising the full potential of any other improvements made in flow and water quality. Habitat quality is where all elements of a good restoration strategy come together.
“And yet, while it is relatively easy to appreciate that an unnaturally depleted, dry or heavily polluted river is in a poor state, it is much more challenging to read a river and interpret what is wrong with it physically.”
“Good-quality river restoration requires a resolved understanding of what one is trying to restore, informed by a knowledge of the history of the river and the processes which have shaped and continue to shape it.”
Three quotes from the River Restoration section of the Chalk Stream Restoration Strategy that illustrate why expert advice is needed at a catchment level and why we have been pleased to be able to work with Herts & Middlesex Wildlife Trust and introduce landowners and parish councils as they consider improvements for individual stretches. Sarah Perry, Living Rivers Officer at HMWT highlighted the growing list of projects that are either close to implementation or in the planning in the Rib and Quin Catchment at her recent presentation at our public meeting.
There is however much still to do in the catchment to improve the habitats of our rivers. There are physical barriers in the form of weirs and fords at a number of points (the Bengeo project in the graphic above is addressing one, with the removal of a weir), historic dredging in many stretches has isolated the river from its floodplain and invasive non-native species continue to present problems on our river banks. Himalayan Balsam and Giant Hogweed are two plants particularly prevalent in our catchment, as is the Signal Crayfish which displaced our native species at the end of the last century in our chalk streams. Mink too present a problem to the return of healthy numbers of the iconic water vole.
The quality of the water in a chalk stream has a significant impact on the species, be they plant, invertebrates, fish or mammals that live in them. By its very nature the water in chalk streams is of the highest purity and consistent temperature, having percolated through chalk strata for some months before emerging from springs to feed the river.
However, not all the water that enters the river derives from springs and much of it brings pollution with it, in the form of agricultural and urban run-off, soil turbidity and treated and untreated sewage.
In the UK, the body tasked with monitoring the environment including our rivers is the Environment Agency. They take and collate a number of measurements which are then published in digestible form on their Catchment Data Explorer portal. The graphic below shows the location reference given on the website, which might be the point at which measurements are taken. For interest I have also located the Sewage Treatment Works that release to our rivers, which would suggest that the sampling points don’t perhaps measure the ‘worst’ of the rivers, if the EA location references are indeed the sampling points. The current overall classification for each river sub-catchment for 2019 is also shown below.
The overall classification is derived from an assessment of a number of sub-classifications, which have been measured consistently for a number of years. The historic and current data available covers the years 2013-16, with a gap to 2019 and is presented in the tables below, indicating that our rivers have been in a poor to moderate ecological, biological and physio-chemical state for a number of years and have a mixed historic record and current problem with chemical and priority substances.
The chemical pollutants impacting our rivers derive from a number of sources;
‘forever chemicals‘ like PBDE and PFOS are predominantly passively transported to our rivers from the general environment, whilst phosphates, nitrates, and pathogens come from agriculture and sewage, with treatment work discharges also adding to the mix. The graphic below gives more detail.
The company responsible for sewage and groundwater in our catchment is Thames Water and in that capacity they have a significant direct impact on the health of our rivers through the effectiveness of their operations and infrastructure. The historic development of that infrastructure has produced the current sewerage network with lower grade village or town sewage treatment works predominating anddischarging treated sewage commensurate with their age and capacity. This unfortunately means that we are also prone to spills of raw sewage when the system reaches capacity due to extended weather events, though this is supposedly only in ‘exceptional circumstances’. To understand the extent of these sewage spills, we must look to The Rivers Trust.
The Rivers Trust have for several years now been analysing water company and sewage licensing data on an annual basis to build maps of untreated sewage spills across the country.
The Table below collates raw sewage discharges for 2019 and 2020 and indicates some rather alarming and wide-ranging statistics;
In 2019 Barkway STW discharged raw sewage for 175 hours, which increased even further to 548 in 2020. Therfield STW had no raw sewage discharges in 2019, yet 274 in 2020, despite a flat population of 550 since 2015 or before.
The latest figures for 2021 have just been published and unfortunately it is not an improving picture. Therfield again suffered with 243 hours of raw sewage discharge (over 10 days!) whilst Barkway again unfortunately topped the charts with an astronomical 734 hours, or to put it another way, a whole month of raw sewage being dumped into the River Quin.
To return our two rivers to any semblance of their former glory and volume we must now turn our thoughts to the supply of our water.
Due to the remarkable quality of water that derives from a chalk stream landscape, Affinity Water who are the company that supplies our water derives 2/3 of its supply by abstracting it from the chalk aquifer below us. The extent of that abstraction and the location of the abstraction points has been impacting our rivers for decades, resulting in our situation where the upper reaches are dry for most of the year, running predominantly as drainage ditches in periods of inclement weather.
Obtaining all the figures on the historic levels of abstraction in the catchment has not yet been possible, though we have been able to source the following from Affinity which gets us back to 1995.
I was also able to source information from the Chalk Stream Restoration Strategy appendices, which has been most helpful in understanding the abstraction picture across Hertfordshire and how levels of abstraction vary widely in different places.
The tables below consider each of the chalk streams of Hertfordshire in turn. Some of the figures and their origin need a small amount of explanation, for which I will use the River Ver that runs through St Albans in the Colne catchment as an example. The Ver catchment is 132km2 in area and receives 193mm of rainfall per year. These two figures are used to derive an average recharge figure, which represents the amount of the rain that falls in the catchment that ultimately reaches the aquifer, measured in millions of litres per day. The next column gives a percentage figure of the amount of that recharge volume that was then abstracted in the catchment by the water company – A%R. This is followed by the reduction in abstraction water volume (in millions of litres per day) required to achieve a target of abstracting a maximum of 10% of the average recharge, which is generally accepted as the upper level of acceptable abstraction to achieve good environmental status. The final column is one we have added and contains the population of the largest town in each catchment, sourced from the 2011 UK census. It is not therefore by any means an accurate representation of the population of each catchment, but I do suspect that it might be indicative of the geographic spread of Hertfordshire’s population and has at least some value in lieu of accurate catchment specific population figures.
|Stort||159||136Ml/d||18%||11.5Ml/d||Bishop Stortford (37838)|
|Source: 2011 census|
To summarise this information to a soundbite, the Rib & Quin catchment is the third highest abstracted by A%R and yet has one of the lowest populated areas. We have on one side of us a river valley that is not abstracted at all, whilst on the other side our friends on the Beane still have an A%R of 40% despite achieving historic abstraction reductions.
So, having considered the three elements that make up the trinity of a healthy chalk stream, how do the River Rib and River Quin shape up?
Well, we know our general environment is still supporting some outstanding and biodiverse wildlife, from our nationally unique carex cespitosa to winter flocks of golden plover, glow-worms to bee orchids. We know our rivers contain many of the indicator species of a healthy chalk stream and are producing comparable Riverfly scores to other similar sites across Hertfordshire. We know we have Brown Trout spawning at multiple sites with most recently the centre of Standon being added to the list and we have lamprey on both the Rib and the Quin.
We have landowners engaging to improve stretches of our river and parish and town councils considering and implementing river improvement schemes.
But we also have problems. Pollution continues to blight the water quality of our rivers and we now have, through the work of The Rivers Trust, identified the level of raw sewage spills impacting our rivers in recent years. We also now know the extent of abstraction undertaken by Affinity Water in our catchment and how it compares with other areas.
So what next? Most immediately we should pursue answers to the questions below. They are all fair ones and deserve answers that give an indication that remedies to reduce the volume of spills and abstraction in our catchment are not just something our grandchildren might hope to see.