Dry Chilterns chalk streams - a simple but revolutionary solution

The ever growing population of the south east needs water, and so do our chalk streams which have been suffering from low flows and, particularly in the Chilterns, drying up, because of the demands placed on the chalk aquifers that supply both rivers and people.

In this blog, Charles Rangeley-Wilson describes a simple but revolutionary solution to the problem. Take the water from the lowest reaches of the river, not the top. Chalk-Streams First has the potential to completely re-naturalise the flows in all of the Chilterns chalk-streams with potentially only a small net loss to overall public water supply. 

Charles Rangeley-Wilson is Vice President of the WTT and one our founders. 

It’s high time we put Chalk-Streams First

Ten years ago, I worked on a campaign with WWF focussing on the terrible impact of abstraction in English chalk-streams. We called it Rivers on the Edge, because they were … on the edge of survival. In a speech on the banks of the River Mimram in heart of the Chilterns I highlighted how locals there and on the neighbouring River Beane had been protesting about their drying rivers for at least twenty years. They still are. For too long it’s been Groundhog Day with our over-abstracted chalk-streams. But finally, we may just dare to hope that we can fix this problem once and for all, at least in the Chilterns.

It’s high time we did.

Chalk-streams are paradisiacal rivers. Their qualities of clear, cool water, equable flows, and abundant wildlife all derive from that qualifying word, chalk. We all know it from black-boards. Chalk is common enough geologically too: there are great swathes of it across eastern Europe. But the unique way in which the English chalk lies at the surface and was worn away but not completely worn away by the last Ice Age has given us eight-tenths of the global total of the rivers we know as true chalk-streams. The remainder are found over the channel in northern France. 

That’s some natural heritage. The unspoilt chalk-stream is a watery Garden of Eden. With their chequered beds of water crowfoot swaying in the marbled currents, their banks decked out in a bunting of marsh marigolds, water mint, and flag iris, they are utterly beautiful in a way that almost defines the southern English countryside. Chalk-streams are rich in wildlife too: under the surface there are brown trout and grayling, white-clawed crayfish, freshwater shrimp and all sorts of darting insects; in and over the plashy meadows there are snipe and otters, water voles and mayflies. Chalk-streams are an English Okavango, an English Great Barrier Reef, an English rainforest. 

Which ought to mean we should value this heritage as highly as we would any other globally-unique eco-system.

Sadly, we don’t. Or we haven’t. Instead these unique rivers are too often abused: some to the extent that they have dried up and ceased to be rivers at all. In May 2017 WWF commissioned me to take photographs of the same Chilterns chalk-streams we had mourned in 2010 … what was left of them at least. They were dry (again) or hardly flowing at a time of year when chalk-streams are usually at the fullest. The worst I’d ever seen. The rivers were dry, or mere trickles, far downstream of their winterbourne headwaters, far downstream of ancient mills, and old market towns and ​“No Fishing” signs and even Environment Agency flow-gauging weirs. 

In spite of, or perhaps because of, how bad it got in 2017 we can at least say that some progress has been made: no-one is denying there’s a problem anymore. No-one is questioning the link between abstraction and drying chalk-streams or suggesting that further research is needed before we can be sure. There have even been some moves to lessen abstraction. 

But the real problem at the heart of all this is that southern England is full of people and and water is scarce. The Water Companies have an obligation to supply water to the public. They have a right to abstract it, and although nowadays the Environment Agency has the power to revoke licences they deem to be environmentally damaging, in reality alternatives to the water in the chalk aquifer are very difficult and expensive to realise. So, for year after year we make incremental progress without ever fixing the problem.

Until now?

A new idea called Chalk-Streams First has the potential to completely re-naturalise the flows in all of the Chilterns chalk-streams with potentially only a small net loss to overall public water supply. It is a scheme that could be delivered in the near future using as its basis infrastructure that is already planned for and costed in the water company management plans.

Chalk-Streams First is supported by a coalition of The Rivers Trust, The Angling Trust, WWF UK, Salmon & Trout Conservation and The Wild Trout Trust and we are calling for the idea to be included in OFWAT’s multi-million pound strategic review of water resources across the south east.

Thus far the proposal has been independently reviewed by expert hydrological engineer Colin Fenn whose key conclusion was …

“ … that the draft Chalk-Streams First proposition, as put, identifies a feasible and a viable solution to the problem of chronic flow depletion in the internationally-rare and precious chalk-streams of the Chiltern Hills; it being to allow flows in the upstream chalk-streams of the Chilterns to run unreduced by abstraction, with water being taken from the correspondingly enhanced flows in the downstream Colne and Lee, and as needs may be from a range of other less-environmentally fragile sources to meet the needs of demand centres in the Chilterns, using Affinity Water’s already planned ​‘Supply 2040 scheme.”

There is a link to the report at the end of this blog.

The Chalk-Streams First coalition is calling for an urgent, and detailed and fully independent investigation of the idea as part of OFWAT’s strategic investigation of water resources across the South East England.

It’s high time we put Chalk-Streams First.

How Chalk-Streams First Works

If Chalk-Streams First sounds too good to be true, it is also relatively easy to explain how it works. First you need to understand the relationship between the level of the underground body of water — the aquifer – and the flow in the river. It is both a very complex relationship – there are all sorts of nuances and no two valleys are the same – and yet a rather simple one which can boiled down to: the higher the groundwater, the higher the flow in the chalk-stream. There’s even an equation that is remarkably accurate across many streams: a 10% increase in the groundwater level equates to a 25% increase in the river flow. And as the groundwater level increases, so the chalk-stream rises further and further up the valley.

To illustrate it, let’s see the chalk aquifer and chalk-stream as a bucket with holes up the sides. Those holes up the sides represent the length of the river: the highest few holes are the winterbourne headwaters, and below them are the middle and lower reaches down to the bottom of the bucket. 

The bucket itself is the chalk aquifer. Now we can fill the bucket with a hose: the water coming out of the hose is rainfall. The water spilling out through the holes: that’s the river flow. If we turn the tap up really hard so that the bucket starts to fill: that’s the winter recharge period. If we turn the tap down so that the bucket starts to empty: that’s the summer discharge period. 

The real chalk aquifer rises and falls seasonally, just like this simplified model. Aquifers fill in the winter when inflow tends to exceed outflow (even if the main natural outflow is the river, a real chalk-stream valley has other forms of natural outflow … transpiration and evaporation and some movement of water through the chalk underground) and discharge over the summer months, reaching a low point in early autumn, before the winter re-charge period begins. Winter rainfall is key therefore: the chart below from the River Tarrant shows how important winter rainfall is for the replenishing of groundwater levels.

The real chalk-stream flows like this too. The flow increases as the bucket fills: just as the river flow increases as the groundwater builds in winter. The river (represented by the holes up the side) gets longer, too. And then as we turn the tap down through ​‘the summer’ the holes at the top falter to a trickle and then one by one they stop altogether as the water level drops further. That’s the upper reaches of the river drying up and the overall flow decreasing, seasonally.

Notice how the water spurts farthest from the holes lower down the bucket and also as the level in the bucket falls during the summer discharge the flow from all the holes added together diminishes too. That’s because the flow rate is a response to the hydrostatic pressure in the bucket. The lower the level, the lower the flow: just like in a real chalk-stream.

Now to see the impact of abstraction … let’s set the tap so that all the holes are flowing and the water coming in from the hose matches the water going out through the holes. 

Then let’s drill another hole in the side of the bucket and create a new outflow that represents abstraction, with some of the water going in a different direction towards ​“public water supply”.

As soon as that hole is tapped, the bucket will start to empty until it reaches a new state of equilibrium at a lower level: that is the impact of abstraction. The new abstraction hole has supplanted the top three river holes (shortened the river) and it has lessened the flow in all the others.

It’s very simple: what goes in goes out. Under natural conditions it goes out down the river (plus the transpiration and evaporation I have mentioned). Under the unnatural conditions of an additional out-flow called ​“abstraction” the flow in the river diminishes: in this case by the exact amount abstracted, in the real world by an amount that is proportional to but not quite the exact amount abstracted (because of the other forms of outflow).

It stands to reason therefore that if we stop abstracting – or in this case put a bung in the ​“abstraction” hole in the bucket – the aquifer level will rebound and the river will eventually recover to the same level it was at before the abstraction. This is called ​“flow recovery” and it is the key idea behind Chalk-Streams First. 

Detailed modelling of flow recovery in chalk-streams in Dorset (the River Tarrant) and Berkshire (the Kennet) – both slope-face streams similar to the Chilterns rivers – suggests that for every unit not abstracted from the groundwater in the upper valley, approximately 80 to 85% of that unit will become surface flow in the river. 

So …. Let’s stop taking water from the aquifer. Let’s allow it to flow down the chalk-streams. Then let’s take it from the lower end of the catchment instead, after the chalk-streams (and the fish, birds, plants and insects) have had use of it first.

Hence we have called the scheme Chalk-Streams First.

Chalk-Streams First very simply makes use of the way chalk-streams function by moving the point of abstraction from the groundwater at the top of the valley, to the surface water at the bottom of the catchment where it can be taken into storage in the big reservoirs around London.

The obvious question which follows this simple idea is, how do we provide water to those towns formerly supplied by the groundwater, when all the water is now downhill at the bottom of the Rivers Colne and Lea?

The answer is a pipeline scheme called ​“SUPPLY 2040” which is already included in Affinity Water’s business plan. Affinity Water plans to build this pipeline (in fact a development and reinforcement of existing infrastructure with additional components and sections) anyway, to move water from their own excess zone south of the Thames to the deficit zone in the north. It is also needed for many other strategic infrastructure schemes currently under consideration, including Abingdon Reservoir and other options.

SUPPLY 2040 would enable the water that has been liberated to flow down the chalk-streams (or its equivalent volume) back up to the towns currently supplied directly from the groundwater. Better still SUPPLY 2040 could relatively easily be shifted forward to become SUPPLY 2030, meaning the re-naturalisation of all the Chilterns chalk-streams is within reach in less than ten years.

What we need now is a really detailed, independent investigation of the viability of the scheme. The Chalk-Streams First coalition has asked RAPID to run that investigation (RAPID has been set up by OFWAT to administer the strategic review of water resources). So far, the reception of the idea has been really encouraging.

But the more this scheme is talked about, the better. We need it out there in the conversation. If Chalk-Streams First can work in the Chilterns it could eventually become a model for how we save other chalk-streams in the future.

It’s high time we put Chalk-Streams First.

To read the proposal click HERE.