chalk streams – Page 2 – Chalk-Streams

The counter-intuitive (and heretical) idea that could unlock abstraction reduction.

February 8, 2025February 9, 2025Posted in UncategorizedTagged chalk streams, climate-change, environment, groundwater, sustainability, water1 Comment

It took me a while to get my head around the concepts in this post, so bear with me. This is aimed especially at eNGOs and other campaigners for chalk streams, because the more people there are who understand this counter-intuitve idea, the better.

Here it is: you can save many chalk streams from unsustainable abstraction by conceivably using the aquifer in times of low flows and drought.

That is a head-muddler. But this idea could unlock real abstraction reduction, making the bad much better in the foreseeable future. This is far, far preferable in my view than holding out for a perfection (natural aquifers) that will never come.

It starts with my best attempt at explaining what I understand of the complexities of the interactions between groundwater, river flow and groundwater abstraction. Given that I vainly spent a long night in a hut in Iceland trying to explain the very same ideas to two angling friends of mine (they were belligerently uncomprehending in a (successful) effort to annoy me), this will be no easy task.

It is complex … kind of. It’s also quite simple really. Rather as the moon affects the tides, a simple idea leads to a complex set of manifestations.

Idea 1. Chalk streams flow from underground.

If you’re reading this blog you’ll already know that chalk streams derive most of their flow from groundwater. Rain sinks into the ground filling fractures in the underlying chalk and then lower down the slope it seeps out again as springs to create a chalk stream.

Idea 2. The level of the groundwater drives the flow in the river.

This is pretty simple. I used the bucket analogy before. Drill a single hole in the base of a bucket. Fill the bucket with water. As the bucket fills gravity drives water at an increasing velocity out of the hole. Now stop filling and let it empty. The flow diminishes to a trickle. EVERYONE gets this because it’s the same when you pee!

*The rate of flow from springs in a chalk valley is driven by the hydraulic head of the groundwater above the springs. The higher the level, the greater the flow* …

*… In more or less the same way as the water level in the bucket determines the force at which the water is driven through holes in the side of the bucket.*

Idea 3. Groundwater rises in winter and falls in summer.

If you pour water into the bucket faster than water can leave it through the hole(s), the level in the bucket rises. If you stop pouring water in, the level falls as the bucket drains. This is exactly the same with a chalk aquifer. In winter, when it rains a lot, and it’s cold and the ground is wet and nothing is growing, more rain flows into the aquifer than can leave it and so the groundwater level rises. In summer, much less rain – if any – reaches the aquifer and so the groundwater level falls.

*Groundwater rising. This chalk valley is dry most of the time but in February 2021 when recharge vastly exceeded discharge, it had filled to overflowing*.

Idea 4. The higher the groundwater rises up the valley, the more the water pours out of it.

As groundwater level rises, stream flow increases. But not in a linear way as it would with a single hole at the base of a columnar bucket. In fact for every unit of rise in groundwater level, flow will increase by approximately X^{2 to 2.5}. Kind of like having twice as many holes at each level in the bucket as the level below.

There are a number of reasons for this which were debated at a recent groundwater conference. There is a summary of these ideas in Section 2 of John Lawson’s report Flow Recovery Following Abstraction Reduction which we updated following the conference and contributions from the likes of Rob Soley and Alessandro Marsili.

In short, this non-linear response is probably caused by a combination of:

• the shape of the valley – if you imagine the groundwater filling the valley bottom and hillsides, assuming a perfect V- shape valley, for every unit increase the groundwater rises the area of saturated zone exposing springs rises two-and-a-half fold. Chalk valleys are not quite V-shaped but that’s the general idea.

• the fracture density in the chalk – which increases in the valley bottoms and with altitude. At depth chalk is very solid, but in the valley bottoms and higher up the slope and where water has flowed for thousands of years, the fracture density is much greater and the flow pathways are bigger.

• layering within the chalk – chalk accreted in layers under varying climatic / geological conditions and these layers are in turn interrupted by bands of clay and flint. These layers and the varying permeability and transmissivity can influence the way groundwater reaches with the surface.

• as the surface flow pathways lengthen (winterbournes rising higher and higher up the valley) the groundwater pathways shorten.

The fracture density and layering in the chalk, the shape of the valley and the length of flow pathways, all conspire to mean that when chalk valleys fill, flows will rise exponentially.

Idea 5. The impact of a constant groundwater abstraction has a varying impact on varying flows through the year

This is where things gets a bit more discombobulating. All of the above essentially means that as groundwater rises, flows increase exponentially. If that is true, then the reverse is true. For every unit of decrease in groundwater level, flows decrease exponentially.

This means …. drum roll … groundwater abstraction (which lowers groundwater levels) has a greater impact on high flows than low flows! This is a totally skull-tightening idea. Everyone thinks the reverse must be true. But it isn’t.

Groundwater levels and groundwater abstraction

Let’s start with the impact of groundwater abstraction on groundwater levels. In a natural aquifer system, the discharge from the valley must equal the recharge over time. Natural recharge = natural discharge / Time. This stands to reason: if it didn’t the valley would either fill to overflowing or empty (because over time one would exceed the other).

Natural recharge derives from rain and natural discharge from river flow (and some evapotranspiration and flow through the ground). If I add another form of discharge in the form of abstraction, then the former natural discharge MUST go down. If it didn’t, the aquifer would progressively empty until there was no water left (an aside … hydrogeological literature generally describes anything less than draining the aquifer “sustainable”, because the aquifer is being lowered to a new dynamic balance, not mined. This is not the same as ecologically sustainable, however).

Look at it as simple numbers.

Natural recharge (10) = natural discharge (10) / Time.

Natural recharge (10) = abstraction (5) + natural discharge ? / Time.

What’s the new natural discharge? 5, obviously.

Now, as I showed with the bucket, the ONLY way in which the former natural discharge can go down is through a reduction in groundwater levels. If groundwater levels didn’t go down, then because the discharge is driven by the groundwater level the natural discharge would remain the same. As shown above, that is impossible.

Theis, the Isaac Newton of groundwater theory, wrote all this in 1940. The only way that the former natural discharge can go down (and balance the equation) he wrote, is by a reduction in the “thickness of the aquifer”.

Okay, so pause and get your head round all that.

• a single unit of rise or fall in groundwater level has a (very roughly) two-and-a-half fold impact on flows.

• groundwater abstraction lowers groundwater levels.

• ipso facto a single unit of reduction in groundwater level at high groundwater levels has a much greater impact on flows than a single unit of reduction in groundwater level at low groundwater levels.

It still hurts the head, but the discombobulating stuff above means that at high groundwater levels groundwater abstraction reduces flows by quite a lot more than 100% of the amount abstracted. And conversely, at low groundwater levels groundwater abstraction reduces flows by quite a lot less than 100% of the amount abstracted. Albeit over time groundwater abstraction must reduce flows by (essentially) 100% of the amount abstracted (it’s generally less than that for reasons that aren’t that important to the general concept, but basically because not all discharge occurs in the form of flow).

See the chart below to see what the Chalk Streams First modelling indicates % flow recovery would be if abstraction was reduced to zero in the River Ver. It varies through the flow cycle.

The above chart from Page 52 of John Lawson’s report shows that the % flow recovery (green line) at high flows (l/h end of X axis) is well over 100% and at very low flows (r/h end of X axis) is about 30% – 20%.

Idea 6. Groundwater abstraction at low flows is like a credit card.

The obvious question is … if groundwater abstraction at low flows reduces those flows by a lot less than 100% of the amount being abstracted, where the bloody hell is the rest of the water coming from? The answer: if it’s not a direct reduction from flows at the time, it is coming from aquifer storage.

This is easy to understand if you think of a large abstraction next to a small and diminishing stream. In the winter when the stream is gushing, there is more than enough water to satisfy the pumping. In the summer the stream reduces to a trickle or perhaps even dries up. But the pumping continues. At this point the abstraction is clearly not taking water from stream flow because there isn’t any. Another aside … I’ve read hydrogeologists describe this state as abstraction having “no further effect on flows”. This might be literally correct at the time. But it is misleading. The abstraction is effecting future flows.

When a chalk stream dries but abstraction continues it is clear that the abstraction is no longer subtracting water from the river’s flow, but from aquifer storage: this is basically a debt to future flows.

At times of low flow and into droughts, groundwater abstraction increasingly draws on storage, upon which future flows are built. If you unnaturally drain the aquifer, it will clearly take longer to fill when it starts raining again, all before the flows in the river can respond to the rise in groundwater levels.

Therefore groundwater abstraction at low flows is like a credit card: much more a debt against future flows than an impact on present flows. This is a key idea behind the confusing concept of using groundwater abstraction to unlock abstraction reduction .

Idea 7. If you turn off the pumps you get greater flow recovery at high flows than low flows.

Essentially what all this means is that when you cease or lower abstraction you get well over 100% of the amount no longer abstracted at high flows and much less than 100% at low flows. That is what the chart above shows on the River Ver.

And this is the Achilles Heel of the Chalk Streams First idea.

Water resources needs a constant supply of water. Groundwater abstraction gives that. Chalk Streams First says “turn off (or down) the pumps and take the water from river flows much lower down the catchment”. And while you get loads of water back in winter, you get less back in summer. Generally, you must have a storage reservoir to make it work and balance out the varying recovery rates into a constant and reliable supply.

John Lawson – who came up with the Chalk Streams First idea – has long known this. We argue (with empirical evidence) that the flow recovery at low flows is actually much higher than the most pessimistic predictions claim, but nevertheless this variation in response is an issue we have to address. The answer is a reservoir.

BUT … then you get to the prolonged droughts when water companies are under real pressure. In these times, the flow recovery could conceivably drop even lower. What to do? The public must have water. This low flow recovery at very low flows in long droughts threatens the whole idea of reducing abstraction through schemes like Chalk Streams First. Especially now that we have to plan according to 1:500 year contingencies.

Idea 7. In droughts use groundwater abstraction to guarantee public water supply … so long as you’ve turned the abstraction right down to ecologically sustainable levels 95% of the time.

The insurance against the Achilles Heel of low flow recovery in a drought is a groundwater-fed public water supply scheme. There is one in existence already called the West Berkshire Groundwater Scheme (WBGWS). It is a series of wells in the Berkshire chalk that can, in extremis, be turned on and deliver a large amount of aquifer water into the Berkshire chalk streams, from where it flows to the Thames to be captured into the London reservoirs. The scheme is used very, very rarely: no more than once every 25 years. But it’s there. And it guarantees water in a drought.

The West Berkshire Groundwater Scheme wellfield: this scheme is rarely used but guarantees water in extreme droughts. It is a counter-intuitive idea that could unlock abstraction reduction in the Colne, Lea and Ouse chalk streams.

The impacts on the chalk streams are a) one of flow relief in the drought, because the flows get boosted. Albeit – and I have to emphasise this – flow augmentation in not the aim of the scheme, it is a bi-product. And b) at the end of the drought, when the pumps are turned off, the aquifer must recover before flows return to natural levels, so you get lower flows the following year.

But this is crucial: in modelled scenarios, the flows in the year of recovery are still better than they would be if abstraction ran all the time as happens at the moment in streams like the Ver, Misbourne and Beane.

So WBGWS type schemes could unlock Chalk Streams First type abstraction reduction in other settings, such as on the chalk streams of the Colne, Lea and Ouse (even the Darent). As such a scheme would insure against the public supply deficit in droughts created by replacing upper catchment groundwater abstraction with lower catchment surface water abstraction (the Chalk Streams First concept).

BUT …the Environment Agency is very cautious of such schemes

This is understandable because there have been some bad schemes in the past. But flow augmentation to compensate for the collateral damage of abstraction is a different thing altogether.

Some schemes were developed in the past whereby to compensate for abstraction (which had dried the stream) water was pumped from the aquifer into a losing reach of stream and the whole thing was a highway to nowhere.

Other times the concept of augmentation is used to justify continuing, unsustainable abstraction. These schemes have given the whole idea of flow augmentation a bad rap, and one that has stuck like glue.

RevIvel claim that a flow augmentation scheme putting 0.5 ml/d into a dry river bed is not a good type of augmentation scheme, especially if it delays a proper solution to the unsustainable abstraction. This is the kind of scheme is very different from the idea promoted in this blog post.

BUT, I would argue that we need to be more pragmatic and open minded than a presumption against these schemes if we are to achieve the heretofore irreconcilable goals of reliable public water supply and restored chalk streams. Aquifers in the south east are managed one way or another. We need to make sure they are managed mindfully to achieve the specific outcomes we want and in this regard holding out for “natural” when a more flexible approach would unstick hopeful schemes such as Chalk Streams First would surely be counter-productive?

I understand the Environment Agency may be consulting on this topic later in the year. I know from many discussions I have had with chalk stream advocates that the ideas I have outlined above will be surprising and counter-intuitive to most of us, as indeed they are to me.

But it is vital we give the EA the encouragement to take a flexible, if ultra cautious approach, because the gains of doing so could be massive.

Prioritising abstraction reduction: we need common sense more than we need evidence.

November 20, 2024November 20, 2024Posted in UncategorizedTagged abstraction, biodiversity, chalk streams, ecology, environment1 Comment

It’s brilliant that the Environment Agency has, through the national framework, identified the flow deficits that exist on our chalk streams.

It’s great that Environment Agency has signalled to the national framework groups that chalk streams should become a priority in terms of addressing those deficits.

Thus far, however, the Environment Agency has inclined to stand back – at least publicly – from guiding the decision-making that will be needed to apportion those abstraction reductions strategically and cost-effectively over time. This is being left to regional groups and partnerships, but it is not yet clear how these decisions will actually be made or if they will be consistent and logical.

Our CaBA chalk stream strategy called for the collaborative development of a prioritisation process and while everyone agrees the need, it still hasn’t quite happened.

In all of the meetings I have ever attended in which abstraction reduction is discussed the idea is aired that we will need evidence to justify and ensure wise decision-making, including evidence that ecological gains will follow mooted abstraction reductions.

On the face of it, the call for evidence seems only prudent and sensible – after all public money is at stake.

But the idea that such evidence could ever exist is a chimera.

Clear cause-and-effect evidence according to a robust, before / after / control / impact method of proof, is – I argue – impossible to acquire. And it is so, precisely because of the infinitely complex web of cause and effect that is leant upon to justify the call for evidence.

Water companies will argue, and rightly, that reducing abstraction is expensive and, therefore, that there’s no point doing it if no benefit follows. Or if the potential benefit is neutered by some other factor such as a heavily modified river channel, or pollution from farms. In certain settings we run a real danger of spending millions reducing abstraction, when other factors – like the fact that the river is navigable and impounded by locks and weirs – are as big or even a bigger brake on the ecological health of the system from which there is no possible relief.

There are also settings where the cost of reducing (some of) the abstraction could be more cost-effectively spent (in terms of ecological gain per buck) improving the physical habitat. We have transformed canal-like channels in Norfolk into vibrant, wild and free-flowing streams for modest amounts of money, all things considered. £200,000 per km is dwarfed by the £4 million cost of replacing 1Ml/d of water. For that you could rebuild 20 km of knackered chalk stream.

I’m all for the intelligent and undogmatic trade-offs and counter-intuitive thinking that will be needed if we really are to balance the needs of society and nature.

But the call for evidence is self-deluding at best and a delaying tactic at worst.

Why?

In the insanely busy and pressured landscapes we are talking about it is virtually impossible to strip out the variables: the physical condition of the channel; the micro and macro stressors of water quality which are highly complex and some of which we barely understand; shifts in the global agricultural markets which might generate or ease an agricultural pressure beyond one’s control or easy quantification; road run-off which might be terrible in a year when a local farmer is rearing pigs, or not too bad when the farmer gets rid of the pigs or in a mild, dry winter; the weather; the climate; the impact of invasive species like signal crayfish, or predation from cormorants when a cold winter forces them off the reservoirs: etc. etc. etc.

I defy anyone to design an experiment into the teeth of those variables, that could possibly isolate the beneficial or non-beneficial impacts over time of one single action.

The only way you could construct such an experiment would be to select a stream where abstraction is pretty much the only pressure and a significant one, gather baseline data for at least five years, ideally a decade and then COMPLETELY TURN OFF THE ABSTRACTION in that stream and all nearby streams (because you need the signal to be significant to rise above the variables you can’t eliminate no matter how hard you try) and study for another five to ten years. The study periods would have to either equally include or exclude periods of drought and very wet years too.

When helping to write Defra’s now scandalously abandoned chalk stream recovery pack, I was looking for exemplar case studies of where abstraction reduction had made a significant and demonstrable beneficial impact to ecology. I struggled to find a slam-dunk example, mostly because the reductions that have been made – though significant – have been made from very high totals and are actually quite small against the volumes still abstracted. For example, on the River Ver, while abstraction once exceeded 50% of recharge, it is still 30% of recharge.

This reach of the River Piddle used to dry regularly in the late 1980s early 1990s.

I cited the River Piddle in the end, even though the changes made there since the dark days of the late 20thC when the river dried up regularly, include flow augmentation as much as abstraction reduction. The Piddle, however, is indeed much better now than in 1989 – 93. I know because I’m lucky enough to co-own the bit that used to dry up and it is now an exemplar of chalk stream health. It is an example.

But even so, water companies and others will often say abstraction reductions made thus far haven’t yielded the hoped-for results. Either in terms of flow or clear ecological gains.

In terms of flows, this is not true. John Lawson’s analysis of the flow-recovery following abstraction reductions shows unarguably that flows do recover in proportion to abstraction reduction. But when the abstraction is really high and you only reduce it a bit … hmmm.

John’s report also shows that the reductions made, though significant and expensive in water resource terms, have been far too small relative to the size of the overall catchment abstraction and far too small to rise above the “noise” made by all the other variables (and many of these variables haven’t been attended to properly, either. We still have a lot to learn about high-quality and cost-effective process-based habitat restoration).

In the only really good long-term BACI type flow scenario that exists, flows on the River Ver reduced and then recovered exactly in sync with the abstraction increase and then reduction. Of course they did: where else would the water have gone to?

So, if slam-dunk cause and effect evidence that reducing abstraction Y will lead to X ecological recovery doesn’t exist and can’t be found, how do we approach the problem?

Without knocking the idea that data and evidence are useful tools to guide our decision-making, we should not abdicate our own common sense. In the same way that we don’t need science to tell us that it’s warmer in summer (though we need science it to tell us why) we don’t need science to tell us that abstraction adversely impacts the ecology of a river (though we do need it to tell us why).

Many fine minds have spent a lot of time discussing and agreeing that sustainable abstraction in chalk streams should generally cause less than a 10% reduction in natural low flows, (which also, give or take, amounts to 10% or less of the average aquifer recharge). That is why we have the Environment Agency’s Environmental Flow Indicator, which is based on the UK Technical Advisory Groups deliberations on exactly this flow / ecology balancing act.

What we need beyond this work (that has already been done!) is not so much more impossible-to-find evidence but rather a screening process that aids and brings logic, common sense and consistency to the thorny issue of how to spend public money most cost-effectively in our collective goal of achieving sustainable abstraction on chalk streams.

To give a really obvious example: we need a screening process that stops us spending billions of pounds reducing abstraction in a river that is navigable and therefore doesn’t really have a flow-dependent ecology, but compels us to crack on with spending millions of pounds reducing abstraction in iconic chalk streams which can also be physically restored for 200k per km!

That really shouldn’t be too difficult.

I have made a start below … comments welcome.

Screening flow-chart for abstraction reduction prioritisation Download

The ‘shocking’ State of England’s Chalk-Streams 2014

November 26, 2014January 6, 2017Posted in chalk streams, conservation, events, river restorationTagged chalk streams, ecological restoration, WWF6 Comments

_dsf3142 — England’s chalk-streams: their shocking state is the ecological restoration opportunity of our time.

Last night I was invited to speak at the launch of WWF’s new report: The State of England’s Chalk Streams 2014. The report reveals that over three-quarters of these iconic and globally unique rivers are failing to meet targets for ecological health. This is what I said to the audience at the South Bank Centre:

“I want to talk to you this evening about how the state of England’s chalk-streams – a state this new WWF report correctly describes as shocking – could become the most incredible opportunity for ecological restoration. We have the means and we have the knowledge to rehabilitate this broken ecosystem. All we lack is the will. But will is only a change of mindset. Minds can be changed.

In some ways this ‘shocking state’ is not surprising.

I’ve just spent five years researching a book looking for the reasons why, in 1965, a chalk-stream in Buckinghamshire called the River Wye was buried under the streets of the town it gave life to. The answers were on one level mundane and soulless: the river was buried to widen a road. On another they were as complex and layered as the history of the valley that river flowed through. Geology and industry and slum clearance and town planning stacked up one after the other, until the river’s burial became as inevitable as the construction of a shopping centre above it: a retail cathedral which the Council named Eden.

The world over the struggle between nature and man, between the stream and the street, ends with the incarceration of the stream. It’s not that anyone especially means rivers any harm. It’s just that through an ironic twist of history rivers give birth to and then get in the way of economic expansion. Swap street for field, the principle holds.

English chalk-streams flow through landscape at the epi-centre of Western civilisation: certainly in terms of the depth of its history, the density of its use. In other words, they are a globally unique eco-system in the very hottest part of the fire. Of course they’ve been pushed to the edge of existence. Looked at this way, it is a minor miracle that we have any chalk-streams left at all.

That river was buried to widen a road. It is worth remembering that this is how it happens. No-one is planning or hoping for a world in which there is no room for nature. But the end of the wet and the wild is death by a thousand cuts: none of them is actually mendacious, but all of them are careless.

And yet, this grim fact is also an exciting opportunity. If economic growth almost always leads to ecological destruction, it doesn’t have to. Making room for nature begins with seeing how it matters. So why do chalk-streams matter? Why should we care more? I can try to tell you why I care.

I grew up in London, but every other Friday night through the late 1960s and then the 1970s we drove north to spend the weekends in Norfolk. I had no particular idea then, as I struggled to peer out the car window, that the route we took, around the edge of the Chilterns, across the Hertfordshire downs, up the ridge of the Gog Magog hills all the way to the multi-coloured cliffs of Hunstanton, was more or less entirely across a chalk landscape. But towards the end of the journey, when the evenings were long in summer I would ask my father to slow down over one or other of the bridges which crossed the streams near our house. One was over a river called the Ingol, where it tumbled over a small waterfall beside a bus stop. Another was over an equally small stream called the Babingley. I adored these miniature brooks for a reason I could never have explained. They just spoke to me and I loved to spend a few moments watching them flow.

Now, forty years on, I know that these little brooks were chalk streams. I also know that we would have crossed others on that journey: the Colne outside Heathrow, and then that river’s Chilterns tributaries the Chess, Misbourne, Gade and Ver. Running north up the A1 we would have crossed the Lea and the Mimram and then, riding the ridges of those chalk hills we threaded between the Beane, Oughton and Purwell. Turning east we narrowly missed a few more – the Cat Ditch, the Ivel, the Hiz – before we crossed the Cam and then the Granta. Further on we crossed the Snail and then the Fenland incarnation of the Lark. Then the Little Ouse, the Wissey, the Nar, and finally, nearing home, we crossed the Babingley, the Ingol, the Heacham and smallest of all, the Hun.

Those 24 names represent a good proportion of all the chalk-streams that exist globally: about one-eighth of those in England, whose total of a little over 200 streams – varying in size from the stately River Test in Hampshire, to diminutive little brooks you can almost hop over – make up most of the chalk-streams in the world. There are a number of chalk-streams over the channel in Normandy. But further afield, although there are great swathes of chalk across Kaliningrad, Bulgaria, Czechoslovakia, or the Ukraine, although there is chalk in Texas, Israel, Egypt and Australia, it seems that there just aren’t any rivers like the English chalk-streams. Ours appear to be almost unique.

To understand why you need to think of Europe as … well if you’re into cooking think of a layered cake and if you’re into DIY think of plywood. I’ll go with the cake metaphor …

… the chalk is just one layer, the white sponge say, sandwiched between layers above and below. Now, imagine you tilt the cake so the layers no longer lie flat. Now, squeeze it from each side so the whole cake buckles. Finally take a knife. This knife is made of time and ice and rain and wind. Run the knife across the top of the cake: but don’t be too careful about taking a neat, even slice. The knife, you’ll find, slips more easily through the softer layers, the cream, the fluffy sponge; but it struggles a bit at the toffee and caramel. It all gets a bit messy of course: the cake you have cut away, some of it dissolves, while some of it is spread across the surface elsewhere. This layered, tilted, buckled and untidily sliced cake that you have imagined is the surface of the earth. The layers of rock, the layers of the cake, show at the surface in bands. In places the bands are smeared over with the remnants of other layers. In places they stand clear. The layer of white chalk at the surface in the Chilterns, for example, has been cut away and is long since gone from over Scotland; it lies intact but deep under the surface of eastern France; and in Bulgaria, while it might be more or less at the surface, it is covered with great smears of other stuff.

This is why most chalk-streams are English. Chalk-streams only flow where that soft, soluble white rock protudes at the surface, and more to the point, where it is relatively uncorrupted by the marbled mess of depositions left behind by the knife.

And what is this chalk? It is the fossilised remains of infinitesimally small sea creatures which swarmed millions of years ago in pre-historic seas. Most of Europe was once under the sea. Chalk formed at its edges where countless billions of dead coccoliths rained down to the ocean floor, settling and compressing into a porridgy ooze, which became in time, chalk. It took a while: the chalk accreted at a rate of one millimetre a century, one centimetre every thousand years. And now we have our chalk hills: a great belt of them in England that runs from south-west Dorset, past London, through East Anglia and up into the Yorkshire Wolds. Some of these hills are hundreds of meters thick.

Chalk-streams, like most rivers, begin with rain. But when rain falls on chalk it sinks into the ground through fissures and cracks, or it soaks into the body of the chalk itself, turning the hills into underground oceans of trapped water. A drop of rain might travel five miles or 50 under the earth, it might stay down there five months or five years or five centuries. The subterranean topography that determines exactly where the water goes is immensely complex, almost unknowable.

What we do know is that here and there, in a wet furrow in a meadow, or under the roots of an ancient tree, or in a rook-filled copse on the edge of a hill, that water re-emerges as springs – and that in these special places chalk streams are born.

What flows from the spring is no longer plain rainwater, however. It is chalk-water: cold and clear, and rich in minerals. The steady flow of this cool, fertile water in meandering, gravelly channels creates spectacularly diverse ecosystems. The unspoilt chalk stream is like a watery Garden of Eden: chequered beds of water crowfoot swaying in the marbled currents, constellations of white flowers, vibrant green beards of starwort and clouds of water-parsnip; the banks decked in marsh marigolds, water mint, and flag iris; under the surface brown trout and grayling, young salmon and sea trout, white-clawed crayfish, freshwater shrimp; in and over the plashy meadows, snipe and otters, water voles and mayflies.

But chalk streams are special not just in their geological origins, and the wonderful ecosystems this creates. No river on Earth is as much a product of human as well as natural history. They are such gentle, malleable rivers. They have been harnessed and lived with for thousands of years, shaping and shaped by human history in one of the most used landscapes anywhere in the world. Think of the Roman villas, the mills, the medieval priories and holy houses, the castles, the ornate Palladian parks and gardens, the fisheries, the Georgian water meadows. All these things give chalk streams a distinct beauty that is not the same as the sublime, unpeopled beauty of craggy peaks and spouting waterfalls. Chalk streams are home-spun and life-giving. Chalk streams are pastoral. Chalk streams are living, flowing history.

This intersection of geology and geography, of climatic history and finally human history has created a unique type of river: Edenic, life-giving. Chalk-streams are an English Okavango Delta, 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. Instead these unique rivers are abused: some to the extent that they have dried up and ceased to be rivers at all. Others are rivers in so much as they have water in them, but in every other way they are changed. Some are buried underground. Most are polluted too. To our shame most of the really debilitating changes have occurred in the last 50 or 60 years. Before that time chalk-streams were certainly much-used river systems, but our relationship with these rivers was to a large degree symbiotic. Since 1946 a fatal combination of dredging, diffuse pollution and water abstraction has made it parasitic.

Today, the range of threats is diverse and most are difficult to overcome in a busy, valuable landscape which also supports farming and industry, people and businesses.

Difficult to overcome, but surely – given the value of these rivers – not impossible?

Remember that river which was buried to widen a road? Now, fifty years after it was lost to the world, the Town Council is planning to unearth it again. The change has come because they believe it is possible and can see reasons enough to want to. The river will bring back the heart of the town. Like the rock that made the river, history took that stream underground and has brought it to the surface again. All it takes is will. A change of mind. A different way of valuing things.

There are two ways to look at this struggle between man and nature, between environmental growth and ecological destruction. Either we sacrifice the places where we live and work and try to pickle the places we don’t: which won’t save them, by the way, because they too will shrink until there’s nothing left.

Or, we learn to make room for nature and create a world where unique eco-systems can exist alongside or even inside functioning, economically viable landscapes. It is that polar choice which makes the sobering state of the English chalk-stream the most tremendous opportunity. If we can make that room here – and I know we can – we set an example for the rest of the world. We create a beacon of hope.

If we can do this in this busiest of landscapes, we can do it anywhere.

If chalk-streams are our burning rainforest, it is up to us to put the fires out.”

Trees in Rivers

August 1, 2014June 6, 2017Posted in chalk streams, conservation, riversTagged chalk streams, featured, river restorationLeave a comment

Monday morning 4th August and the next phase in the restoration of a small Norfolk chalk-stream begins. 3.5 km in two months, all being well.

Last year we (the Norfolk Rivers Trust working with Cain BioEngineering) took on a similar length – 3.5 km of straight and over-wide channel and did our best to replicate in two months what would have taken hurricanes and beavers (if we had them) two hundred years. You’ll get the idea from these before and after pictures: we felled trees and used them to rebuild a more natural, meandering channel.

It sounds simple enough. But why bother? Over the centuries chalk streams have been straightened, deepened and widened: for milling, for navigation, to construct water-meadows (a 17th Century technique for boosting farm productivity by flooding the floodplain) or to make them into drains (a 20th century technique for boosting farm productivity by draining the floodplain). The cumulative impact of all this modification has been to change our chalk-streams from the naturally meandering rivers they once were into uniform, over-wide and over deep canals.

Using trees to rebuild the meandering, low-lying riverbanks that a chalk stream should flow within brings a host of improvements to the habitat and eco-system. In the restored channel the water flows more quickly. The swifter flows scour the bed of stream so that there is clean gravel instead of deep mud. The faster flows favour weeds like ranunculus and starwort which help maintain a cleaner river, and provide better habitat for fish and insects. Along the shallow, wet margins reeds and grasses flourish and these also provide habitat for insects, birds and mammals. Selectively felling trees helps too, especially in the sort of semi-commercial forestry that borders a lot of our rivers: the ideal is the dappled sunlight and shade you’d find in a natural, mature flood-plain wood.

Altogether this carefully choreographed imitation of a small hurricane can absolutely transform a chalk stream, as these photographs show. The changes illustrated here have taken less than a year to evolve. In five or ten years the woody banks will have disappeared beneath trapped silt and vegetation and flowing through the middle will be a smaller and much healthier river.