Fallen trees are valuable ecological engineers.

I’ve known this bit of river since I circled the entry in John Wilson’s Fishing in Norfolk. Definitely since before I could drive. I would cadge a lift there when my parents went to the open-air market in Fakenham. Early 1980s then, maybe even late 1970s. The river in those days, according to memory, was broad, tidy and fishless. My fly-angling skills were not that developed but I was handy with an upstream worm. And yet I never caught much more than a few dace. The trout Wilson had promised were very few and far between. Not so in more recent years: trout have been far more numerous.

There will be a number of correlations: water quality, no doubt, which will be generally better now that the Wensum is a Special Area of Conservation (SAC) and privileged by reasonably high standards of sewage processing. But the most significant correlation, I am certain, will relate to that word “tidy”. The river isn’t tidy anymore and therefore the trout have been allowed to thrive.

Back in those darker days of the late 1970s, with the Common Agricultural Policy at its economic height, the Wensum was dredged to destruction. And every time it reared its almost lifeless head off the canvas, it was dredged some more. To be honest, I was amazed the Wensum was ever designated an SAC, as a more physically ruined chalk stream you will not find. Trout find it hard to get along in a dredged, straightened and impounded river that is razed to its silty bed once a year.

But an SAC the Wensum became and perhaps partly for that reason, but mostly because the flood defence teams of the NRA/EA/IDB, have been far less zealous in the last couple of decades, the gentle-natured Wensum has been clambering back slowly, at least onto its knees, if not yet its feet. Trees have been left in the stream. Reeds have been allowed to encroach. The process of self-repair has started.

In fact, that process had contrasted intriguingly with the accelerated “repair” enacted in the name of river restoration on other parts of the stream. I have been watching, for example, the startling difference between the reach 100 yards below the sewage outfall in Fakenham (left-hand image below), where the riparian reeds have encroached on a gravel bar and recreated a natural, meandering channel, with the reach 200 yards below the old railway viaduct (right-hand image below), where a “riffle” (aka weir) made of outsized flints has been installed, impounding the river drastically, causing a massive drop-out of silt and bank to bank accumulation of burr-reed.

The lesson being, nature knows best.

Rather the reason why the likes of David Sear and others have been questioning so hard exactly what we mean by “river restoration”, especially when it comes to chalk streams. They are such gentle rivers: what we do to them stays done for many years. We ought to make sure we get it right, therefore. I certainly made sure we used the CaBA Chalk stream strategy to broadcast that message loud and clear: chalk stream restoration should be about the restoration or facilitation of natural process and not the imposition of arbitrary anthropogenic concepts of riverine form (many of which actually stall those processes as the pictures above show all too clearly).

That self-repair that I was talking about: it had all been happening in the reach between Fakenham Mill and the railway viaduct. The river, as I have suggested, was four decades or so along a successional journey that, in my best estimate, was due to take at least a century, if not longer. But it was at least on that journey.

The Wensum here has been – like all chalk streams – diverted away from its natural course, impounded (in the two spots where the railway crossed it), and very heavily dredged and incised. The picture above shows the existing course in red and the natural course in blue. A chalk stream stuck in this kind of physical prison (red course) will take many, many years to break free. But break free it must … eventually. It would be intriguing to find out exactly how long “eventually” takes. I had been watching the Wensum in this rural but municipal reach, hoping its public ownership (it is council water) meant that it might be left alone long enough, and that I might live long enough, to find out.

Trees help and gradient help. Luckily for the Wensum, in the upper half, where there are not that many riparian trees, the stream is quite steep and in the lower half, where it is incised and impounded, there are lots of trees. So, it had the keys to its jail.

To recover the river must either:

a) recreate a meandering form within its current course (as in the picture on the left in the sequence above), which it will do a bit more quickly if the gravel bed is reasonably intact and if there is gradient, or much more more slowly if it first has to restore the gravel bed that was removed or if there is very little gradient (gradient equals energy and energy determines speed of recovery). In truth, this side of another Ice-Age, a chalk stream will not truly recover a gravel bed on the channel pathway from which the gravel has been removed: the best the stream can do in situ is blow out its banks and throw more gravel into the system, or fill up with silts and fine sands.

or it can

b) break out of its channelised, impounded and dredged course and carve a new pathway across the flood-plain, where there will be gravel that hasn’t been removed by dredging or find its way back to the original channel, which may not have been damaged.

It will only do either of these two things successfully if trees are allowed to fall in and create energy hot-spots, or fall in and sink to the bottom and set a new bed level with the silts and sands filling the spaces between, or so block the stream that the river is forced out of its banks and can find its way over-time to its original course, or maybe carve a new one. Or all the above.

Trees kind of matter therefore. They are critical to the process.

Amazingly, on the River Wensum in this reach, they had been falling in and falling and falling in and no-one had come along all tidy-minded to remove them. And bit by bit the stream was doing amazing things. I walked it in the high flows of the 2020/21 winter and took a load of photographs to record the process.

The top left image shows the river breaking out across the floodplain. The rest of the images are all taken in the woods to the north of the existing channel, and show the start of the process whereby a river starts to reclaim its former, natural pathways … so long as fallen trees are left in the existing channel.

The gallery below shows trees across the main channel which were facilitating this escape. The KEY difference between trees blocking a channel in this way and a flint weir of the type so often installed in well-intentioned “restoration” projects, is that the trees enhance the energy processes of the flowing stream, by creating pinch-points and blow-outs, whereas the gravel bar kills the energy processes by effectively impounding long tracts of the stream: the small energy release that occurs over the installed riffle looks good in photos, but is like lead face-paint to the ecology of the stream.

With all this process-driven self-restoration occurring on an SAC chalk stream, I had hoped the river was being left alone deliberately. I may have been wrong.

Last autumn I noticed works were in progress but was barred from taking a look by Heras fencing and Keep-Off signs. The little I could see through the barriers did not look encouraging. It seemed that the work was driven by the need to repair the footpath, but I could see that a lot of trees were being taken down and stashed untidily on the floodplain beside the raised path.

I went back this morning. The footpath is still “out of bounds” but given that a much more significant crime than trespass was clearly occurring along the river bank – and that lots of other people were also ignoring the injunctions – I walked down to take a look. I could see that some effort had been made to pin a few branches here and there into the edge of the stream. But set beside what had been taken out and – more than that – what could have been done with all the trees now felled and bulldozed out of the way, these efforts were pretty unimpressive. Large tracts of the stream are now wide open and tidy again.

This was mostly ecological vandalism with only a nod in the direction of river restoration or habitat mitigation. The process of self repair has been set back 20 years, sadly. I was a bit heart-bropken, to be honest.

What a missed opportunity! And more than that … what was the point? Did the footpath have to be repaired with enormous machines cutting a swathe through the place and tidying it up like Mrs Mop Transformer?

You say all this stuff about river restoration and everyone nods and sometimes you wonder if anyone really gets it. It’s about PROCESS. So, don’t do stuff that kills process. Least of all on an SAC! FFS.

Whose the beneficiary here … bats and fish, or people?

Sort of trying, in that one limb has been left over the stream … but why remove the lower limb, the one doing all the work?

What purpose was served by the removal of that?

Or that?

Nice and tidy, at least, with none of that messy stuff in the way.

Meanwhile, that flint weir continues its work robbing gradient from hundreds of yards, to spend it all on ten.

So … here’s an idea. Why not do what the Wensum wants to do if only we would let it. Let’s put it back into the blue channel, and for public access create a suspended board-walk that intersects the stream, but doesn’t snuff the life out of it.

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