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The first in a series of blogs for river restorationists. The reason why nothing has appeared on here for the past four months: I’ve been a bit busy helping the Norfolk Rivers Trust deliver a handful of river restoration projects on the River Nar. This one at a site near Castle Acre will start the series because today is the birthday, or rather the re-incarnation day of a lost river. The aerial photo (1946) below shows a part of the River Nar which was changed from its natural course hundreds of years ago when the mill-leat for the downstream mill was cut: the straight channel flowing down the west (left) side of the image. Look east a few yards however and you’ll see evidence in the ground of the abandoned river. In fact it was left there, unfilled and unchanged from the day it was cut off by the leat until today, the 11th of November 2014.

This relic channel is a true rarity on English chalk-streams. More or less every yard of every river has been modified for one reason or another. To find five hundred yards left more or less as the Ice-Age made them was the rivery equivalent of finding the tomb of Tutankhamun. The relic channel was cut off at its upper end and at the lower end was joined to the mill-leat by another straight, man-made channel. This project then was about re-instating the old channel by creating a short linking channel upstream and a longer more natural one re-connecting back to the meandering part of the main river downstream.

The lower channel accounted for 80% of the project time. The available route passed through a slightly raised part of the flood-plain and in the middle reaches it was a challenge to peel away enough ground to make the correct, naturally shallow cross-section. There was little fall to play with too and the main river to which the new channel returned has been dredged (a future project will be sorting that out) and so tuning the gradient proved very tricky. It was worth the effort though. When the flows finally broke through the new channel worked perfectly, with good velocity and no unintentional impoundments.

Restoring the relic channel was as close to actual river restoration as is possible: like peeling varnish off an old painting. A delicate job if the painting is not to be damaged. In practice we went so lightly that it was quite easy. Helen Mandley supervised with an eagle eye and Wayne on the digger performed with great sensitivity. See the photos below for the fuller picture. Amazingly there was very little sediment in the relic channel. Within an hour the flows had scoured their way to the gravel.

Some will know that Nigel Holmes sadly passed away a few weeks ago: it may well have been Nigel who first identified this as potential restoration project in a report (which he co-authored) commissioned by English Nature about ten years ago. This project has been a team effort over the years and Nigel’s early involvement is a reminder of that. I’m sure he would have been chuffed to see it come to fruition. The delivery team included WWF and Coca Cola as sponsors, the Norfolk Rivers Trust as planners and supervisors (Helen Mandley ran the project, and I was there to help fret about gradients, planforms and cross-sections), the Norfolk Rivers Drainage Board (machinery and delivery – thanks to Adrian, Wayne and Graham), Richard Hey, Holkham Estate, The Castle Acre Fishing Club, Natural England and others.

Emmanuel's3 — The red lines mark the new connecting channels. The blue lines mark the “lost” relic channel.

DSCF5491 — The old mill leat. The channel is too wide and straight and has been dredged in places too: which is why it is over-run with burr-reed, while the river tries to establish a more appropriately-sized channel along one edge.

DSCF5496 — This is the ground which the new connecting channel was cut through at the lower end of the project: an old poplar plantation and defunct pheasant pen.

DSCF5533 — The relic channel under the trees. The water in this image is just flood-plain seepage, which amounted to just enough flow to keep the channel viable for the past two centuries. Note the shallow profile of the un-modified banks. The channel is shallow too, only 30 cm deep, with a bed of hard gravel under a thin layer of sediment.

DSCF5636 — The relic channel in the open meadow. Here the old river is almost lost under vegetation, although in practice it was quite easy to uncover it. Note the shallow banks and the fabulous tussocks which the river meanders between. The bed is hard gravel in a shallow channel under a thin layer of sediment.

DSCF5645 — The relic channel revealed. Without touching the bed or banks the weed was peeled aside and folded over onto the edges of the stream.

DSCF5649 — Helen Mandley of the Norfolk Rivers Trust making sure the digger doesn’t damage the bed of the relic channel. The operation was a wetter version of peeling varnish of an old painting: just enough to reveal what’s underneath.

DSCF5666 — The new channel flowing where the pheasant pen used to be. Still something of a moonscape it will be softened in due course by large woody debris and plants in and along the edges of the channel. The important thing was to replicate the dimensions and planform of the relic channel upstream. Establishing half-a-dozen subtle riffles when there was very little fall to play with was quite a challenge, as was creating shallow banks when the floodplain on the available route was slightly higher than ideal.

DSCF5667 — Another view of the new channel.

DSCF5670 — A wonderful moment: the relic channel flowing as the main River Nar for the first time in about two hundred years. It looks happy!

DSCF5675 — The same wonderful moment upstream: the river looks almost pre-historic. This is a very special site now: a reference reach of an unmodified English chalk-stream. Hen’s teeth are more common.

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.