Weir, art thou going? River improvements part III

Our posts here and here about the programme of improvements to the Claise basin described the achievements in our corner of the Aigronne valley, out of 77km of river bank works in the last three years.

Now operations have started on the section of the Claise between Le Grand Pressigny and Etableau. If you go down the rue des Réaux towards Abilly you will see, or rather you won't see, the familiar line of poplars screening the decaying former furniture factory building near the déchetterie.

Stumps, logs and branches next to the Iron Bridge

The trees that remain, apart from the big oak, are mostly small alders.

View towards the weir from the Iron Bridge. The house behind the high hedge to the right is for sale.

.

See "Improving the Aigronne Part II" for a translation of the poster

Poplar is an excellent timber, widely used for construction throughout France, and good poplar wood is valuable. The tradition was, when a daughter was born, to plant a poplar plantation to pay for her dowry when she got married. But these trees were too far gone. The smaller notice describes how the trees will be disposed of. Given that a Prefectorial edict obliges the commune to do the work; that turning dead and fallen trees and branches into biomass is not easy to do cost-effectively; and that the cost of hiring the mulching equipment needed to compost the remains is beyond the resources of the town council, SARL ETREN is authorised to burn what it cannot turn into biomass.

The field behind the digger is scheduled as building plots

The poplars were rotting at the heart, potentially dangerous, and they had to go. The weir is in the background.

You can read the small poster if you can fly. But it's important!

Be that as it may, the poplars were in the way of the really big undertaking.   Under the European directive on water courses and La loi sur l’eau et les milieux aquatiques (LEMA), the commune has to remove (literally, to "suppress") the weir, and return the river to a semblance of its original state. Given that water mills have been in existence since classical times, we are talking prehistory here.

La Nouvelle République in its article of 22nd November 2014 describes the weir project thus:

in May 2015, the barrage will be removed and the bed of the Claise re-aligned, rebuilding part of the banks with rock, earth and pebbles, with the objective of reducing the width, giving back to the river an appearance of the original bed, permitting the water level to rise and restoring the rate of flow.

The weir from the town bridge

The weir was built in the 1970s to provide a swimming area and sustain the water level in periods of low water. It is now obsolete. Nobody wants to swim there: the water is dark and forbidding, the bottom is squidgy and covered with leathery, slippery poplar leaves, and there's a heated public swimming pool on the other side of town. La NR continues:

the prefectorial mandate governing the operation of the weir obliges the commune to keep it open for nine months of the year. This obligation has never been respected. The repeal of this mandate will require the community of communes of Touraine du Sud (CCTS) to remove the weir and return the site to a fit state. The CCTS's land management brief makes the work possible. A partnership with the region [Centre], the département [Indre et Loire] and the water agency [for the Loire and Brittany] allows the rehabilitation of the site to be incorporated in the restoration program. This new project will be 100% subsidised.

 See also the CCTS web site here and here.

Suppress the barrage? Sounds simple enough. No big deal. A bigger deal will be the heavy lorries thundering past carrying the "rock, earth and pebbles" to the site and thundering even louder as they return empty at top speed. A major issue will be disposing of the tonnes of concrete of the barrage itself and the spillway, and the unknown tonnage of silt (la vase) deposited behind the weir. Where will it go? How much is there? How many lorryloads?

And just what is meant by the river's original bed? When the ground is saturated, it is easy to trace old meanders of the Aigronne, for example in the fields south of Rivau. The Claise valley between le GP and Descartes opens out to become several kilometres wide, the site of a prehistoric swamp/lake bed. Watermills go back to the times of Alexander the Great; human life in the Aigronne and Claise valleys goes back to the Upper Palaeolithic, 350,000 years ago. How far back should we go in restoring the river to its "original state"?

For us, the biggest issue of all will be when the sights are turned on Richard's weir and sluice gate that direct  the Aigronne's flow into the bief that runs past our house and the Moulin de Favier. That weir has been there for at least two hundred years, and is shown on the Napoleonic cadastral map of 1812. The mills existed when the Cassini  maps were drawn in the 17th century, and, since La Forge was an undershot mill, there must have been a weir too. The Cassini map does not show such fine detail. The sluice is new (1980s) and was constructed along with the étang. It is left permanently open.

The Dechartes have a history of the Moulin de Favier going back to the 12th Century. The habitat supports at least one nationally proteced species - the water vole - and local rarities like the Large Pincertail dragonfly. We have a duty to preserve la patrimoine, be it history or nature. On the other hand, everyone has a right to clean water, including the migratory fish such as eels which are blocked by such barrages.. I'm not quite sure how turning our bief into a stagnant ditch full of mosquitos will improve the milieu aquatique.

And the history of Le Moulin de la Forge is a matter for another post.

Improving the Aigronne part II

The planned amenagement of the Aigronne valley continued rapidly this spring between Le Grand Pressigny and at least Charnizay. The work we blogged about here to improve the river flow has settled in nicely, with green algae and sediment softening the whiteness of the new stone. The "restoration" of the riverside vegetation has proved rather more controversial.

Acting to preserve the environment

Vegetation in a bad state:

     presence of unstable trees, leaning, withering, dead
     poplars in great numbers
     zones inaccessible to users (fishermen... )
     presence of trunks and branches in the bed of the river

Work done:

     Cutting down trees threatening to fall into the river in the medium term
     Creation of clearings to enable users to reach the river
     Selective removal of encumbrances on the river bed

Many of the poplar plantations in this area are way beyond any economic return, being good for nothing but firewood. Poplar is an excellent constructional timber, and according to one tradition we have heard, new parents plant poplars on the birth of a daughter, with the eventual proceeds to pay for her dowry. That would make a poplar harvest at about twenty years old, but many of these trees are much older. They are loaded with heavy balls of mistletoe (gui), and many trunks have heart rot.

Rotten poplar trunks near Le Moulin Neuf

The stump in the foreground of the picture above typifies the problem trees. It is all that remains of a poplar that crashed across the road in last winter's storms, which tipped it over roots and all. The stump has been carefully relocated, to preserve the line of the riverbank and the streamlet that empties into the river via the ditch.

It is good to see so many of these rotten old poplars waiting to be taken away. We are speculating whether some of the large piles of "lop and top" such as the one on the far bank are awaiting a mobile chipper so the scrap wood can be made into pellets for fuel.

 
But the scale of clearing along the riverbanks is causing some riverains some concern. Along the Aigronne. and its tributaries such as the Rémillon below La Celle Guenand, all the riverside trees and shrubs, regardless of species, have been coppiced (cut to the ground) in some places. Yohann Sionneau, the river technician, insists that his team have been removing nothing but poplars, in accordance with their policy. But, he said, some individual proprietors, working on their own stretches of river, had been rather too enthusiastic.

Bare banks - not much cover here!

Coppicing will not kill the living trees, and is necessary from time to time, but for so many proprietors to do it simultaneously is "too much" as our neighbour Anne said. The trees will regrow enough to provide some cover in a couple of years. However, before that happens the amount of shade along the Aigronne - a premier trout stream - between Charnizay and Le Grand Pressigny has been massively reduced, all at once. In hot weather the water will become warm, the oxygen level will fall and the fish will die. We have heard from someone involved with La Gaule Pressignoise (our local fishing association) that of a recent release of trout, six were picked up dead.

The trees and shrubs along the river provide an essential wildlife corridor, linking isolated patches of woodland and enabling birds, mammals and insects to find food or a mate or a nest site or somewhere to roost. The cover will grow back, but right now the banks are bald. We have not seen a single squirrel this winter - we saw them regularly last year. However we have heard three great spotted woodpeckers drumming simultaneously at different points along our still-covered stretch of riverbank. We have not yet heard an oriole, that lover of poplar plantations - many poplars have gone, but there are still plenty left for the orioles.

Wildlife corridor along the Rémillon

Improving the Aigronne

Just recently, a big poster appeared by the Aigronne bridge, advertising aménagements du lit (improvements to the riverbed).

Aménagements du lit

Then a succession of dumper trucks began clattering to and fro past the house, delivering their contributions to a series of piles of white stone, mainly small but including some very big ones. At peak there were four different trucks passing at approximately quarter-hourly intervals. Then a big digger arrived and started nibbling away at the stones, depositing it carefully on the river bed between Gatault downstream of us and Le Moulin de Chevarnay upstream.
We had learned of the plan to improve the flow of the rivers and streams that make up the Claise basin at the Fête de la Chasse at Preuilly sur Creuse, but we hadn't appreciated that it was going to happen so soon. As Yohann Sionneau, the river technician, explained to us, many of the river banks in our area are effectively canalised in places, the numerous poplar trees at even spacings with every trace of cover for small wildlife scrupulously removed. The flow is too smooth and uniform between these pared-down banks, reducing thediversity of habitat. In places the bed has become too wide, so during periods of reduced flow, particularly in summer, the water becomes very shallow, reducing the oxygen levels. There is also too much silt, denying the fish access to the gravel beds where they spawn. All these factors diminish the biodiversity of the Aigronne. The project was financed by the water authority for the Loire and Brittany; the prefecture of Region Centre; and the community of communes of Touraine du Sud.

Using the stones, shingle banks and rocky outcrops have been created, so that the flow rate and depth of water are more varied. Increased turbulence allows the water to pick up more oxygen. When water levels are lower, the shingle banks reduce the width of the channel, so that such water that does flow is deeper. Thus the river bed is improved for wildlife, especially aquatic species such as - er - trout. Oh what a giveaway.

Destined for the riverbed

The work was done by a large digger and, whilst the large stones were dumped on the side, the main loads of smaller calcaire were dumped directly into the river. The digger then collected a bucket load and took it to where it was to be used.

This did make the river very cloudy to begin with as the powdered calcaire was washed out... but the river is now nice and clean again. We'll put up more shots of these bits over the seasons.