Thursday, 4 December 2014

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.


Susan said...

Maybe you'll have to hope that chikungunya makes it here sooner rather than later -- that'll discourage anything that might lead to more mosquitoes.

Pollygarter said...

I don't know which is worse, personally!