LIFE ON THE CANALS

Canal banks : a return to "green" solutions !


Yachts and cruisers leave the lowest chamber of the triple lock at Trollhättan. The fourth lock is in the background, behind the basin excavated in the rock.


The four experimental sites for consolidation of banks of the Canal des Deux Mers in Midi-Pyrenees region have all been developed and planted, and a works reception visit took place in late June.

A delegation of 15 elected representatives and technicians from Midi-Pyrenees Regional Council visited the four VEV experimental sites: Deyme and Castanet on the Canal du Midi, Lacourtensourt and Montech on the Canal latéral à la Garonne, to assess and discuss the different aspects of the works just completed.
The picture taken during the visit shows part of the bank treat-ed at the Deyme site, 4km upstream of Vic lock on the Canal du Midi.


   D.R
   Site de Deyme, en cours de travaux


Behind the plane trees is the cycle path laid out by the département of Haute-Garonne. The site presents an open landscape, in a rural environment, but on the immediate outskirts of the Toulouse metropolitan area. It was thought preferable here to preserve visibility, avoiding the more imposing shrub beds that were considered appropriate on other sites.
At the bottom of the slope, the former towpath had almost disappeared over a few kilometres as a result of bank erosion. The first task was to restore the original bank cross-section by making a berm, at the edge of which two rows of willow piles, up to 2m long, were driven in at 50cm intervals. These piles effectively pin onto a small platform small willow branches, over which are laid, linearly, fascines of conifers, completed by a compacted earthy material. This bank protection should effectively dissipate the wave energy caused by the boats' wash, thus protecting the young helophytes planted between the piles and the slope. The helophytes planted on the berm are scirpus, reeds, creeping-jenny, sedge and Deschampsia.
It should be noted that the narrowing of the canal surface by 1 to 2m does not affect the navigable conditions, since the final configuration corresponds to the former dimensions.
Evaluation of the four projects will provide valuable information and comparisons, especially as the four sites present widely varying conditions.
At Lacourtensourt, for example, the landscape contractors and VNF (project manager of behalf of Midi-Pyrenees) have already reported the theft of a significant number of newly-planted shrubs, as well as the malevolence of water rats which have literally devoured the alder saplings. This rodent, an unfortunate (and accidental) import from Northern America, had already been responsible for making the Montech Canal embankments permeable, forcing VNF to close the canal around 1990.
The life of a waterway engineer is thus full of surprises, often unpleasant, hence the importance of the programmes for restoration and raising awareness of riparians and users, to minimise the disorders and facilitate future maintenance.
Midi-Pyrenees Regional Council and VNF in any event hope that it will be possible to benefit from these experiments to develop a large-scale restoration programme, which would render the canal's original aspect and cross- section, thanks to the reintroduction of vegetal engineering techniques.