Hydro-sedimentary monitoring: an indicator of success

Hydro-sedimentary aspects are at the heart of the operation’s success. The studies that have been carried out since 1995 show that it is urgent that action is taken. The heavy build-up of sand around the Mont, due in particular to human operations over the centuries (land reclamation and channel of the Couesnon in the XIXth century, development of a car park on the strands from 1950 and construction of the first dam over the Couesnon between 1966 and 1969) threatened to connect the Mont to the continent by 2040.

The first studies carried out by the SOGREAH Laboratory (Grenoble) between 1997 and 2001 enabled the scale of the situation to be assessed and the solutions to be implemented to be analysed and approved.

As the project entered its operational phase in 2005 and the new dam over the Couesnon was brought into industrial service in May 2009, increased monitoring of the expected results and observed effects is necessary.

The new models and monitoring must enable the effects of the structures produced to be studied and analysed in order to ensure that the operation produces the desired results: that the Mont-Saint-Michel is once again surrounded by water and sand.

An international and independent scientific commission and the Syndicat Mixte are monitoring the hydro-sedimentary effects of the flush system and are checking the results obtained.

Environmental monitoring: high quality objective

The quality and diversity of the Mont-Saint-Michel bay’s natural assets are recognised at international, European and national level. A wetland of international importance (Ramsar Convention), UNESCO world heritage site, Natural 2000 site under the European "Habitat” and “Bird” directives, ZNIEFF cover all or part of the bay’s territory. These various statuses complement each other and many of them have regulatory implications intended to preserve the site’s extraordinary biodiversity.

The operation to restore the Mont-Saint-Michel’s maritime character has set itself a major high environmental and landscape quality objective, within this regulatory framework.

During the development phase, the 2002 impact study identified the project’s potential effects on the environment, defined the reduction, correction or compensatory measures to be implemented and identified the monitoring obligations.

At the end of the public enquiry, the inter-prefecture authorisations in 2003 specified the content of the monitoring programme. An Information and Monitoring Commission was also established, with the objective of providing information to administrations and local users.

In order to meet these regulatory requirements and the objectives of the impact study, the monitoring programme must assist the project over the long term and, if necessary, optimise the management of the work. Monitoring the effects of the work on the environment requires monitoring of the physical and chemical quality of the Couesnon’s waters and monitoring of the noise emissions around the sites.