Sienne Havre

© Larrey&Roger / Conservatoire du littoral
© Larrey&Roger / Conservatoire du littoral
© Larrey&Roger / Conservatoire du littoral
© Larrey&Roger / Conservatoire du littoral
© Conservatoire du littoral - Attractiv
© Conservatoire du littoral - Projet LiCCo
© Conservatoire du littoral - Projet LiCCo
© CERReV. A Diaw
  • Previous
  • Next

The Sienne Havre is emblematic of the issues within the havres on the Cotentin west coast . The notion of integrated coastal zone management has much significance here.



In the Manche department, the havres coast on the west coast of Cotentin is subject to two phenomena: sedimentation of the havres and erosion of the coastal zone. The economic activities (shellfish farming, agriculture, tourism) on the Sienne Havre are dependent on the evolution of the coastal zone and sea level rise.

The project will use information from the SURCOTE project (LITEAU programme) to share existing expertise. There are ongoing deliberations on land use in this area, which covers the maritime domain, such as moorings, shellfish farming, saltmarsh… which emphasise the need for a more integrated approach of management betweenland and water in light of the major changes expected in this area, both in terms of the impacts on biodiversity and coastal erosion.


Summary of the issues

The Sienne Havre is facing coastal erosion as well as tidal and fluvial flooding. In light of this, two major issues have been identified for the management of the natural environment:

  • in the sector of Montmartin-sur-mer, the saltmarshes are almost as much under attack as the dune cordon by the arm of the Sienne which extends east. The environment would be changed if the dunes were to disappear following recurrent phenomena of erosion, sea submersion and flooding.
  • Birdlife – the Sienne Havre is of international importance for the wintering of the Pale Bellied Brent Goose. 90% of the national population of Pale Bellied Brent Geese overwinter to the south of the Agon Point, on the dynamic part of this site. A change in the natural environment could have a significant impact on this species.


The impacts on usage might affect:

  • shellfish farming activities following changes in the nutrient content caused by the evolution of hydro-sedimentary processes in the Havre.
  • agriculture: a change in the land environment following sea submersion would have an impact on the salt- marshes, leading to their disappearance. This environment represents grazing land.
  • tourism: a gradual sedimentation of the havre would have an impact on boating activities in terms of access and mooring possibilities. The “Exemplary Yachting Port” project by the Communauté de communes de Saint-Malo de la Lande won awards in 2009. The project aims to find solutions to compensate for the decrease in the number of days when boating activities are possible in the Havre due to its sedimentation. Thus the music festival “Chauffer dans la noirceur” is held in July every year in Montmartin-sur-Mer. The event takes place in a seafront area particularly vulnerable to any change in the coastline.
  • Infrastructure such as the road systems, the Regnéville seafront and the camping grounds in Hauteville and Regnéville, which are located in the risk zone.

Ongoing work and how it links with LiCCo

As part of LiCCo, on all French pilot sites there will be:

  • a study on the functionality of the environments;
  • a study of the evolution of the shoreline over time and land use;
  • a socio-economic study;
  • a comparison of methods and results between sites at regional and cross-border level;
  • an assessment of the reliability of the data gathered in the long term.

The main objective of LiCCo on this site is to raise awareness amongst local stakeholders so that they anticipate coastal change in their management approach. On this site, the LiCCo project will link with the Surcote project piloted by the team from the University of Caen, as part of the LITEAU programme. A link is also envisaged with the planned marine park in the Norman-Breton Gulf.  LiCCo will have the support of the Conservatoire du Littoral management committee to organise the site workshop.
The data produced within the scope of the LiCCo should also give a clearer picture of the “Exemplary Yachting Port” project. The continued existence of the port within the Havre is heavily dependent on the evolution of the coastal zone and the morpho-sedimentary changes in the Sienne.


LiCCo partners for the Sienne Havre

  • Le Groupe d’Etude des Milieux Estuariens et Littoraux
  • Le Centre d’Etudes et de Recherche sur les Risques et les Vulnérabilités


Key stakeholders

  • Le Syndicat Mixte des Espaces Littoraux de la Manche (SyMEL),
  • Le Comité Régional de la Conchyliculture (CRC),
  • Les Communautés de communes du canton de Montmartin-sur-Mer et de Saint-Malo-de-la-Lande,
  • The neighbouring communities (Agon-Coutainville, Régneville, Montmartin-sur-Mer, Tourville-sur-Sienne, Heugeville-sur-Sienne, Hauteville-sur-Mer),
  • L’Agence des Aires Marines Protégées (AAMP) via the marine park planning mission
  • La Direction Départementale des Territoires et de la Mer du département de La Manche (DDTM 50).