Evolution de la gestion des dunes domaniales : les nouvelles stratégies. Management evolution of the state-property dunes in France

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1 Evolution de la gestion des dunes domaniales : les nouvelles stratégies Management evolution of the state-property dunes in France Loïc Gouguet ONF 1 Amélie Roche CEREMA 2 Merlimont june 2014

2 From the south of Brittany to the Pyrenean Range, 378 km of state property dunes have been managed since the 19th century by the "Eaux et Forêts", a French national office which was created in the 13th century and replaced by ONF in

3 The dune mobility was seen as the greatest danger and foresters had to trap the sand and cover the dunes with vegetation. The management was directed to sand fixation, and afforestation. 3

4 The forest so created was the ultimate stage, and managed with traditional practices, to produce the main natural resources, resin and wood, to 1970s. 4

5 In the early 1980s, under the influence of scientists and emergence of new concepts of biodiversity in the public policy, foresters have reconsidered their management practices and adopted a "flexible control of the coastal dune. 5

6 6 This kind of management, based on multifunctionality, allows: Prevention of sand invasion of the hinterland; Protection of some rare and original ecosystems, species, landscapes and places of interest ; Contribution to a sustainable and reasoned tourism; Control of marine erosion (the sand stored in the foredune nourishes the beach during storm events).

7 7 Xynthia (February 28th, 2010) In France, the storm was revealing roles played by dunes in the hazards of marine erosion and flood.

8 With its experiment of dune management, ONF helped the French state to identify the dune ridges acting as tools of protection, first against flood, with the partnership of CEREMA. 8

9 9

10 This method was improved during the last winter. A succession of more than 50 episodes of storms showed the importance to study the erosion and the obligation not to separate erosion and flood, which depend nevertheless on two different public policies. 10

11 11 Dunes keep a large part of the coastal sediment supply and play several direct and indirect roles to prevent coastline retreat and marine submersion: Dissipation of hydrodynamic energy in coastal areas; Contribution to the sediment equilibrium of the dune-beach system by natural sand replenishment of the beach during storm events; Natural protection of low-lying coastal areas against sea flooding

12 12 Once dunes identified, what solutions? During the last winter, we saw solutions on different ways, according to local authorities:

13 13 But these solutions have disadvantage: High cost for the community Reduction in the beach Disturbances on the neighbour dunes Distort impression of safety for the populations It is nevertheless the most used solutions in France. Beach nourishment is not a current practice in France.

14 Technics usualy used for urban beaches are now in application to non builded dunes protecting urbanized lowlands Some towns raised sand of the beach towards the dune. To do this, they must: take the sand in a low level of the beach Take care of the salt and the shells in the sand, unfavorable to the vegetation Respect the coastline Protect the natural vegetation 14

15 15 In the 358 km of dunes managed by ONF, 113 km are in front of low zones (ground zones situated under the marine level of centennial reference). 19 % of them are identified as weak regarding flood protection

16 16 Since 2010, there have been several developments in law, and in the mindsets of population to take into account coastal hazards. It s continued work to explain dune functioning, and its basics needs Naturally mobile sand dunes provide a more dynamic coastal defence system which can adapt to storms and sea level change Local authorities are responsible for managing coastal land, and managers must recognise all the roles of dunes, in all their functions including protecting from coastal hazards

17 17 Thank You 1 - Office national des forêts 2 - Centre d études et d expertise sur les risques, l environnement, la mobilité et l aménagement