Les digues de polders littoraux comprennent plusieurs catégories : digues de mer, digues de rebras, digues dormantes et digues ruinées. Dans le marais Poitevin, la tempête Xynthia, pendant laquelle la mer a atteint un niveau exceptionnel, a submergé l'ensemble du réseau des digues. Elle a permis de prendre conscience de l'état du réseau des digues et de l'absence d'une ligne continue de digues dormantes d'un niveau suffisant pour limiter l'extension de l'inondation.Des solutions adoptées ailleurs en Europe, comme la transformation des polders en polders d'été ou la dépoldérisation n'ont pas été envisagées. La réparation à l'identique, avec un renforcement a été adoptée. D'une façon plus générale, des indices sont proposés pour aider à la gestion des polders littoraux. Ces indices doivent tenir compte de la valeur écosystémique des schorres dont la biodiversité et la productivité sont exceptionnelles. La nécessité de quantifier les enjeux – ce qui est certes difficile – apparaît d'autant plus nécessaire que la montée du niveau de la mer risque de contraindre une politique de maintien rigide du trait de côte à des investissements disproportionnés à long terme.
Polder dikes coasts include several categories: sea dikes, sleeper dikes and devastated levees. In Marais Poitevin, during the storm Xynthia, the entire network of dikes has been flooded due to the exceptional level of the sea at that time. This situation has raised awareness of the status network of the current network of levees and of the lack of a continuous line of sleeper levees at a sufficient level to limit the extent of the flooding.Solutions adopted elsewhere in Europe, such as processing of the polders in summer polders or depolderization have not been considered. The decision has been taken to repair at the same and to reinforce the previous defences. In a more general way, the elaboration of indexes has been done to improve the management of coastal polders. These indexes should reflect the ecosystem value of salt marshes whose biodiversity and productivity are outstanding. Although it may be difficult, the necessity to assess the different issues is necessary indeed because the rising of the sea level may force to maintain rigid coastline at a disproportionate investment in the long term
Deltas are measured by length, width, surface and protruding area. The fundamental geomorphometrical property of a delta can be expressed by the protuberance index proposed here as the ratio of the two latter parameters. In the delta seen as river ending, the radial distribution of the hydrographie network will be simple, cross-connected or tree-structured depending on different river discharge partitionnings. In the delta seen as a coastline, the layout is concentric with a succession disposal of sandy bars and shallow depressions usually briny or saline. The relative influences of tide, waves and river discharge are used to define a classification of embouchures based on W.G. Galloway's and extended to many cases. Delta resource management can be broken down into the river streams and the deltas themselves. In the latter areas, resources can be developed without altering the geomorphometrical and hydrological environment (fishing, hunting, extensive cattle farming...), with some environmental changes (rice fields, irrigated agriculture, salt flats...) or completely obliterating the natural features (industrial land reclamation, deep-water harbours...).
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