Marsh poitevin

The unit that constitute the marsh poitevin and the Baie of the Pivot (relic of an old marine gulf) extend on approximately 100.000 hectares, with horse on three departments (the Vendée, Two-Sevres and Charente-Maritime) and two areas (Pays of the Loire and Poitou-Charentes).

The space given up by the ocean with the wire of time little by little filled alluvia of marine origin (the BIS) or river. The result is a great plane extent, of which the altitude located at an intermediate level between that of the high tides and the low tides. The desiccated marshes cover a surface of approximately 47.000 hectares. The wet marshes (of which the Eastern part is described as Venice Verte ) cover for their part a surface of approximately 29.000 hectares, while qualified marshes of intermediaries (what means that they are imperfectly desiccated) represent approximately 19.000 hectares.

History

At the beginning, the marsh poitevin was a zone covered by the sea (the Golfe of the Pictons). Gradually, the latter was withdrawn, leaving behind it a marshy zone which continued to be filled, naturally and from the action of the men. Traces of occupation pre and protohistoric were identified on its old banks like on old the island S now included in the grounds.

As from the 7th century, large feudal lords proceeded to donations of parts of the marsh for the benefit of the Abbaye S neighborhood (most known are Maillezais, Nieul-on-the Autise, Absie, Saint-Maixent, Saint-Michel-in-the Herm); alteration work was thus launched, with an aim of exploiting in more organized way the productivity of these mediums (cultures, breeding, Saliculture, Pêcherie S…). The first Endiguement S of desiccated marshes were carried out at that time, just as were dug there the first large evacuation channels, like the Canal of the Five-Abbots, with the evocative name of this context.

The area having been the framework many confrontations during the Wars of religion, much of destruction were operated at the time, doubled of a lack of maintenance of the works of drying.

Work of drying is resumed and intensified under Henri IV, which, from the point of view of rebuilding, grants various Privilège S to investors Huguenot S originating in the Netherlands. Appointed Large Master of the dams of the kingdom by the king, the Flemish engineer Humphrey Bradley does not intervene however in the Marsh poitevin. The duke of Roannez, governor of Poitou as from 1651, seeks financings to undertake work in the long term. Large aristocrats of the Court are not long in foreseeing the profits which can be drawn from these dryings, in spite of the many difficulties which they encounter in their realization.

Napoleon 1st takes in 1808 a decree of installation of the Niort Sèvre, to consolidate the navigable vocation of it. This decision constitutes the 1st act of a work campaign great which goes, between the beginning of the 19th century and the beginning of the 20th century, to give to the marsh wet the aspect that we know to him today. One can also consider this decree, which places the police force of the navigation and the water of the domanial river under the single responsibility of the chief engineer of the Highways Departments of Two-Sevres, gives a catchment framework of management in conformity with the hydrographic logic of the area of Sèvre Niort. Contrary, creation under the French revolution of the departments artificially divides this space between the the Vendée, the Charente-Maritime, and the Two-Sevres.

Under the Restoration, a royal decree of Louis Philippe (“To all, present and to come, hello! ”) structure marshes wet in departmental trade unions owners. These trade unions federate thereafter in a Union of the wet marshes, whose vocation is to ensure an overall coherence on this territory. It is during this time (as from the years 1835 and until about 1850) that are bored or arranged the spillway canals and large “drains” such as that of Garette. Great hydro-agricultural work was completed in the years 1960 (Remembrement S, creation of new crest gates, re-callipering of channels), then in the years 1980 (development of the agricultural Drainage by Drain S buried), from the point of view of generalized draining and intensification of the agricultural production, with an increasingly marked specialization of the exploitations in the cereal cultures.

Blow, a polemic was born from the overexploitation of the hydraulic richnesses of the sector. The forced draining of the marsh poitevin caused a retreat of the Biodiversité, in particular for a very great quantity of birds (more than 250 indexed species). The downgrading of the Regional natural park in 1997 caused a handing-over in question in all the actors of the place who must work jointly not to destroy a very particular and fragile natural space.

Typology of the marshes

The channels have various names, according to their importance (increasing): the ditch, the conche, the Level, the water road, the broue, the gonnelle one, the drain, the channel, theclub-footed one (…). The drain is a way larger than the conche it even larger than the ditch.

The term “ marsh desiccated ” does not mean that there is no more Eau but which it is not easily flooded any more, contrary to the “ marsh wet ” which is it.

There cannot be marsh desiccated without wet marsh. Indeed, this last acts as a sponge which makes it possible to control the contribution of water coming from the Bassin pouring. Water of Inondation S is épandent there, which protects the marsh desiccated from the Crue S. Autrefois composed of vast spaces of meadows, the desiccated marsh was gained during the 20th century by the intensive cultures (Céréale S, Maïs, Tournesol…).

The desiccated marsh is in fact a Polder. It is encircled of Digue S which protects it at the same time from the sea and the water of the Bassin pouring. Water is evacuated by means of doors with flood (or doors with the Mer) which let leave water to low Marée. With high Tide, the pressure of the sea closes the doors and prevents the salt water from ebbing in the cultures. During the dry season, the doors with flood are closed, in order to keep water necessary to the natural Irrigation by the ground.

The marsh wet being tributary of the Inondation S, it is what explains why cultures of short cycle developed there, as that of the mojhettes (Haricot S white) whose cycle is three months, which corresponds to the period except risk of flood. The breeding was a long time the principal activity of the wet marshes, where developed dairy Coopérative S. The agricultural déprise currently results in an insufficient maintenance of the channels which border the grounds. In certain places, the owners tend to join together their contiguous pieces to form only one of them. The combined consequence of such a regrouping and a lack of maintenance leads to a less effectiveness of the wet marsh which ensures less and less well its roles of sponge, regulator and filter purifying water.

Since the years 1980, the context of intensification of the productions was translated as a whole marsh by attempts at introduction of the Maïs, but the constraints related to the mode of water (floods of spring and/or autumn) made that this culture did not produce the anticipated results there. It developed on the other hand much on the slopes limestones bordering the marsh, with in corollary the installation of practices of Irrigation. It can even arrive, at certain times and in certain places of the marsh, to see water going up upstream, because it is the river which is thrown in the ground water…

Since the origin, a conflict exists between the farmers of the wet and desiccated marsh. Those of the desiccated marsh inherited prerogatives on the management of the valves. In period of Dryness, they irrigate their grounds with the water stored by the wet marshes, putting in danger the cultures and the breeding in these marshes. This phenomenon, although old, is still accentuated nowadays by the intensive culture of the corn, which is a culture of summer in the area. The culture of corn in the middle same of the marsh encouraged the managers as much as possible to evacuate water during the wet season to avoid the floods which would have compromised the sowing, thus depriving the marsh of its role of sponge (it stores water to restore it at the season dries). Another phenomenon rises directly from the combined effects of the drynesses and management of water: the lack of water strongly reduces the flows of the rivers of the Poitevin Marsh (Separates it Niort and the Lay), which has as a consequence the dramatic acceleration of a natural phenomenon, the silting. The silting also increased in consequence of the abandonment of the clearing out. That strongly compromises a whole side of the littoral economy of the Marsh Poitevin, the Conchyliculture, and many conflicts of interests are born between the farmers and the oyster culturists and mytiliculteurs from Bay from the Pivot. The revival of programmes of maintenance of the marsh is in hand.

The Poitevin Marsh is a medium fragile, artificial, mainly drawn by the man, but subjected to the law of hydraulics. Fed out of fresh water by the rivers and coastal brooks of the basins slopes of Separates Niort, of the Vendée and of Lay, this medium is perpetually in unstable balance. The marsh is not a linear space, it is not even a juxtaposition of river, it is an organization complex, three-dimensional, whose channels are like the blood-vessels of the human body. Modify the blood pressure, it is your organization which crumbles, remove the dams of protection to the sea, you will obtain an effect of marling which will flood very with high tide and will drain the channels with low tide.

The maintenance of the medium is the result of a subtle balance of management of fresh water: it is necessary to evacuate the too full one in times with raw (what is not possible that with low tide) and to keep water in period of low water level. According to the years, in the event of severe low water level, it can happen that the works which manage the estuary remain closed several months of at a stretch. It was the case in particular in 1989.

Life of the marsh

The draining of the marsh being artificial, its maintenance in state requires a permanent maintenance: The ditches must be cleaned for not envaser, the banks must be consolidated not to crumble. One thus finds various trees planted especially to this end:

- The Peuplier S are very present in the wet marshes, from which they structure the landscapes. The white of Poitou (local name or endemic species?), giving a very required Wood, is less and less exploited today, other species becoming ripe more quickly.

- The Ash and the Weeping willow. They are cut out of tadpoles, i.e. one does not let the trunk push with the top of one meter fifty or two meters. The tree is thus squat, and develops an important network of roots which maintains the banks. Size of the " têtards" allows to know the original use of each piece: a piece bordered of trees cut with less than one meter fifty was probably dedicated to the truck farming, while higher trees indicate a meadow of breeding.

The marsh sheltered formerly many Anguille S, being the subject of a traditional fishing by means of specific machines: bow nets, bourgnes, etc the species today is very threatened because of surpêche of the elvers (or elvers, names given to eel alevins) in the estuaries, on their arrival of their birthplace (probably the Sargasso Sea). Indeed these small fish are very required and the selling rates reach enormous sums, which encourages the poaching.

The Coypu S, a species introduced, without predator and very prolific, are an main issue because of the devastations which they cause with the banks. These animals can be vectors of the Leptospirose, factor of abortion at the bovines. They were the subject of catastrophic poisoning campaigns for all the food chain. This practice from now on is prohibited and recently replaced by the trapping, method more selective.

One finds also Loutre S of the Héron S, Pluvier S or others wader S. Other exotic species being invading pose problems: the Jussie (Ludwigia sp.), the Myriophylle of Brazil (Myriophyllum aquaticum), the American crayfish (Orconectes limosus) and the crayfish of Louisiana (Procambarus clarkii)

A regional natural park

There was a Regional natural park (Regional natural park of the Marsh poitevin, Valley of Sèvre and the Vendée) of 1979 with 1996, which covered the marsh and of the neighbouring natural zones.

Certification was not renewed in 1997 following a very unfavourable assessment of the evolution of the marsh due to intensive husbandries with regard to the extensive breeding formerly present. The communities members of the mixed trade-union which managed this park did not know to get along on a new charter which is compatible with the statute of Regional natural park and which would have shown a will to rectify the bar.

In 2002, the steps aiming at new obtaining the label were started.

While waiting, it is necessary to be satisfied with a “Interregional Park of the Poitevin Marsh”, acting all the same a minimum in order to protect the ecosystem. This mixed trade-union whose President-in-Office (2006) is the green personality , Yann Hélary, is in charge of the drafting of the new Charter for a Regional natural park.

External bonds

Site of the interregional park
Site of Coordination for Defense of the Marsh Poitevin
Site of the House of Small Poitou (écomusée of the desiccated marsh)
panoramic Photographs of the marsh poitevin
Site of association Evail (history, operation and safeguard of the Poitevin Marsh)
Forum of the Atlantic Marshes Pole relay in favor of the littoral wetlands Atlantic Sleeve and the North Sea

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