In 1992, the Water Law of 1992 gave a definition of wetlands. These are the ” lands, exploited or not, usually inundated or engorged with fresh, salt or brackish water on a permanent or temporary basis; vegetation, when it exists, is dominated by hygrophilic plants (which like humidity) for at least part of the year. “. These areas play a major role in the water cycle. They store water in times of flooding and return it in times of drought. The presence of wetlands and their numbers make it possible to benefit from quality tap water. In total, these areas represent 8.5% of the fresh water on earth.
In total, wetlands represent 8% of fresh water
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© International Office for Water
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A natural way to limit flooding
If humans sometimes acquire equipment or structures to fight against flooding, we must never forget that nature remains an effective means of participating in it. In fact, like sponges, wet areas can accumulate rainwater and spring snowmelt, to gradually restore the stored volumes. This retention capacity is useful for regulating floods and mitigating their effects (less sudden or less high floods).
According to the CNE, for example, between Mâcon and Villefranche-sur-Saône, the Val de Saône plays the role of an expansion zone for the floods of the Saône upstream of Lyon. To replace this natural infrastructure with a flood control dam, several hundred million euros would have to be spent.
The “sponge” and “spreading” effects of wetlands
The mechanisms for regulating floods are different depending on whether you are in the mountains or in the plains: when wetlands are located sloping, they slow down runoff and facilitate the infiltration of water into the soil. This is the “sponge” effect, thanks to which water does not flow directly from the land into waterways, thus avoiding too sudden or catastrophic flooding downstream.
© Conservatory of natural spaces Rhône-Alpes
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In the plains alluvial, wetlands annexed to rivers and streams (wet meadows, alluvial forests, backwaters) store the flood flows on either side of the watercourse, allowing excess water to spread, this which reduces the height of flooding. This is the spreading effect. In addition, depending on the vegetation of the wetland, the speed of the flood will be modified: the more the number of obstacles opposing a resistance to the flow, the more the speed will be slowed down.
© Conservatory of natural spaces Rhône-Alpes
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Indispensable to fight against drought
In addition, wetlands play a vital role in combating the effects of periods of drought. They allow water to be stored naturally, and gradually restore it during these periods. This helps to limit the drying up of rivers. That’s not all: with their waterlogged soil, their vegetation remains green almost all year round. They thus provide particularly popular fodder in the dry season, when other pastures are generally dry. It is estimated that 50.66% of wetlands in France have agricultural use.
Wetlands have another significant advantage: they are a real reservoir of biodiversity. These areas are home to 40% of the planet’s species, on which they depend. And, more surprisingly, nearly 200 new species of fish are discovered each year in freshwater wetlands.
Sites undergoing restoration throughout the Auvergne Rhône-Alpes region
In Ain, perched at an altitude of 760 meters on the commune Plateau d’Hauteville, the Marshes of Vaux constitutes a unique natural site.
Restoration of the Marais de Vaux, the largest wetland in Bugey
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© Conservatory of natural spaces Rhône-Alpes.
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With its 132 hectares, it is the largest wetland in the Bugey mountain and the second largest in the department. It is made up of a diversity of natural environments: swamps, open water, meadows, reed beds or even wet woodlands. Many plant and animal species have made it their home, including rare and remarkable specimens. The marsh is also a place of fishing, hunting and walking for locals and tourists. It also provides services to the community by serving as a zone of flood expansion and low-flow support in times of drought. Finally, it filters the water that used to supply collection wells, which are now out of service. But with the development of vegetation and the presence of numerous drains drying up the marsh, the site was in peril and risked losing all of its assets. Also important works were carried out: brush clearing, plugging of the drains and rewinding of the stream. The work was completed at the end of 2020. With the first rains, we are already seeing the expected results. The water comes to the surface, floods the wet meadows and gradually flows into the marsh.
Another example in Ardèche : the preservation of the wetlands of the Source of Vernet Prades. In 2020, the Rhône-Alpes Conservatory of Natural Areas, the Société Générale des Eaux de Sources Minérale (SGESM) and the Monts d’Ardèche Regional Natural Park signed a 3-year partnership. Objective: to ensure both the quality of the water resource and the preservation of the woodlands and wetlands surrounding the source of Vernet. This work is part of a collaboration set up at the national level between the Agromousquetaires pole and the CEN network.
Preservation of the wetlands of the Source of Vernet Prades
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© Conservatory of natural spaces Rhône-Alpes.
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In the Drome, at the gates of Montélimar, near Châteauneuf-du-Rhône, is a wetland, the Rhone Islands ponds. Subsisting in the heart of a landscape shaped by the developments, these environments play an essential role for the sustainable development of the territory: island of freshness, biodiversity reserve, area for walking, fishing, etc. Indeed, these wetlands provide us with many services, a better quality of life and this for free! But these ponds are getting poorer and degrading. Also an ambitious restoration project has been set up to preserve these natural spaces, associating actors and local elected officials. Led by the Conservatory, the work will begin in spring 2021 and will focus on reconnecting the ponds to each other and to the Rhône river. On the one hand, to promote the flow of water and nutrients necessary for the development of biodiversity. On the other hand, to create areas of refuge and interest for wildlife (pike, minnow, kingfisher, beaver, etc.). Today’s steep banks will also be reshaped and vegetated to make room for reed beds and wet woodlands. The goal? Promote the diversity of environments and the reception of wildlife.
Restoration of the ponds of the Rhône islands in Châteauneuf-du-Rhône
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© Conservatory of natural spaces Rhône-Alpes.
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In the Loire, the Monts du Forez constitute a real water tower for the Loire department. The revision of the “departmental inventory of peatlands of the Loire” showed that 52 peatlands for approximately 850 hectares are currently listed on the Loire side of the massif. This makes this area one of the largest peat bogs in France. These remarkable wetlands are the sources of many streams which feed the plain of Forez before flowing into the Loire.
Preservation of the wetlands of southern Forez, the Loire Gumières water tower – La Chapelle en Lafaye – Montarcher – Saint-Jean-Soleymieux
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© Conservatory of natural spaces Rhône-Alpes
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In the south of Forez, these wetlands at the head of the watershed are characterized by their high concentration and diversity. There are peaty areas, wooded peat bogs and lots of wet meadows. These environments are mostly fed by rainwater and springs, which in turn feed the streams downstream. In consultation with the owners and local elected officials, the Conservatory of natural spaces preserves five sites in this sector. In particular a wet meadow of 2.4 hectares in the town of Saint-Jean-Soleymieux. Grazed part of the year by cows, a solution has been found to preserve the quality of the water in the stream that runs through the plot and allow the herd to water at the same time. Thus, the Conservatory installed fences along the river and two drinking troughs. These are connected to the stream: they are fed by it and replenished by the water not consumed.
Preservation of the Marais de Morlin, one of the last marshes of the Rhône in Taluyers
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© Conservatory of natural spaces Rhône-Alpes
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The Morlin marsh is located in the south of Rhône department (commune of Taluyers), on the Mornant plateau. Through its ponds and its vegetation, the Morlin marshes store and purify the water which crosses it. It thus plays an important role in regulating floods: in the event of heavy rains, water is absorbed in the marsh (there is a peak at the level of the piezometers, responsible for measuring the water level). That makes so much less water around! Since 1998, the Morlin marshes have been grazed by Charolais from a local breeder. This resumption of exploitation was very beneficial: it slowed down the dynamics of the vegetation and allowed herbaceous plants to survive. Without it, there would only be willow woods and thickets! The site is a joy to the many walkers and inhabitants who come to discover the marsh and its natural curiosities, on the occasion of organized outings.
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