Barrages de tufs calcaires et cascades dans le Centre-Var?: rapport avec les eaux des sources karstiques, historique et déclin actuel

摘要

In the valleys of inner Provence, numerous travertine formations are wide extension in relation with important karstic springs. Because the geomorphological evolution, the old travertines are maked up balconies and terraces. The recent period of main travertine construction begins as far back as in the Preboreal (even in B?lling at southern Luberon) and appears generalized in the Atlantic. In the late Neolithic (around 4000?BP), this sedimentation decreases with the climatic deterioration and the opening of forest cover under the weight of human pressure. However some tufa dams (stromatolite doms) and associated wetland with peat deposits continues up to the historic times. In the Middle Var County, these tufa deposits on the dams remains active in some refuge sites, in the upper and woody valleys, near the karstic springs, and in any high waterfalls. More along the rivers, some waterfalls with tufa deposits proceeds from the old mills and irrigation canal fitting. This tufa sedimentation is in relation with the interference of multiple factors, whose:-?carbonate mineralization of the karstic springs,-?seasonal working of the hydrosystem,-?regional and local ecosystem (forested land, important riparian cover),-?algo-bryophitic biotope.Nowadays, the stromatolitc sedimentation is in critical situation because the impact of multiple factors in relation with increased urbanization and environmental change:-?river pollution, increased turbidity in little tributaries flowed from agricultural mecanization,-?decreased flow in seasonable times (spring - summer), the most favourable to the algo-bryophytic activity, because the common increasing water sample.The recent drought period (2006-2008) has maked worse these impacts on the tufa dams. And the protection of these sites of large environmental and patrimonial interest put complex problems.