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Role of Mediterranean karst aquifers in flood genesis, Does an active management of karst system could contribute to reduce the risk of flooding or can we predict by simulations its behaviour?


Dörfliger Nathalie

Karst, a typical landscape on limestone and/or dolomite rocks that are soluble, covers a large part of the Mediterranean basin. These rocks have specific aquifer properties, due to their evolution into karst under the combined effect of groundwater flow within cavities and of the chemical dissolution. They are characterized by a dual flow system consisting of a fissured system which represents the bulk mass of permeable limestone, and a conduit system with the karst conduits network. Exchange between the two systems is controlled by hydraulic head differences as well by the hydraulic conductivities and the geometric setting. Outlets of karst system may be at the origin of a runoff catchment basin of a river. The hydrology and hydraulic of the river may be conditioned by the upstream groundwater reservoir and its management.
Heavy rainfall in Mediterranean climate and high intensity rainfall period of short duration (few hours until 24hours, or 2days) on very limited extension contribute to generate flooding. Serious damages with namely severe people injuries and loss of lifes may occur. If runoff takes place within the catchment basin, the karstified limestone may also absorb part of rainfall; due to the characteristics of flow within karst aquifers, flash flooding may be important in volume and dynamic.
Which events may provoke flooding, considering the water saturation level of the saturated zone and as well, of the epikarst reservoir, if it is present? Methodology of characterizing events and water level time series of piezometers or of springs is developed and applied on various Mediterranean sites. In one hand, karst aquifers may contribute to flood when the karst fast flush flooding phenomenon takes place and in the other hand, may contribute to the mitigation of the floods, considering either the groundwater reservoir state and also the management by pumping of the karst system.