IWRA Proceedings

AbstractIn Mediterranean karst groundwater has potentially important reserve which represents a high interest for the future in numerous countries under global and climatic changes. Karst groundwater resource is the centre of dynamic processes determined by input with rainfall and water losses of river and by output (Pinault et al., 2001). Karst groundwater environment is characterised by heterogeneity and consequently, classical hydrological model at catchment scale is not appropriated. Either double continuum model is developed integrating hydrodynamic parameters distribution of the aquifer or lumped model is used, such as inverse modelling approach based on the determining of transfer function on the whole hydrological cycle allows reproducing the hydrological behaviour of such system, and such as reservoirs model (Fleury, 2005 ; Fleury et al, 2007). Then, karst water is generally captured for water supply at the level of their springs; due to the important temporal variations of spring discharges, water pumping through boreholes intercepting the water saturated karst conduit allows to carrying out an active management: higher rate of pumping than the low water stage discharge of the system under natural condition during low water period, as the reserve of the system will recover rapidly during the recharge period. The karst system of the Lez, used for the water supply through an active water management for Montpellier is presented as a study case. The Lez karst system is one of the rare site where an active water management is carried out. As it is a Mediterranean karst system, such karst system is sensitive to extreme events such as Cévennes events (heavy rain during a short period of time on a restrictive area). According namely to the degree of water saturation of the system, the intensity of flooding of the Lez river downstream of the spring will be of various intensity (Roesch et Jourde, 2007). The aim of this study is (i) to summarize the knowledge concerning the karst hydrogeology of this aquifer based on geology and recent reinterpretation of seismic profiles and on the update interpretation of water level and discharges time series, (ii) to present results of recent studies concerning the demonstration of the effect of the active water management on the hydraulic functioning of the system, and (iii) to simulate with two types of model various scenarios of pumping rate (duration, period) for different climate conditions considering technical exploitation constraints, in order to assess the possible mitigation scenario of flooding in an urban area such as Montpellier. Such active water management may be also a new challenge for a pluri-objective management of a system integrating socio economic issues, environmental issues and flood mitigation.