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OS1q Hydrological diagnosis and forecasting: complex aquifers

abstract 611

Active water management resources of karstic water catchment: the example of Le Lez spring (Montpellier, South France)

Author(s): Nathalie Dörfliger, Hervé Jourde, Bernard Ladouche, Perrine Fleury, Patrick Lachassagne, Séverin Pistre, Arnaud Vestier
Nathalie Dörfliger1, Hervé Jourde2, Bernard Ladouche1, Perrine Fleury1, Patrick Lachassagne1, Séverin Pistre2, Arnaud Vestier3 1 BRGM, Water Division, RMD Unit, 1039 rue de Pinville, F-34000 Montpellier, phone + 33 4 67 15 79 65; fax + 33 4 67 64 58 51

Keyword(s): water management, Mediterranean basin, Karst aquifer

Article:

Poster:

Session: OS1q Hydrological diagnosis and forecasting: complex aquifers

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.

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Active water management resources of karstic water catchment: the example of Le Lez spring (Montpellier, South France)