Fontaine de Nimes karst system (France)

Multi-tracer investigations and modelling revealed the structure and preferential flow paths of the Fontaine de Nîmes karst system. The research demonstrated how groundwater storage can initially attenuate rainfall-runoff, but how aquifer saturation and rapid conduit flow can subsequently amplify flash-flood response. These findings led to a hydrogeological forecasting approach for karst floods.

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Location: Nimes city, Occitanie region, France

Elevation: 55 - 120 masl

Geology: Cretaceous limestone

Aquifer type: karst aquifer

Scientific question: " What is the role of groundwater during floods "

Fontaine de Nimes is par of SNO Karst and OZCAR research infrastructure

Location map

Key findings

Karst catchment and groundwater flow: hydrogeological investigations and multi-tracer experiments defined the structure and recharge area of the Fontaine de Nîmes system and identified preferential underground flow paths.
Groundwater contribution to flash floods: the 2005 events showed that the karst system can rapidly transmit newly infiltrated rainfall to the spring. After an initial rainfall event saturates the aquifer, its remaining storage capacity decreases, increasing runoff and flood response during a subsequent storm.
Karst as both buffer and flood amplifier: the aquifer can initially store and attenuate part of the rainfall, but once highly saturated, rapid conduit flow and limited storage can contribute to very rapid flooding.
Hydrogeological modelling for flood forecasting: a conceptual and numerical model of the karst response to rainfall was developed and used to create a practical forecasting approach for karst flash floods in Nîmes.