Time series analyses for Karst/River interactions assessment: Case of the Coulazou river (southern France)

In many karst systems throughout the world, numerous karst features facilitate the exchange of water between the surface, the vadose zone and the saturated zone of the aquifer. These interactions play actually a prominent rote in the ground and surface waters circulation. This study aims at assessing Karst/River interactions by the way of flood hydrograph analysis and new toots for time series analysis in this field of research. As in many others binary karst system the captured waters of the Coulazou river travel through conduits and preferential flow paths in the vadose zone, and join the saturated zone of the aquifer. This river is an ephemeral river in a Mediterranean context where rapid and intense floods occur each year. This hydrologic behaviour is appropriate to study the transfer of a flood through a karst area. The water level in caves, the rainfall all over the karst aquifer catchment area, the piezometric level within the karst aquifer and the discharge in the river upstream and downstream of the karst aquifer are measured in order to understand the Karst/River exchanges. During a flood the modification of the surface flows in the river is treated as a Linear Time-invariant system (LTI system). Correlation and spectral. analyses are used to understand how the LTI system dissipates or enhances the flood wave energy. For several floods, the frequency response function estimations are interpreted in term of flood wave modification through the karst area. In this way, according to the initial state of the Karst/River system, the autogenic and/or allogenic recharge of the aquifer may induce surge flows and a significant karst contribution to surface flows. (c) 2007 Elsevier B.V. All rights reserved.