CONTRIBUTION OF CORRELATION AND SPECTRAL ANALYSES TO THE REGIONAL STUDY OF A LARGE KARST AQUIFER (CHARENTE, FRANCE)

The purpose of the study is to demonstrate that correlation and spectr al analyses can contribute to the regional study of a large karst aqui fer. An example is presented for the La Rochefoucauld karst aquifer (C harente, France). Different types of spatially distributed time series provide valuable spatio-temporal information for the karat aquifer. T he available time series consist of the spring flow rates, the flow ra tes at different locations in sinking streams, the piezometric levels, the electrical conductivity and temperature of the water, the atmosph eric pressure and the precipitation The analysis of the flow rates at the springs shows that the aquifer empties very slowly and has a large storage capacity. Hydrodynamic links were established between three o f the four rivers flowing on the aquifer and the springs. The results also demonstrate the important spatial heterogeneity of the aquifer an d indicate that the most rapid flow occurs in the northern part of the aquifer. Hourly piezometric and electrical conductivity time series i ndicate that the transmissivity of the aquifer varies when some conduc tive channels become desaturated during the low water period. The dela ys between the distributed recharge and the piezometric level, between the localized river input and the how rates at the springs and betwee n the electrical conductivities in rivers and the main spring provide information on the travel times in the aquifer, The observation of ear th tides and barometric effects indicate that this apparently unconfin ed aquifer has a confined behaviour. (C) 1998 Elsevier Science B.V. Al l rights reserved.