Sample Functions as Indicators of Aquifer Heterogeneities

An adaptive slope matching method is used to evalute the aquifer heterogeneity from constant rate aquifer test data. The basic aquifer parameters such as the storativity and transmissivity are considered to vary spatially and the effects of such changes appear as temporal variations during a pumping test period. It is stressed that this is due to the depression cone expansion with time around the pumping well. The plots of individual parameters versus time are referred to as the sample functions. These functions have erratic variations indicating that the aquifers considered in this study have local heterogeneities. Furthermore, a moving average technique is applied to each parameter sample function for the purpose of finding regional trends in the parameter variations. It is interesting to notice that the arithmetic average values of sample functions yield aquifer parameter values as obtained by the classical type curve matching techniques which assume that the aquifer concerned is homogeneous. Hence the use of the sample function concept is recommended for the detailed interpretation of the aquifer heterogeneity.