Sensitivity of stream-aquifer seepage to spatial variability of the saturated hydraulic conductivity of the aquifer

In this paper. the sensitivities of stream-aquifer seepage flow and the state of connection or disconnection between stream and aquifer, to spatial variability in the aquifer-saturated hydraulic conductivity, are studied with the variably saturated modelling programme, SWMS_2D, using a Monte Carlo technique. A simple stream-aquifer flow system is used with a rectangular stream. with a clogging layer on its perimeter, partially penetrating an alluvial aquifer. A 2D nearest-neighbour method is used to Generate fields of log normally distributed saturated conductivity for the alluvial aquifer for a specific set of degree of heterogeneity and the nearest-neighbour autoregressive parameters. Seven different cases are studied. Five of these investigate the effect of the nearest-neighbour parameters, and three cases investigate the effect of aquifer water table level. The results show that the nearest-neighbour parameters and the aquifer degree of heterogeneity significantly affect the modelling of stream seepage, pressure heads and the state of connection/disconnection between stream and aquifer, particularly when the water table is some distance below the streambed. Moreover, comparisons of these results with a purely deterministic model show good agreement when the stream and the aquifer are connected or disconnected but with a high water table. However, there are significant differences between the deterministic and stochastic models when the water table is well below the streambed. (C) 2004 Elsevier B.V. All rights reserved.