Vertical trend analysis of equivalent hydraulic conductivity in alluvial fan gravel deposits considering open void connectivity

Abstract

This study demonstrated groundwater flow simulations to investigate a vertical trend of equivalent hydraulic conductivity of alluvial fan gravel deposits in Sapporo, Japan, considering open void connectivity. Equivalent hydraulic conductivity was defined according to Darcy’s Law for a cube of 10 m in size, consisting of one million cells assigned among fully packed (without open voids), loosely packed (with less-connected voids) or very loosely packed (with well-connected voids) deposits. The stochastic generation was performed under each configuration in terms of target depth sections for vertical trend analysis, and horizontal variogram ranges (random, high, and low connectivity, and no open voids) for open void connectivity. The logarithmic average of 100 equivalent hydraulic conductivities was calculated in each configuration, and the vertical trends were determined. The simulation results showed that the equivalent hydraulic conductivity increased when the open void frequency was large in the shallow zone and the connectivity of the open voids was assumed. In particular, the high connectivity assumption was needed to match the in situ trend with a decay exponent of 0.05 m^–1. Modeling the vertical trend with such a large decay exponent was essential to obtain realistic solutions of the groundwater flow and transport system in the alluvial fan.