John Wilson and Huade Guan
Groundwater hydrologists commonly consider and study the contribution of mountains to groundwater basin recharge at the mountain-front, while hillslope hydrologists often only focus on the thin soil layer above the bedrock surface. At mountain hillslopes, few studies have examined the partitioning of water between shallow processes (ET, interflow, etc) and deep percolation to the mountain block.
At least in some cases, the mountain bedrock carries a significant amount of water to adjacent basins. Variably saturated numerical simulations are conducted at the hillslope scale to help understand how water partitions at the soil-bedrock interface. Fractured rocks are described as a continuum with composite hydraulic functions for both fractures and matrix. We address three questions: (1) What is the permeability threshold above which percolation through bedrock becomes significant, and how is this compared to the actual fractured rock permeability? (2) What is the effect of bedrock surface topography (slope and depression) on water partitioning at the soil-bedrock interface? (3) What is the effect of soil characteristics on water partitioning?