John Wilson, Huade Guan, and Laurel Goodwin
In arid and semi-arid climates, mountain front recharge (MFR) is a significant component of recharge to adjacent basin aquifers. Traditionally, MFR considers only the focused stream channel recharge at the mountain front, and assumes that the bedrock underlying the mountain block is impermeable, leading to a negligible diffuse recharge from the mountains. However, there is evidence for diffuse recharge in the mountains, at least for some locations. Bedrock permeability is one major controlling factor determining whether or not the diffuse recharge is significant. A good understanding of the role of mountain structure and bedrock geology on groundwater flow through the mountain block is a key to understanding the characteristics of MFR. Based on typical basin-and-range geology and saturated-unsaturated flow equations, archetypes of mountain blocks are numerically simulated considering the bedrock matrix and fractures, and faults. Different MFR patterns are observed for different mountain block archetypes. The results indicate a threshold bulk mountain block permeability needed for diffuse recharge.