Consistency of groundwater flow patterns in mountainous topography: Implications for valley bottom water replenishment and for defining groundwater flow boundaries

Abstract

Topographic influences on groundwater flow processes that contribute to baseflow and mountain block recharge (MBR) are conceptually investigated using three‐dimensional numerical models of saturated groundwater flow. Model domains for conceptual and real topographies are developed as “mountain groundwatershed units” (MGUs) to represent regional‐scale watershed systems. Results indicate regularity in groundwater flow patterns that reflect consistency of prominent topographic features, providing a basis for conceptualizing three‐dimensional groundwater flow. Baseflow is generated mainly from recharge within the watershed area. MBR is produced primarily from recharge that is focused across triangular facets near the mountain front (∼73%–97% of total MBR), with additional contributions originating within the watershed (up to ∼27% of MBR). MBR contributions originating from recharge near the highest‐elevation watershed boundaries are minimal but are greater for topography with less stream incision. With orographic influences, more MBR originates within the watershed. MBR rates are relatively consistent between models because of similarities in mountain front topography, while baseflow is variable. Gains and losses to systems via cross‐watershed groundwater flux, generated because of topographic differences between adjacent watersheds, cause baseflow to vary by up to ∼10% but do not significantly influence MBR. In data‐sparse regions such as mountains, a basic numerical modeling approach, using the MGU concept with topography data and mapped watershed boundaries, can be used to develop site‐specific conceptual models to constrain water budgets, to delineate recharge areas, and to guide further investigation and data collection.