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

Abstract

[1] 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.

What controls the partitioning between baseflow and mountain block recharge in the Qinghai‐Tibet Plateau?

“…There is typically high uncertainty in estimating the partitioning of recharge between baseflow and MBR due to multiple controlling factors. Theoretical modeling studies have demonstrated that typically 5 to 20% of recharge becomes MBR and that it is plausible for up to 40% to become MBR [Gleeson and Manning, 2008;Welch and Allen, 2012]. The significant controls on MBR include specific characteristics of mountain topography, particularly depth of stream incision which governs the groundwater flow path, the ratio of recharge to hydraulic conductivity which governs water table elevation, and the vertical distribution of hydraulic conductivity in the mountain block which governs the depth of groundwater circulation [Gleeson and Manning, 2008;Jiang et al, 2009;Welch and Allen, 2012].…”

“…MBR is the groundwater discharge from the mountain block to the aquifers of downgradient alluvium [Manning and Solomon, 2003;Welch and Allen, 2012;Wilson and Guan, 2004]. There is typically high uncertainty in estimating the partitioning of recharge between baseflow and MBR due to multiple controlling factors.…”

“…Groundwater systems in mountain terrain control two important contributions to the water resources of downstream alluvial plains: the baseflow of the mountain streams and mountain block recharge (MBR) [Welch and Allen, 2012]. MBR is the groundwater discharge from the mountain block to the aquifers of downgradient alluvium [Manning and Solomon, 2003;Welch and Allen, 2012;Wilson and Guan, 2004].…”

“…Theoretical modeling studies have demonstrated that typically 5 to 20% of recharge becomes MBR and that it is plausible for up to 40% to become MBR [Gleeson and Manning, 2008;Welch and Allen, 2012]. The significant controls on MBR include specific characteristics of mountain topography, particularly depth of stream incision which governs the groundwater flow path, the ratio of recharge to hydraulic conductivity which governs water table elevation, and the vertical distribution of hydraulic conductivity in the mountain block which governs the depth of groundwater circulation [Gleeson and Manning, 2008;Jiang et al, 2009;Welch and Allen, 2012]. Other studies using realistic models of specific mountainous regions have found that roughly 20% to 30% of recharge becomes MBR and also demonstrate that the theoretical controls on MBR/baseflow partitioning identified in the generic model studies generally apply in more realistic mountain settings as well [Ball et al, 2014;Manning and Solomon, 2005].…”

Interaction of various flow systems in small alpine catchments: conceptual model of the upper Gurk Valley aquifer, Carinthia, Austria

“…In the small-scale structured environment of mountain catchments, springs or groundwater wells that drain different flow systems can occur in close contact to each other (Hilberg and Kreuzer 2013). Groundwater flow in alpine valleys occurs in two completely different but possibly interacting kinds of aquifers (Welch and Allen 2012). Usually, unconsolidated sediments in the valley floor provide porous aquifers.…”