Year of Award
2026
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Geosciences
Other Degree Name/Area of Focus
Hydrogeology
Department or School/College
Geosciences
Committee Chair
Payton Gardner
Commitee Members
Andrew Wilcox, Zachary Hoylman
Keywords
hydrogeology, mountain front recharge, mountain block recharge, recharge, MODFLOW, groundwater model
Subject Categories
Geology | Hydrology | Water Resource Management
Abstract
Mountain Front Recharge (MFR) is a critical recharge source for alluvial basin aquifers throughout the Intermountain West, yet the spatial and temporal dynamics of distinct recharge pathways remain poorly constrained. This study investigates the seasonal and spatial dynamics of MFR pathways and evaluates their impact on the Missoula Aquifer, a sole-source alluvial aquifer in western Montana, USA. MFR includes both surface-water inflows from mountain areas and Mountain Block Recharge (MBR), the groundwater contribution to the basin aquifer. A valley-scale water balance was employed to estimate first-order contributions and temporal fluctuations of MBR flow paths. A three-layer steady-state MODFLOW groundwater model was used to quantify recharge pathway magnitudes and their spatial distribution. Results indicate that the Missoula Aquifer operates near equilibrium over annual to decadal timescales with strong seasonal storage cycling. Groundwater model results show that MFR is a dominant recharge source to the aquifer, with Focused Mountain Block Recharge (FMBR) contributing approximately 37% of total recharge and Surface Mountain Front Recharge (SMFR) contributing approximately 15%. FMBR was concentrated along steep alluvial corridors at major valley inlets and remained relatively stable over time, while Diffuse Mountain Block Recharge (DMBR) contributions (~2%) were comparatively minor and could not be distinguished from zero given the associated uncertainty. These findings demonstrate that mountain-derived recharge is critical to sustaining the Missoula Aquifer and that shallow, spatially concentrated recharge pathways dominate mountain-to-basin groundwater exchange in this system. This work improves understanding of mountain-basin groundwater connectivity and highlights the importance of explicitly representing distinct MFR pathways in basin-scale groundwater assessments.
Recommended Citation
Bollag-Miller, Mikaela, "Spatiotemporal Dynamics of Mountain Front Recharge Flow Paths and Their Contribution to Alluvial Aquifer Water Supply" (2026). Graduate Student Theses, Dissertations, & Professional Papers. 12770.
https://scholarworks.umt.edu/etd/12770
Previous Versions
© Copyright 2026 Mikaela Bollag-Miller