32 Hydrogeology

Added due to amount of discipline abstracts submitted.

Tuesday, 10 March 2026
1:30 PM - 5:30 PM
RCC, 106

Fractured Bedrock Controls on Hyporheic Exchange in a Nonperennial Stream Revealed by Time-Lapse Electrical Resistivity Tomography

Paper number: 32-8
Program: Technical Sessions
Time: 3:30 PM – 3:45 PM

Authors

Abstract

Nonperennial streams dominate global river networks and are becoming increasingly prevalent as climate change, land-use shifts, and rising freshwater usage transition perennial systems to intermittent flow. Much of the limited literature on nonperennial streams emphasizes ecological aspects rather than hydrological processes. Nonperennial streams frequently transition between flowing, ponded, and dry states, causing significant variability in hydrological fluxes within the shallow subsurface. Understanding how these transitions influence connectivity between surface water and the shallow subsurface remains a critical gap in nonperennial stream research.

 Traditional hydrological methods struggle to capture this variability due to their limited spatial resolution. To address this, we applied time-lapse electrical resistivity tomography (T-ERT) in conjunction with traditional methods, including a piezometer network for monitoring groundwater levels. By exploiting the relationship between subsurface electrical properties and hydrological conditions through repeated measurements, T-ERT enables the monitoring of dynamic saturation, flow, and solute transport. We applied this approach along a fractured bedrock nonperennial stream in Cincinnati, Ohio to characterize how bedrock fractures influence hyporheic exchange dynamics. Seasonal time-lapse monitoring combined with ERT-based solute injection experiments allowed us to evaluate how fracture networks regulate hyporheic exchange as the stream transitions among flow states.

 Our results reveal that fracture connectivity strongly regulates the vertical and lateral extent of the hyporheic zone, with preferential flow paths persisting through dry periods and reactivating during rewetting.  These findings demonstrate how fracture architecture and discharge variability jointly control water storage and movement in intermittently flowing streams. By integrating high-resolution geophysical imaging with hydrological observations, this study provides new insights into the mechanisms governing connectivity and storage in nonperennial systems. The T-ERT observations were essential for tracking these transitions, capturing subtle, but critical, changes in subsurface saturation that conventional methods could not resolve. This capability demonstrates the power of T-ERT as a diagnostic tool for monitoring dynamic hydrological systems and highlights its potential for broader application in diverse nonperennial settings. Our approach establishes a new framework for integrating time-lapse geophysics with hydrological observation, enabling improved representation of hyporheic exchange in models of nonperennial stream systems.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411851

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