42-11 Investigation of Tidal-Bore-Induced Surface Water and Hyporheic Zone Mixing Using Paired Geophysics and Heat as a Hydrologic Tracer

Abstract:

Tidal bores are progressive waves induced by flood tides funneled into narrow coastal rivers. They create powerful turbulent waves that drive sediment transport and mixing of heat, nutrients, salinity, and other surface water constituents. These conditions strongly influence ecosystem productivity and estuarine fluvial geomorphology. Despite their importance, tidal-bore mixing processes in integrated channel-hyporheic zone systems have received relatively little research attention because bores are uncommon, localized, and potentially hazardous to work in.

The Bay of Fundy borders the state of Maine and the Canadian Maritimes and is home to among the world’s highest tides. The Salmon River, a 40-kilometer estuary that empties into the Bay of Fundy’s Cobequid Bay, is a dyked, macro-tidal river that experiences semi-diurnal tidal bores. During high tides, seawater propagates upriver against the natural freshwater flow direction. To investigate tidal bore mixing in the surface water column and underlying sediment, a 500 m reach of the estuary was instrumented with conductivity-temperature-depth loggers (Solinst LTC), water temperature loggers (RBR SoloT, Onset Hobo Tidbit), and vertical sediment temperature probes (iButtons installed at multiple depths in stakes). These sensors were installed in cross-shore and longitudinal channel directions to characterize the spatiotemporal temperature patterns throughout the reach and were programmed to record at relatively high frequencies. These water temperature time series were complemented with water temperature maps collected from a drone-based thermal infrared survey to observe the bore arrival (DJI Matrice 300 UAV equipped with a Zenmuse H20T sensor). Frequency-domain electromagnetic geophysical surveys (Geophex GEM-2) were also conducted to map resistivity patterns and infer mixing dynamics. All data were recorded in the late summer 2026 during spring tides, when the bore was most pronounced, and during warm atmospheric conditions to maximize the thermal contrast between the Bay of Fundy and the Salmon River. These recently collected data will be presented to highlight our preliminary interpretation of the bore mixing dynamics in the channel and hyporheic zone as well as the implications for physical and biogeochemical processes in this distinctive, macrotidal setting.

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