2 Advances in characterizing groundwater, surface water, and their interactions

This session focuses on characterizing groundwater, surface water, and their interactions through fieldwork, modeling, and data synthesis. We welcome submissions addressing flow, transport, water quality, and water levels under both typical and extreme conditions.

Sunday, 22 March 2026
8:00 AM - 12:00 PM
CCC, Room 25

Groundwater-Surface Water Interactions in the Delaware Bay: The Role of Current-Bedform Interactions and Density-Driven Flow Processes

Paper number: 2-7
Program: Technical Sessions
Time: 10:00 AM – 10:20 AM

Authors

  • Madelaine Reid Presenting Author
    University of Massachusetts Lowell , Lowell, MA
  • Neshat Movahedi
    University of Massachusetts Lowell , Lowell, MA
  • Li
    Delaware River Basin Commission , West Trenton, New Jersey
  • Adam Skarke
    Mississippi State University, Mississippi State, MS
  • James Heiss
    University of Massachusetts Lowell, Lowell, MA

Abstract

Biogeochemical processes in estuarine sediments mediate nutrient loads to marine ecosystems. The biogeochemical processes are supported by benthic exchange, which delivers nutrient- and oxygen-rich surface water into subsurface sediments. While benthic exchange has been quantified extensively in terrestrial freshwater and marine environments, we have little understanding of benthic exchange processes in estuaries. In this study, we investigate vertical water and chemical fluxes across the sediment-water interface in the Delaware Bay by applying a novel numerical modeling approach involving nested surface water and groundwater models. Outputs from surface water models are one-way coupled to a variable-density groundwater flow and salt transport models built with the USGS SEAWAT modeling code. The groundwater models capture the influence of tidal current reversals and surface water salinity fluctuations on groundwater flow patterns and salinity distributions in estuarine sediments. Model results show that groundwater flow paths in estuary bedforms are strongly affected by fluid density contrasts in pore water. Surface water of elevated salinity infiltrates the estuary bed and mixes with upwelling fresh groundwater. The ensuing fluid density contrasts in bedform sediments lead to density instabilities and downward convection of salt. Vertical freshwater and saltwater fluxes across the sediment-water interface are highly dynamic owing to the combined influence of current-bedform interactions and buoyancy-driven flows. Lastly, the models show that the influence of fluid density contrasts on exchanges decreases up the estuary as freshwater becomes more prevalent. These insights are important for quantifying how estuarine groundwater-surface water exchanges affect chemical fluxes to downstream marine ecosystems.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411431

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