Stream bottom resistivity tomography to map ground water discharge

Area of Science:

• Geophysics
• Hydrology
• Environmental Science

Background:

• Understanding groundwater/surface water interactions is vital for stream water quality and ecosystem function.
• Direct current electrical resistivity (DCER) offers a potential method for assessing these interactions.

Purpose of the Study:

• To investigate the effectiveness of DCER for mapping groundwater discharge zones in streams.
• To characterize subsurface heterogeneities influencing stream-aquifer exchanges.

Main Methods:

• Conducted underwater electrical resistivity surveys along a 107-m stream section.
• Utilized tile probing and resistivity test box analysis for data validation.
• Compared resistivity data from low-stage and high-stage stream conditions.

Main Results:

• Identified three distinct resistivity layers: streambed sediments, residual clays, and carbonate bedrock.
• Mapped groundwater seeps where residual clays were thinnest and bedrock closest to the streambed.
• Observed changes in pore fluid conductivity and resistivity variations indicative of surface water infiltration and groundwater discharge.

Conclusions:

• DCER is effective for mapping groundwater discharge zones at the meter scale.
• Resistivity data under varying stream stages can delineate areas of groundwater seeps and surface water infiltration.
• The study highlights DCER's utility in characterizing subsurface heterogeneities driving stream-aquifer exchanges.