How does subsurface characterization affect simulations of hyporheic exchange?

Area of Science:

• Geosciences
• Hydrology
• Geophysics

Background:

• Subsurface architecture influences water flow and solute transport.
• Accurate modeling of hyporheic zones is crucial for understanding stream-aquifer interactions and biogeochemical cycling.

Purpose of the Study:

• To investigate how detailed geologic structures (subsurface architecture) improve predictions of streambed flux and hyporheic residence time distribution (RTD).
• To assess the impact of geophysical methods, particularly electrical resistivity (ER) imaging, on characterizing subsurface properties and flow/transport.

Main Methods:

• Simulated five subsurface realizations with increasing geologic detail.
• Utilized particle tracking to generate RTDs.
• Employed electrical resistivity (ER) imaging and time-lapse ER imaging during a solute tracer study to inform model calibration.

Main Results:

• Calibrated models using transient ER data showed streambed flux estimates three orders of magnitude higher than uncalibrated models.
• Median residence times decreased from 10^3 hours (uncalibrated) to 10^0 hours (calibrated).
• More resolved subsurface architectures resulted in wider RTDs, indicating complex hyporheic flowpaths.

Conclusions:

• Geophysical measurements, especially ER imaging, are valuable for realistic simulation of hyporheic flow and transport.
• Improved characterization of lithological boundaries and calibrated hydraulic conductivity significantly affect model predictions.
• Detailed subsurface architecture enhances understanding of hyporheic zone dynamics and their role in biogeochemical processes.