PNNL

Abstract

A flux detection probe (FDP) was designed to quantify hyporheic zone groundwater surface water (GW-SW) exchange under dynamic and steady state flux conditions. Currently available instruments focus on estimating either vertical pore water velocity or Darcy flux. Both of these parameters must be understood to evaluate residence time and mass flux of constituents. Furthermore, most instruments are not well suited for monitoring instantaneous velocity or flux under dynamic exchange conditions. Our probe design uses electrogeophysical measurements to estimate in-situ sediment porosity which allows us to convert pore water velocity to Darcy flux. Dynamic pore water velocity is obtained by monitoring fluid conductivity and temperature along the FDP probe. Pressure sensors deployed at the top and bottom of the probe provide the additional information necessary to estimate vertical permeability. This study looks at the performance of the individual functions of the FDP probe within a controlled soil column where simulated river water displaces simulated GW. The FDP probe was able to match the true pore water velocities using natural tracer breakthrough curves to -1.7% of the theoretical values and match the porosity of the soil to range of -3.2 to 1.5% of values from packing parameter. Also, theoretical flux values matched predicted values under both steady state and dynamic conditions.