WellSTIC: A Cost‐Effective Sensor for Performing Point Dilution Tests to Measure Groundwater Velocity in Shallow Aquifers

Abstract

Estimates of groundwater velocity are integral to any research or remediation project involving groundwater. In particular, understanding lateral groundwater flow in hillslope and mountainous systems constitutes a grand challenge in modern hydrology (Blöschl et al., 2019;Fan et al., 2019;Markovich et al., 2019). Addressing this challenge will require novel techniques to cost-effectively measure groundwater flow at remote field sites, but most modern groundwater velocity methods are expensive, labor-intensive and require vehicle access to a site.Traditional methods of measuring groundwater velocity fall into three categories: Darcy-based methods, interwell tracer tests and in-well techniques. Darcy-based methods measure groundwater velocity using Darcy's law and estimates of the specific discharge and effective porosity of an aquifer. These techniques are simple, but they require knowledge of the aquifer's hydraulic conductivity, which can vary over 13 orders of magnitude in natural media (Freeze & Cherry, 1979). Even geologically homogeneous aquifers can exhibit 10-100X variations in hydraulic conductivity over centimeter scales (Mackay et al., 1986;Sudicky, 1986). Though Darcy methods are simple, errors in hydraulic conductivity estimates can range multiple orders of magnitude, which result in large errors in groundwater velocity.In the second category of methods-inter-well tracer tests-a tracer is injected into an upgradient well while downgradient wells are monitored for tracer arrival. Of the various groundwater velocity techniques, natural

Mountainous Floodplain Connectivity in Response to Hydrological Transitions

“…The decay in electrical conductivity over time was used to compute the magnitude of the average linear groundwater velocity, assuming a point dilution shape factor of 2.36 (Hoppe, 2013). Complete details of these tests are described by Perzan and Chapin (2023).…”

“…Groundwater velocity in the gravel bed was measured by performing point dilution tests using the method of Perzan and Chapin (2023). First, drive-point piezometers were installed in three locations along a transect parallel to the river (Figure 1).…”

“…Each piezometer used a 15-cm screen length with the center of each screened interval installed 1.1 m below the soil-gravel interface. Inexpensive electrical conductivity sensors known as WellSTICs (Perzan & Chapin, 2023) were then used to perform two point dilution tests in August 2021. During each test, we first established a gas-free loop of re-circulating water between each piezometer screen and the surface.…”