A Device for Measuring Groundwater Velocity in the Capillary Fringe

Abstract

Groundwater flow in the capillary fringe is rarely measured during hydrogeological studies because of the difficulties associated with investigating this region. Previous research using a point velocity probe (PVP) to investigate groundwater velocity below the water table suggested that the PVP may also be capable of measuring groundwater velocity within the capillary fringe. The earlier PVP was redesigned for this study to allow for groundwater velocity data to be collected remotely. Using this system, groundwater velocity in the capillary fringe was investigated under field and laboratory conditions. Field experiments to investigate horizontal flow in the capillary fringe were conducted either by collecting vertical velocity profiles across the water table, or by holding the probe stationary and allowing seasonal recharge to move the capillary fringe and water table past the probe. Laboratory experiments were conducted in a controlled flow tank that simulated regions of an aquifer up to 85 cm above the water table. The redesigned PVP performed well as a remote system and provided velocity measurements up to 12 cm above the water table under field conditions. These values were consistent with those measured below the water table. In the laboratory, under conditions of drainage, groundwater velocity measurements in the capillary fringe consistent with values below the water table were measured up to 44 cm above the water table. The ability to measure horizontal flow of groundwater in the capillary fringe may open up new avenues for research in the study of contaminant transport in phreatic aquifers.