An alternative to traditional seepage meters: Dye displacement

Abstract

A new seepage meter design that increases sensitivity to the small hydraulic gradients that drive submarine groundwater discharge was developed as an inexpensive alternative to traditional seepage meters. The new design replaces seepage meter bags with open‐ended tubing through which the displacement of injected dye is a highly reproducible measure of discharge. Laboratory measurements, detailed mathematical modeling of groundwater flow around seepage meters, and parallel field tests of bag and dye displacement seepage meters demonstrated that the new design can improve the precision and temporal resolution of submarine groundwater discharge measurement. In parallel field tests, groundwater discharge to 15 cm diameter, bag‐equipped seepage meters was half of the discharge to adjacent 15 cm diameter dye displacement seepage meters. Model results confirm that similar discrepancies, caused by groundwater diversion around bag‐equipped seepage meters, may occur during the deployment of 57 cm diameter seepage meters in common field conditions. A second field deployment of 15 cm diameter dye displacement seepage meters showed saline inflow into sandy sediments at high tide and a high rate of discharge at low tide, similar to observations made with far more expensive, open flow path automated seepage meters in other studies.