Effect of temperature variations on the travel time of infiltrating water in the Amsterdam Water Supply Dunes (the Netherlands)

Travel time is one of the important criteria in the design of managed aquifer recharge systems for securing good drinking water quality. Traditionally, groundwater travel time has been modelled without considering the effect of temperature. In this study, a cross-sectional heat transport model was constructed for the Amsterdam dune filtration system (in the Netherlands) to analyse the effect of temperature on groundwater travel times. A groundwater flow model, a chloride transport model, and a heat transport model were iteratively calibrated with measured groundwater levels, chloride concentrations, and temperature series in order to improve model calibration and reduce model uncertainty. The coupled flow and heat transport model with temperature-dependent density and viscosity provided more accurate estimation of travel times. The results show that seasonal temperature fluctuations in the source water in the infiltration pond cause temperature variations in the shallow groundwater. Viscosity is more sensitive to temperature changes and has a larger effect on groundwater travel times. Groundwater travel time in the shallow sand aquifer increases from 60 days when computed with the traditional groundwater flow model to 73 days in the winter season and 95 days in the summer season when computed with the coupled model. Longer travel time is beneficial for water quality improvement. Thus, it is important to consider the effect of temperature variations on groundwater travel times for the design and operation of managed aquifer recharge systems.