Partially penetrating lake-aquifer interaction in a laboratory-scale tidal setting

Freshwater lakes close to the coast are important ecotones with strong functional dependency on ocean forces. Tides are likely to create dynamic lake-groundwater interactions, which have not been previously assessed for partially penetrating lakes. This study investigates tidal lake-groundwater interaction in a laboratory-scale aquifer cross-section with and without the existence of a partially penetrating lake. Experimental observations were found to be well matched to the results of numerical modeling in terms of the amplitudes and phases of pressure fluctuations at 19 locations. The results show that the lake dampened tide-induced pressure head fluctuations, indicating that the enhanced storage capacity was more influential in modifying tidal propagation relative to the increased transmissiveness imparted by the lake. The lake also caused stronger depth-dependency in groundwater tidal fluctuations, as determined from vertical profiles of tidal amplitude and phase. Vertical profiles also reveal that the tidal amplitude and phase responded differently to the addition of the lake, in a manner that reflects previous studies of tidal propagation in layered aquifers. Tides created significant aquifer-lake fluxes, leading to strong rates of lake flushing, particularly through the seaward lake boundary. Including a clogging layer at the lake bottom (within numerical models) tended to reduce the lake's effects on tidal propagation, although clogging layer effects were complex. This study highlights the important role of tides on partially penetrating lake-groundwater exchange dynamics and the influence of partially penetrating lakes on tidal propagation in coastal settings, albeit at the laboratory scale.