In Phase 1, subproject P1 started to study how tides, waves and beach morphodynamics affect transient groundwater flow and transport on different spatio-temporal scales. In Phase 2, we will specifically address the role of the foreshore wave transformation on morphodynamics and associated groundwater flow and transport as well as the effect of major stormfloods on infiltration rates and subsurface salinities at our core field-site at Spiekeroog. We will further assess the transferability of our Spiekeroog findings regarding the relationship between frequency and amplitude of morphological changes and groundwater salinity, age and temperature patterns at two validation sites (De Panne and Truc Vert). Our methods include beach and foreshore morphology surveys using camera imaging, laser-scanning and drones in combination with numerical models to derive typical adaptation time- and length scales of the beach morphology. Geophysical methods will continue to identify subsurface salinity patterns and their change over time. We will further use environmental tracer data to estimate subsurface residence times. Morphological, hydro(geo)logical and geophysical data from all field sites inform numerical groundwater flow and transport modelling to provide a comprehensive and generalizable picture of the subsurface of high-energy beaches. This knowledge on the distribution of water bodies, flow velocities, residence times and extent of mixing from all three sites will provide the basis for biogeochemical investigations carried out in subprojects P2-P6 and inform global modelling in the new subproject P7.