The impact of hydrodynamics and texture on the infiltration of rain and marine waters into sand bank island sediments — Aspects of infiltration and groundwater dynamics

Interactions of different hydrological and geophysical processes on an emerging sand bank island are investigated focusing on the example of the Kachelotplate located west of Juist Island, southern North Sea. Measurements of groundwater levels, groundwater salinity, hydraulic conductivity of the sediment and the retention curve as well as the analysis of tide gauge and precipitation data from adjacent islands allow us to develop a conceptual model of the dominant hydrological processes. The main hydrological features are (i) dilution of the brackish groundwater caused by the positive water balance, (ii) infiltration of saline water due to sporadic inundation events during storm tides and (iii) limited lateral flow processes between seawater and groundwater driven by tidal conditions. Hence, from the hydrological point of view the future development of the Kachelotplate sand bank will strongly depend upon the inundation frequency of the sand bank island which will affect the development of a freshwater lens and hence of an environmental milieu suitable for plant development and therefore dune stabilisation.