Size and shape sorting in a Dutch tidal inlet

Abstract

ABSTRACTA tidal inlet system with an outer tidal, delta, situated between two barrier islands along the north coast of Holland was studied for size and shape sorting. With size data different sand types can be distinguished and in individual samples distinct grain populations can be recognized in some cases. Graphs of shape values, plotted against the size intervals of samples also reveal the presence of different grain populations, together with their genetical significance.The following conclusions could be drawn.There is no sand transport directly from island to island. Sand up to 400 μm enters the tidal inlet, is sorted out in the tidal flat area and partly re‐enters the sea via the outer tidal delta. On the delta, the sediment is split up again in different populations. A lag deposit is left behind on the frontal part of the delta. The rest of the sand either re‐enters the tidal inlet cycle or contributes to the beach building of the next island. In the offshore environment, sand movement by wave‐induced currents is restricted to the shallow zone. In deeper water, part of the sediment is relatively immobile and has preserved inherited characteristics from the early Holocene transgressive phase. In front of Ameland, fossil barrier‐face deposits‐are present, off Schiermonnikoog the sea floor contains old tidal channel deposits.