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Abstract
Water and sediment transport were measured and calculated during a two months period on three locations at a 3 km long tidal divide in the Danish Wadden Sea. The water transport was flood dominated in the largest channel, almost neutral in the smaller channel and ebb dominated on the tidal flat. The tidal currents were short and strong during flood tide and long lasting but weak during ebb tide at all three stations. This tidal asymmetry caused the net sand transport across the tidal divide to be flood directed on all three stations. During a storm surge the currents were ebb-directed persistently for 21 hours despite large variations in water level. Grain-size distributions infer that the net sand transport converges to the northeast, indicating a recent north-eastward (flood directed) migration of the tidal divide. The suspended sediment transport during a tidal cycle is generally directed towards the north but on few special occasions the suspended sediment transport is southward directed because of resuspension of a nearby-located ephemeral blanket of sediment. The net temporal suspended sediment transport may be directed opposite the actual water transport during a tidal period. Depending on sediment availability, identical episodes of wind conditions showed different patterns of sediment transport. The results are the first published results from in situ measurements of transport of water and sediment across a tidal divide and are important in terms of understanding water and sediment transport patterns in estuaries.
