Sediment transport in the Slufter inlet channel, Texel, The Netherlands
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Tidal inlets are a very dynamic coastal form. Sediment transport patterns and net sediment transport directions are of great importance with respect to tidal inlet stability. In this research, bedload and suspended load sediment transport and the factors governing this transport are investigated in the inlet channel of the small Slufter tidal inlet on the island of Texel, in the northwestern Netherlands. A triangular frame was place in the inlet channel, to which three Acoustic Doppler Velocimeters (ADV) for measuring flow velocity, three Optical Backscatter Sensors (OBS) for measuring suspended sediment concentrations and a wave gauge for measuring water levels and water depths were mounted. Channel migration was monitored using a DGPS. Migration of the channel only takes place where the channel crosses the sand flat and is very dependent on flow velocities. Bedforms showed a highly three dimensional pattern with lengths in the order of meters and heights in the order of decimetres. No migration of bedforms took place for flow velocities below 0.6 m/s. Inflow takes place in two pulses, while outflow occurs in one single pulse. The higher the tidal amplitude and the setup, the higher the flow velocities in the channel. The system as a whole is ebb dominated. Only during storm, water flows in over the large sand flats on each side of the channel, but flows out via the channel. No waves enter the inlet, except for infragravity waves under storm conditions. Quantifying bedload sediment transport with dune tracking techniques was not possible. The OBS and ADV measurements of suspended sediment concentration could only be used to deduce a general pattern in transport rates, but could not be quantified. The suspended sediment concentration is a result of local flow velocities. The concentration profiles from the ADV and OBS showed very good mixing of suspended sediment and show that in the Slufter a sand/mud mixture is in suspension. For bedload as well as suspended load, calculations showed almost no transport under calm weather conditions, an export of several cubic meters per fifty hours for more energetic weather conditions and an export of several tens of cubic meters under storm conditions. For the total transport, bedload as well as suspended load are important contributors. The amount and magnitude of storms is very important to the total net export through the Slufter inlet channel on the long term. For the Slufter system as a whole, import of sediment takes place during storm over the beach flat and mud is captured in the backbasin. These processes reduce the export of sediment for the system as a whole and thereby bring the system closer to equilibrium.