Assessing the influence of measured variabilities in the intertidal zone on predicted aeolian processes

Abstract

Additional thesis - The exchange and transport of sediment between intertidal zone and backshore are subject of ongoing research in order to assess the dynamic behaviour of sandy coastal systems. How the sediment moves in the coastal system is relevant knowledge for e.g. the Dutch coastal nourishment programme. It is a scientific challenge to describe and predict the transport of sediment. There is recent progress in describing the aeolian transport. De Vries et al (2014a) gives a new model approach for describing aeolian sediment transport in supply limited situations. The state of the art AeoLiS model covers the aeolian domain only and is not capable of describing the exchange between the shore face and the intertidal zone (de Vries, personal communication 2016). The aim of this additional graduation work is to assess the effect of variability in topography and grain size distribution on aeolian processes in the intertidal zone. It is hypothesised that there is a measurable daily variability of the topography and grain size distribution along the cross shore profile and that these factors have a significant effect on aeolian transport. Detailed measurements of the intertidal zone are needed to describe the topographic change of the intertidal zone and the variability in grain size distribution. From 11 till 15 October 2016 fieldwork was done at the intertidal zone near Kijkduin. With use of a laser scanner the daily topographical changes were monitored. Sediment samples were taken along the beach profile to assess the variability in grain size distribution. The gathered laser scan data was processed and a variability in topography was measured. The sediment samples were sieved in the lab to find the mean grain size, d50 per sample. A variability in d50 was measured along the profile. The influence of the variability in topography and grain size distribution on the aeolian sediment transport on a daily scale, is assessed using the AeoLiS model. The results of the simulations show that the measured variability in topography does not has a significant influence on the predicted aeolian transport. The influence of the variability in grain size distribution is illustrated with 3 sediment samples (with increasing d50 values). The sample with the smallest d50 gave surprising low results for the predicted aeolian transport. It appeared that this sample had a significantly higher fraction of coarse sediment (small pebbles/shell fractions) compared to the other samples. This was considered an outlier. After removing the outlier from the sample, the aeolian transport increased. Now, the results show that the predicted aeolian transport decreases with increasing grain sizes. The removing of the outlier shows the potential of armouring; a small fraction of coarser material in the bed can have a significant effect on the aeolian transport.