Elisa Reim Graduation Date: 29 November 2013 Graduation committee: University of Twente Dr. Ir. Jan S. Ribberink Dr. Kathelijne M. Wijnberg | Annual aeolian sediment transport from the intertidal beach This report presents a case study analysis of the quantification of sediment that is annually transported from the intertidal beach to the upper beach by wind at Egmond Beach in one particular year (2009). Semi-hourly collected ARGUS (digital monitoring system) video images from Egmond Beach, The Netherlands, of the year 2009 were used to identify the occurrence of aeolian sediment transport. Hourly averaged wind speed and wind direction data from IJmuiden and precipitation data from Wijk aan Zee were used to get insight into the effect of those factors on aeolian sediment transport occurrences. The sediment transport equation of Kawamura (1951) was used to calculate the amount of sediment that could theoretically be transported from the intertidal beach towards the upper beach and dunes during conditions in which actual aeolian sediment transport was observed. Moisture content was accounted for using the equation of Dong et al. (2002) and the effect of fetch limitation was accounted for by using the equation of Delgado-Fernandez (2010). It appeared that the hourly averaged wind speed data available from the long-term wind monitoring at IJmuiden was not an appropriate input value to calculate annual onshore aeolian sediment transport, as it lead to an underestimation of observed transport occurrences. A new ‘representative wind speed’ was developed to account for gustiness of the wind throughout the hour. The translation to a representative wind speed value was developed based on an analysis of high resolution time series for wind speeds from wind stations near Salt Lake City, United States of America. The most aeolian sediment transport occurrences were observed while wind was blowing alongshore or nearly alongshore the beach, which in the case of Egmond Beach means wind directions from South-West. Below an hourly averaged wind speed of 6 ms-1 almost no aeolian sediment transport occurrences have been identified. For 2009, the calculated annual onshore aeolian sediment transport was 9.4 m3m-1y-1, which is almost the same amount as found by Arens (2010), who calculated an average annual dune volume change for the region of 10 m3m-1y-1. Only in 5% of the aeolian sediment transport occurrences, the actual fetch distance was smaller than the theoretical critical fetch. The effect of the alongshore varying fetch distances on annual onshore aeolian sediment transport was calculated as 0.88 m3m-1y-1. This is 8% of the total annual onshore aeolian sediment transport. It can be concluded that the small amount of cases, for which the actual fetch distance is smaller than the critical fetch distance, can result in a non-negligible difference in annual onshore aeolian sediment transport. Overall, in this study a method has been developed to calculate representative theoretical annual onshore aeolian sediment transport.
. Figure 1: The analysed hours per wind speed |
