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Lynch, K.,Delgado-Fernandez, I.,Jackson, D. W. T.,Cooper, J. A. G.,Baas, A. C. W.,Beyers, J. H. M.
2013
Alongshore variation of aeolian sediment transport on a beach, under offshore winds
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Understanding the morphodynamics of beach-dune systems requires knowledge of the spatio-temporal variability of the sediment transport system. It is common in aeolian studies to employ a single transect instrument set up, oriented parallel to the wind direction. This experimental design assumes that there is no significant variation in sediment transport lateral to this direction. A limited number of recent studies into this lateral (or spanwise) variability have revealed substantial differences in transport rates over very short spanwise distances (<4 m). Research investigating scales of 10 s of metres is even more limited. This paper examines alongshore variability of aeolian sediment transport at this scale. Data were collected over eight hours during an offshore wind event. Thirteen Jackson traps were deployed, co-located with three-dimensional ultrasonic anemometers (UAs). The instruments were deployed in a grid covering an area of 55 m cross shore and 90 m alongshore. The data were analysed as 5 and 10 min totals, and were mapped for visual assessment of transport patterns. Alongshore variability was quantified using the coefficient of variation (CV). Results confirm identifiable spatio-temporal patterns in sediment transport. The CV results show alongshore variability ranging from 12% to 48%, with the lower beach traps showing much greater spatial variation. These values are comparable to earlier studies. The implications of recent research into secondary airflow patterns over dunes are discussed in light of the results presented.Understanding the morphodynamics of beach-dune systems requires knowledge of the spatio-temporal variability of the sediment transport system. It is common in aeolian studies to employ a single transect instrument set up, oriented parallel to the wind direction. This experimental design assumes that there is no significant variation in sediment transport lateral to this direction. A limited number of recent studies into this lateral (or spanwise) variability have revealed substantial differences in transport rates over very short spanwise distances (<4 m). Research investigating scales of 10 s of metres is even more limited. This paper examines alongshore variability of aeolian sediment transport at this scale. Data were collected over eight hours during an offshore wind event. Thirteen Jackson traps were deployed, co-located with three-dimensional ultrasonic anemometers (UAs). The instruments were deployed in a grid covering an area of 55 m cross shore and 90 m alongshore. The data were analysed as 5 and 10 min totals, and were mapped for visual assessment of transport patterns. Alongshore variability was quantified using the coefficient of variation (CV). Results confirm identifiable spatio-temporal patterns in sediment transport. The CV results show alongshore variability ranging from 12% to 48%, with the lower beach traps showing much greater spatial variation. These values are comparable to earlier studies. The implications of recent research into secondary airflow patterns over dunes are discussed in light of the results presented.
1875-96371875-9637
http://www.sciencedirect.com/science/article/pii/S1875963712000419http://www.sciencedirect.com/science/article/pii/S1875963712000419
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