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Beach fetch distance and aeolian sediment transport



An experiment was conducted to examine the influence of fetch distance on aeolian sediment transport on a natural sand beach at Benone Strand, County Londonderry, Northern Ireland. The site consisted of a wide dissipative beach, approximately 150 m wide at low tide and 80 m wide during high tide. Surface moisture levels (and hence dry fetch distance) were dictated by both local groundwater, from a stream outlet across the beach, as well as local tidal levels. An abundant dry sediment supply was available during the experiment. High-resolution (1 Hz) measurements were made of wind speed and direction along with sediment flux. Wind velocity ranged from 2·1 to 8·1 m s–1 during the study. Second-order polynomial sand transport equations were derived from the wind speed and trap results with r2 values of better than 0·93 for all data. When the data were sorted into velocity bins of 1 m s–1, there was no discernible relationship between fetch distance and sand transport, with a measured fetch distance range of 10–58 m available during the experiment. Results show that fetch distance is unimportant when an adequate sand supply is available. However, it is suggested that fetch may restrict the development of steady-state transport under sediment-limited conditions. Sediment availability is thus identified as a key variable in aeolian transport studies on natural beaches.