Experiments were conducted on Magilligan Strand, Northern Ireland, to assess the influence of theFetch Effect on aeolian sediment transport. During each experiment surface sediments wereuniformly dry and unhindered by vegetation or debris. The leading edge of erodible material waswell defined, with the limit of wave up-rush demarcating the wet-dry boundary; the work wasconducted during low tides. A number of electronic and integrating traps were utilised, with twoultrasonic anemometers used to measure wind direction and velocity at 1 Hz. The combination of1 degree direction data and trap locations resulted in a range of fetch distances, from 2 – 26 m. Data integrated over 15-minute intervals (corresponding to the integrating trap data) revealed a distinct trend for all the experiments. An initial rapid increase in the transport rate occurred over a short distance (4–9 m). This maximum transport rate was maintained for a further 5-6 m before a steady decay in the flux followed, as fetch distance increased. A measured reduction in wind speed (6-8%) across the beach suggests a negative feedback mechanism may be responsible for the diminishing transport rate: the saltating grains induce energy dissipation, thus reducing the capability of the wind to maintain transport. For one experiment, the presence of compact sediment patches may also have contributed to the reduction of the transport rate. The decay trend calls into question the utility of the fetch effect as an important parameter in aeolian studies that seek to understand sediment budgets of the foredune-beach zone.
- Aeolian fetch distance beach sand