Field measurement of seasonal wind-blown sand flux using high-frequency sampling instrumentation

In order to investigate seasonal characteristics of instantaneous wind-blown sand transport in the field, field measurements using high-frequency sampling instrumentation were conducted in 2005 on a natural, open-ocean beach system in Japan. Datasets included 1-Hz blown-sand impact counts and three-dimensional wind conditions as well as hourly precipitation. During the measurement period, provability of detecting invalid impact count was only 1.6% and valid data shows a reasonable positive relationship between 10-min mean wind velocity and impact counts. The mean sand flux calculated from the impact count was greater when the mean wind angle was in the longshore direction (in winter); but decreased when the angle was in the seaward direction (in late summer and winter) compared to the longshore direction, and then decreased when the angle was in the landward direction (in spring and autumn) compared to the seaward direction. It decreased significantly during the rainfall phases. Large amount of sand was transported during typhoons. The sand mass flux calculated by an existing flux equation derived from wind tunnel experiments slightly underestimates the maximum measured flux for each wind velocity in the field, but approximately correspond with the maximum flux. This study demonstrates the usefulness of the high-frequency blown-sand flux sensor to measure the wind blown-sand flux for long-term period over nine months and indicated a number of seasonal characteristics of blown-sand flux especially during stormy events.