FIELD INVESTIGATION OF SIZE DISTRIBUTION OF SUSPENDED SEDIMENT USING LISST-100

To investigate size distributions of suspended sediments in the surf zone, a field measurement using LISST (Laser In-Situ Scatter and Transmissometer) was conducted at Hasaki, Japan. The time series of suspended sediment concentration (SSC) for a grain size in the sand range (63 to 500 m) had strong correlations with those for other sand grain sizes, and the strong correlations were also observed in the silt range (2.5 to 28 m). However, at zero time lag, the time series of SSC for sand grain sizes had little correlations with those for silt sizes. With considering time lag, the time series of SSC for sand sizes had weak correlations with those for silt sizes, but which time series lagged behind the others, sand particles or silt particles, was not clear. When the total SSC CLISST was larger than 0.2 g/l, the median sediment diameter d50 was scattered around 185 m. However, at CLISST < 0.2 g/l, d50 increased as CLISST increased. With the increase in d50 from 150 to 200 m, the sorting coefficient decreased from 2.4 to 1.2 and the skewness increased from 0.7 to 1.0.