Figure 3. Sediment grain size distribution at the study site. Results of grain size analysis carried out on sediment cores collected at the study-bend inner bank (a), outer bank (b), and channel thalweg (c). Different symbols of gray-shaded data points denote different coring depths, as shown by the inset in the lower-right corner. Detailed coring locations are shown in panel (d), together with a seaward-looking photo of the coring operation at the outer bank. Sediment coring was carried out on the last day of fieldwork to avoid damaging the channel morphology before flow measurements.
In order to investigate sediment properties at the study site, we collected sediment cores at the meander inner bank, outer bank, and channel thalweg using a custom hand corer (coring depth ranging between 60 and 80 cm). Grain-size analysis was carried out at 10 cm intervals from the core top using a Mastersizer 2000 laser granulometer with a measuring range of 0.02 ~ 2000 μm and a reproducibility error of < 3%. Grain-size parameters - including median size (\(d_{50}\)), standard deviation (\(\sigma_{d}\)), skewness (\(S_{d}\)), and kurtosis (\(K_{d}\)) - were calculated using the Moment Methods (Friedman, 1962). Consistently with sedimentary characteristics of the whole YTF system, sediments were found to be mostly cohesive, with clay volume content accounting for nearly 20% (Figure 3). The median grain size is always smaller than 62.5 μm (i.e., 4φ). No significant grain-size trends are observed from the core collected at the channel thalweg (Figure 3c), whereas fining upward trends are found both at the inner and outer bank (Figure 3a,b).
3 Methods