关键词: 沉积物搬运, 粒度参数, 粒径趋势, 胶州湾

Abstract: Sediment characteristics are important for understanding of hydrodynamic processes and sedimentary environments. In the present study, 87 sediment samples were collected from Jiaozhou Bay and adjoining areas, Shandong Peninsula, China; 81 of the samples were analyzed using a Cilas 940L Laser Analyzer and by sieving (for particles with a diameter of <2 mm and >2 mm, respectively) to obtain grain size data. Three grain size parameters i.e. mean grain size ( μ ), sorting coefficient ( δ ) and skewness ( S k ) are then calculated by a moment method (McManus, 1988). The result shows that 9 types of sediment are present in Jiaozhou Bay and adjoining areas according to the sediment classification scheme proposed by Shepard (1954) and Blair McPherson (1999). The sediment distribution pattern is complex, indicating a multi source nature of sediment supply for the study area. Mean grain size and sorting coefficient for the sediment in Jiaozhou Bay is -0 4～7 5Φ and 1 2～4 3, respectively. The coarse (i.e. μ <0 65Φ) and well sorted (i.e. δ <2) sediment is located over the central and southwestern parts of the bay, where the sediment is negatively skewed, with a minimum S k value of -3 8. The sediment at the mouth of Jiaozhou Bay is the coarsest ( μ =-0 4Φ) and positively skewed ( S k =3 3). Good correlation between the distribution pattern of the grain size parameters in Jiaozhou Bay and the sediment types (and hydrodynamics processes) is present. The two dimensional models for grain size trend analysis proposed by Gao and Collins (1992) are adopted to identify sediment transport pathways in the study area. This method is on the basis of the assumption that in the direction of transport the sediment becomes either better sorted, finer in grain size and more negatively skewed, or better sorted, coarser in grain size and more positively skewed. Further, in order to use this model for the grain size trend analysis to deal with the situation that the sampling sites are not evenly distributed over the study area, the area is divided into 4 subareas. For each of the sub-areas, different characteristic spatial sampling intervals are adopted. Grain size trends are then obtained by using this model, with the “edge effect” being removed. The net sediment transport pathways in Jiaozhou Bay and adjoining areas thus derived show that sediment is transported towards the central sand bank within the bay and the seaward end of the deep channel at the mouth of the bay. Such patterns are highly consistent with those of current velocities, geomorphologic information and heavy mineral movement. Therefore, the grain size trend model is applicable for coastal areas with complicated sediment distribution patterns and irregular sediment sampling grids.

Key words: sediment transport, grain size parameters, grain size trends, Jiaozhou Bay