Application of geostatistical grain size trend analysis in the Luanhe River Subaqueous Delta

With the grain size data of 85 surface sediment samples collected from the Luanhe River Subaqueous Delta (LRSD), we studied the sediment transportation trend using the geostatistical grain size trend analysis method (GSTA) in this paper. It is revealed that the semi-variance value of mean grain size in a regular grid increases with distance until the distance reaches 0.09 decimal degree, while the irregular data shows no such a correlation with distance. Thus, the decimal degree of 0.09 is chosen as the character distance for grain size trend analysis. It is further revealed that the direction of the semi-variance is 55°, which is parallel to the tidal current, suggesting that the character distance is tide related. Geostatistical GSTA result further indicates that the net sediment transport trend direction in the south area, where the water depth is less than 12 m, is in southwest, whereas that in the north area, where the depth is less than 12 m, is in west and southwest directions. In the area with water depth between 12 and 15 m, the net sediment transport trend is in southwestern direction, roughly parallel to the coast line. In the area under water depth more than 15 m, the net sediment transport trend is northwest in direction in the southern part, but southeast direction in the northern part. The grain size net sediment transport trends mentioned above are similar to the field measured tidal current, residual current, and sediment transport directions suggesting a tide predominated sediment transportation. However, relict sediments, wave, river and bedform are more complex, which may give influences the grain size net sediment transport trend. The research results of the net sediment transport trend in LRSD may reveal the influence of tidal current. However, for an explanation to relict sediments, further researches are required.