Surface sediment distribution pattern of the Xinqiao Channel of Changjiang Estuary and its controlling factors

Flood-dominated channel is an important geomorphic unit in estuaries. Its dynamic sedimentation process is directly related to the dynamics of erosion-deposition system of the channel. However, due to the runoff-tide interaction and intensive human activities, the dynamics of sedimentation process for most of estuarine flood channels in the world is rapidly changing, led to channel shrinkage. Based on the grain-size parameters of the surface sediments collected along the Xinqiao Channel, the largest flooding channel in the South Branch of Changjiang Estuary, the distribution pattern of the surface sediments in the Xinqiao Channel and its influencing factors are carefully studied in this paper with the method of empirical orthogonal function (EOF). The Xinqiao Channel can be divided into three depositional zones. The upstream of the channel is mainly composed of silty sand and clayey silty sand which are poor in sorting and the middle of the channel is characterized by well sorted sands, while in the downstream of the channel, the sediments are mainly composed of sand, silty sand, sandy silt and clayey silty sand, which are poorly sorted. From the viewpoint of sedimentary dynamics, the surface sediments in the Xinqiao Channel can be classified into three modes. The major mode is dominated by sandy silt and clayey silt prevailed in the upstream and part of the downstream, deposited under the control of the joint action of runoff and tide. The secondary mode is dominated by silty sand in the middle and part of the downstream, under the control of local fluvial regime. The third mode, characterized by sandy deposits, is formed by runoff in flooding seasons. In addition, the downward movement of the tail of Biandan Shoal has enhanced the runoff entering the Xinqiao Channel, that results in the coarsening of surface sediment. The construction of the Dongfengxisha Reservoir caused to the fining up of surface sediment at the tip of upper Xinqiao Channel.