Sedimentation in the shear front off the Yellow River mouth

Based upon in-situ measurements and Landsat scanning images, spatial-temporal changes in the shear front and associated sedimentation in the subaqueous delta slope of the Yellow River have been studied, The results show that the shear front is an important dynamic factor in controlling rapid accretion at the Yellow River mouth. Suspended sediment converges and is deposited rapidly along the shear front zone; this is because a low-velocity zone is formed between two inverse flow bodies. Some small eddies occur in the shear front zone, shown on (method of concentration-temperature ratio) mapping; this is conducive to rapid convergence and accumulation of the suspended sediment in the shear front. At the same time, some hyperpycnal plumes and gravity-driven underflow may be formed; these move away from the shear front zone, due to the high sediment concentrations there. The shear front is formed firstly at the prodelta area; it then moves to the river mouth, in response to the flood or ebb tidal controls and deep sea influences, It moves along the subaqueous delta slope for 1/2-1/3 or me tidal cycle, during the over flood season. The shear front zone of low velocity forms a wall of water that prevents dispersal of the river outflow. The temperature image from TM6 shows that a river-sea interaction zone, a transition between the river and sea water temperatures, occurs around the mouth. The shear front is formed within this zone. A four-stage dynamic process, related to the shear front during the tidal cycle, is discussed, The results show that the shear front occurs twice during a tidal cycle. (C) 2001 Elsevier Science Ltd. All rights reserved.