171 / 2019-06-06 16:06:45

Simulation experiment on the control of waves on delta front sand bodies

Flume tank experiment; Waves; Shallow water delta; Sedimentary process; Delta front

Experiment results reveal that the impact of waves on delta is dominated by destruction with the development of delta, making the longitudinal development ability of delta weakened. At the same time, waves obviously control the development and distribution of delta front sand bodies.
According to the development of distributary channel and the differences in wave actions, delta front is divided into estuary area and abandoned river channel area.
The hydrodynamic conditions in estuary area are jointly controlled by upstream water and the waves near shoreline. Waves have destructive effect on river channel. The sediments in estuary are always under-saturated due to the destructive effect of waves, and the river channel is not easy to migrate. On the whole, the main river channels are well-developed, but tributaries are small in number and range. Existing river channel is not easy to migrate, and the frequency of re-routing is slowed down.
The hydrodynamic conditions of abandoned river channel area are jointly controlled by wave and the local coastal current derived by waves. Wave action takes dominance. The entire development process is wave-dominated deposition-destruction-transportation-redeposition. According to the position of wave action, the front sand bodies near lake plane is divided into overlying area, elutriation area and carrying area from top to bottom. The elutriation area is near lake shoreline. Waves break up in this area, making the generated rushing and back flow moving repeatedly, so sand body surfaces are continuously washed and eroded. The fine particles on sand body surface are transported and coarse particles are exposed. Overlying area is in the upper part of panning area. The eroded fine sediments carried by rushing waves are regularly stacked and deposited, forming stripe sand bodies along lake shoreline. Carrying area is in the lower part of panning area. A large amount of eroded sediments are carried and deposited by gravity, backflow and local rip current, forming a large area of  annular strip sand bodies in the front and lateral margin of lobes.
Because the impact of waves is different in different positions, front sand bodies are reformed, representing a geomorphology of steepening in local, gentle as a whole and extending to lake area, which is quite different from general delta. The strip sand bodies and annular sand bodies formed by wave action in delta front are preserved in a short time due to the continuous development of delta, but when dry season is prolonged or delta is absent, they will become the provenance of the beach bar in lake shoreline under the impact of wind, waves and coastal currents.