4th International Conference of Palaeogeography

172 / 2019-06-06 16:13:14

Simulation experiment on coarse particle distribution and its influencing factors in braided river delta

Flume tank experiment; Coarse particle distribution; Braided river delta; Influencing factors;Sand body morphology

Coarse particles are the particles that represent tractive and rolled transportation, which are not easily re-transported after deposition under the impact of inertia and gravity after water flow velocity exceeds the starting flow rate of particles.
In simulation experiment, we discover that during the development of delta, the distribution of coarse particles affects the depositional process of delta and sand body morphology.
In river delta, coarse particles are mainly distributed in the following three locations: plain facies channel, front and lateral margin of lobe and the underwater curved ripple.
The coarse particles in river channel are affected by hydrodynamic conditions and particle properties and are mainly developed in Scour pits, river distributary beaches, river channel flank and floodplain surface. The accumulation of coarse particles will accelerate the erosion of river channel and the development of gullies, thereby affecting the diversion and migration of river.
During flooding period, large amounts of coarse particles are transported through sand body surface at the front and lateral margin of lobes. However, they are successively unloaded due to the uplift force of lake water at estuary and reduced flow rate.
Curved ripple is a type of ripple with curved ridge. It forms on sand body surface in a sedimentary environment where hydrodynamic force is gradually weakened. Small amounts of coarse particles at the front and lateral margin of lobes are stagnant at the trough of curved ripple affected by their own gravity and wave action when they are advanced to lake.
The main factors affecting the distribution of the delta coarse particles are the hydrodynamic conditions of river, the structure of debris particles, topographical conditions and the wave action near lakeshore line.