DYNAMICS OF SILT IN ESTUARY, RESIDUAL CURRENT OR FLOCCULATION WHICH PREVAILS?

Proceedings of the International Conference on Coastal Engineering

J.P. Lepetit¹  M. Davesne¹ 

[1] Division Hydraulique Maritime. Laboratoire National d'Hydraulique. Electricite de France

关键词: estuary;    estuary dynamics;    residual current;    flocculation;    current;   

DOI  :  10.9753/icce.v17.%p

学科分类：建筑学

来源: Coastal Engineering Research Council

【 摘 要 】

The transport of fine suspended sediment in a partly-mixed estuary has been simulated on a physical model of a schematic estuary reproducing the main geometrical and hydrodynamical characteristics of the Gironde Estuary (France). The natural sediment consisting of silt and clay is simulated using a light and fine material, gilsonite, and the flocculation-'processes in salt water and under turbulence induced by tidal currents have been reproduced by adding in salt water a flocculating salt solution (sodium pyrophosphate). Then the formation of the turbidity maximum surveyed in the field and its upstream-downstream migration in response to varying river discharge have been successfully simulated and the results of different series of tests lead to the following conclusions : - flocculation processes - which are responsible of the variation of the settling velocity with salinity and turbulence-have to be reproduced to explain the formation of the turbidity maximum ; - after high river discharges the convergence of bottom residual currents (null point) due to the salinity intrusion creates a trap for suspended sediments supplied by the river flood which accumulate in the form of the turbidity maximum. Without salinity intrusion, a large amount of sediment would escape out of the estuary to the sea ; - during low river flows, a part of the suspended sediment migrates upstream but the amplitude of this migration is small compared with the displacement of the upstream limit of the salinity intrusion ; - the upstream migration of the turbidity maximum-is increased when a transverse bottom morphology (existence of a deeper navigation channel) is represented.

【 授权许可】

Unknown