Open AccessDYNAMICS OF SILT IN ESTUARY, RESIDUAL CURRENT OR FLOCCULATION WHICH PREVAILS?
Author(s) -
J.P. Lepetit,
M. Davesne
Publication year - 1980
Publication title -
proceedings of conference on coastal engineering/proceedings of ... conference on coastal engineering
Language(s) - English
Resource type - Journals
eISSN - 2156-1028
pISSN - 0589-087X
DOI - 10.9753/icce.v17.169
Subject(s) - turbidity , estuary , silt , flocculation , settling , salinity , hydrology (agriculture) , sediment , turbidite , saltwater intrusion , river mouth , environmental science , geology , salt marsh , soil science , geomorphology , oceanography , geotechnical engineering , groundwater , environmental engineering , aquifer
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.