VARIATIONS IN RHEOLOGICAL PROPERTIES OF MUDS IN THE GIRONDE ESTUARY

Pascal Galichon, Alain Feral, Jerome Granboulan, Jacques Viguier

Abstract


In numerous navigation channels, the bed consists of muds. The navigability threshold adopted by many ports is currently that which corresponds to a specific gravity of 1.2. This virtual standard does not fully take into account the rheological characteristics of the muds, which may differ from one site to another. Investigations were carried out to determine the rheological properties of the Gironde estuary muds. Analyses were carried out in the laboratory on samples taken from different sites and on different dates and in situ, using the SR10 probe developed by SOGREAH and ultrasonic sedimentometric probe developed by the Bordeaux Port Authority. The results demonstrated the occurrence of major spatial and temporal variations. The two principal phenomena revealed by the research were that with the same dry sediment content: . muds were less rigid at the front of the maximum turbidity zone than at the back, by a factor of about 1.6 to 2.5, . the greater the annual flood, the lower the rigidity. A proper understanding of the spatial and temporal variations of rigidity is therefore essential to determine and adjust the navigability threshold.

Keywords


estuary; Gironde estuary; mud; mud properties

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