Nature of the Turbidity Maximum in the Tamar Estuary, U.K.

Two synoptic, spring-tide, multi-station experiments in the 31 km-long Tamar Estuary were analysed for suspended particulate matter (SPM) concentrations and transport. SPM concentrations were very low in the seaward reaches and were largely associated with the flushing of fresh water from the estuary. Depth-averaged SPM concentrations in the upper 8•5 km of estuary were of the order of 103 higher than those near the mouth under similar, low-runoff, spring-tide, summer conditions. Local resuspension and advection of locally resuspended sediment from nearby bed-sources in the upper 8•5 km of estuary dominated the SPM loads during the flood. Highest SPM concentrations occurred during peak flood currents in the fresh water at 4•5 km from the head. At high-water, this location was in the vicinity of the freshwater-saltwater interface (FSI). During the ebb, SPM maxima occurred in fresh water throughout the upper 8•5 km of estuary. Near-bed measurements and longitudinal-transect data in the upper estuary showed that the FSI had an important influence on intratidal SPM variations.