Seasonal variation of sediment deposition in the Hudson River estuary

During and following the spring freshet, rapid rates of sediment deposition were observed in the Hudson River estuary. Side-scan sonar surveys and sed iment coring studies revealed a large amount of spatial variability in sedi mentation within the estuary and a distinct seasonal progression. During th e freshet, sediment was deposited in the seaward reaches of the estuary. In the two-month period after the freshet, this sediment was eroded and sedim entation occurred 10-30 km further landward at the estuarine turbidity maxi mum (ETM) zone, The thickness of the new freshet deposit was as great as 40 cm in the ETM, indicating intense trapping and rapid deposition. The locat ion of this depocenter corresponded to a frontal zone, where water column o bservations and modeling studies have indicated enhanced sediment trapping. The mass of the new deposits was estimated at 300 000 metric tons during b oth 1998 and 1999, with similar spatial distributions. In 1998 the estimate d fluvial input was 560 000 metric tons, significantly greater than the 120 000 metric tons estimated for 1999. Thus, the mass of the observed deposit s appear to be more influenced by the redistribution of sediment within the estuary due to seasonal variations in erosion-deposition conditions, rathe r than by the direct input of sediment from the watershed. (C) 2001 Elsevie r Science B.V. All rights reserved.