Generation of an estuarine sediment plume by a tropical storm

Abstract

[1] Tropical Storm Lee (2011) caused a record flood in the Susquehanna River which discharged about 6.7 million tons of suspended sediments into the Bay, an amount equal to the input of 6 average years. The flood-carried sediment produced a large sediment plume that covered one half of Chesapeake Bay with the maximum suspended sediment concentration exceeding 2500 mg L-. Three stages were identified in the development of the sediment plume, corresponding to three dominant forcing mechanisms, i.e., river flow, estuarine circulation, and sediment settling. Most of the flood-carried sediments were deposited in the Bay within 20 days. Sands were dumped in the Susquehanna Flats with a maximum thickness of 10 cm, while fine-grained sediments were dusted over a wide area in the upper Bay with a maximum thickness of 4 cm. Long-term simulation of the post-storm period showed that a majority of the flood sediments were redistributed to accumulate in the estuarine turbidity maximum region due to flood-ebb asymmetry in tidal suspension and advection by estuarine circulation and tidal flows while the rest were transported seaward and deposited in the mid-Bay. It is estimated that the flood delivered 9 months of particulate nitrogen and over 1 year of particulate phosphorus supplies to the estuary. This catastrophic event may change the geological history and exacerbate water-quality decline in the American largest estuary. © 2013 American Geophysical Union. All Rights Reserved.