Generation of an estuarine sediment plume by a tropical storm

Abstract

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−1. 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.