Effects of Tropical Storm Agnes on the Suspended Solids of the Northern Chesapeake Bay

Abstract

In the upper reaches of the northern Chesapeake Bay the~ ~ two distinctive distributions of suspended sediment and associated patterns of sediment transport. During the spring f~shet, the Susquehanna River overpoweps the characteristic net non-tidal estuarine circulation in the upper 20-30 km of the estuary and the net flow and sediment transport ~ seG1J)aro at all depths. Generally the bulk-probably 70 to 75 percent-of each year's supply of new fluvial sediment is introt1u.ced during the spring freshet ~hen both riverflow and concentration of suspended sediment are normally highest. The marked dec~ase seG1J)ard of the concentration of suspended solidS in the upper bay ~veals the close link, during the freshet, between the suspended sediment population and the principal "ultimate" source of fluvial sediment-the Susque-hanna river. With subsiding river flow, the net non-tidal estuarine circulation is re-established in the upper ~aches of the bay and a turbidity maximum is for:med near the head of the estuary. The high concentrations of suspended solidS, g~ater than those either farther upstream in the source river or farther seG1J)aro in the estuary, a~ produced and maintained primarily by the periodic ~suspension of bottom sediment by tidal scour and by the sediment t~ c~ated in the upper ~aches of the estuarine circulation ~gime. The passage of tropical storm Agnes in June 1972, resulted in ~cord flooding throughout the drainage basin of the northern Chesapeake Bay. On June 24, the day the Susquehanna crested at its mouth, the instantaneous peak flow exceeded 32,000 m 3 /sec. The daily average discharge of 27,750 m 3 /sec.