CHESAPEAKE BAY LOW FRESHWATER INFLOW STUDY 



Alfred E. Robinson, Jr. 



Chief, Chesapeake Bay Study Branch, Baltimore District 

 U.S. Army Corps of Engineers, Baltimore, Maryland 



ABSTRACT 



Chesapeake Bay is the largest 

 estuary on the Atlantic coast of the 

 United States and one of the more im- 

 portant estuaries in the world. It 

 is nearly 200 miles long and varies 

 in width from 3 miles to 30 miles. 

 Like all estuaries, it depends upon 

 the inflows of freshwater to maintain 

 its salinity regime. Salinity varia- 

 tions, spatial and temporal, consti- 

 tute the most significant physical 

 parameter influencing the circulation 

 dynamics of the estuary and the 

 types of aquatic species which reside 

 in it. The quantity of fresh water 

 flowing into the Chesapeake may be 

 substantially reduced in the future 

 due to a marked increase in the con- 

 sumptive use of water. The Corps of 

 Engineers Low Freshwater Inflow Study 

 was conceived as a result of the con- 

 cern over this increased consumptive 

 use. The objectives of this study 

 are to assess the environmental, eco- 

 nomic, and social consequences of 

 these reduced flows and if appropri- 

 ate, to formulate criteria for mini- 

 mum freshwater inflows. A major por- 

 tion of this work will be based on 

 the results of a series of tests con- 

 ducted on the Chesapeake Bay Model. 



INTRODUCTION 



The Chesapeake Bay is the larg- 

 est estuary on the Atlantic coast of 

 the United States and one of the more 

 important estuaries of the world. The 

 bay is about 200 miles long and 



varies in width from about 3 miles 

 near Annapolis to about 30 miles at 

 its widest point near the mouth of 

 the Potomac River. It has a free 

 connection with the waters of the 

 Atlantic Ocean at its southern ex- 

 treme and is connected near its 

 northern extremity to the Delaware 

 Bay through the Chesapeake and Dela- 

 ware Canal. The tidal shoreline of 

 the bay and its tributaries is about 

 7,000 miles long while the water sur- 

 face area is about 4,300 square 

 miles. The surface area of the bay 

 proper is about 2,200 square miles 

 and its mean depth is less than 28 

 feet. The entire system, including 

 the tributaries to the head of tide, 

 averages about 21 feet deep. There 

 are, however, deep holes which occur 

 as long narrow troughs. These troughs 

 are thought to be the remnants of the 

 ancient Susquehanna River Valley 

 which have not been filled by post- 

 Pleistocene sediments. The deepest 

 of these holes (175 feet) is locat- 

 ed near Kent Island where the Chesa- 

 peake is at its narrowest. Figure 1 

 is a map of the Chesapeake Bay Area. 



The Chesapeake Bay receives wa- 

 ter from a basin over 64,000 square 

 miles in area. There are more than 

 50 tributary rivers with widely vary- 

 ing geochemical and hydrologic char- 

 acteristics contributing fresh water 

 to it. The largest river on the East 

 Coast of the United States, the Sus- 

 quehanna, drains 42 percent of the 

 basin. The Potomac River drains 22 

 percent, while the Rappahannock- 

 York-James system drains about 24 

 percent. 



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