runoff into the entire Bay, and 87 percent of that north of the mouth 

 of the Potomac. 



The Potomac River estuary drains 22 percent of the Bay drainage 

 basin and contributes about 18 percent of the total freshwater inflow 

 into the Bay. The annual contributions by the other western rivers are: 

 James - 16 percent; Rappahannock - 4 percent; York - 2 percent; and 

 others - 4 percent. The eastern rivers (Choptank, Nanticoke and Wicomico) 

 contribute only 7 percent of the total runoff. 



The surface salt gradient over the 165 mile length caused by this 

 silution ranges from about 30 parts per hundred at the entrance, to 15 

 near the mouth of the Potomac River about 70 miles up the Bay, to a 

 freshwater condition in the inner reaches where the Susquehanna River 

 enters. Spring floods and summer-fall dry (relatively) periods contribute 

 to seasonal variations in salinity throughout the Bay! At equivalent 

 latitudes, higher surface salinities are found on the eastern side because 

 of the lower freshwater inflow there. Within the individual tidal river 

 estuaries a salt gradient is also found. Generally, for those systems 

 from the Patuxent River southwards, the surface salinity is 15.5 parts 

 per hundred at the mouth which decreases upstream, the characteristic of 

 the gradient depending on discharge volume and related features. 



LAND USE 



In general terms the immediate Chesapeake Bay watershed, including 

 the tidewater counties of Maryland, Virginia, and Delaware, covers an 



