SECT. 3] 



ESTUARIES 



315 



reduce the degree of vertical stratification. Thus, though the average salinity 

 in the vertical within the harbor is very nearly the same as that found in the 

 adjacent Chesapeake Bay, the surface waters of the harbor are saltier than the 

 surface waters of the bay, while the bottom waters in the harbor are fresher 

 than water at similar depths in the bay. An example of the vertical distribution 

 of salinity in Baltimore Harbor and in the adjacent Chesapeake Bay is given in 

 Fig. 1. 



Salinity %c 



10-- 



20-- 



30-- 



40 J. 



10 



_1_ 



Fig. 1. Typical salinity vs. depth curves for (A) the Chesapeake Bay at the mouth of 

 Baltimore Harbor and (B) near the head of Baltimore Harbor. 



As a consequence, a horizontal density gradient exists between the waters 

 of the bay and those of the harbor, and this gradient varies markedly with 

 depth. In the surface layers an accelerative force is directed from the fresher 

 waters in the bay toward the denser, more saline, surface waters of the harbor, 

 and because of the constraints of the side boundaries, an inflow of the surface 

 layers along this pressure gradient into the harbor occurs. On the other hand, 

 the denser, more saline, deep waters of the bay also flow into the harbor since 

 the waters on the harbor bottom are less saline than the bay waters at the same 

 depth, just as sea-water flows into the estuary proper along the bottom. 

 Outflow from the harbor to the bay occurs at mid-depth. 



This three-layered flow pattern has the appearance of two simple estuarine 

 flow patterns, one on top of the other. In the upper pattern the Chesapeake 

 Bay appears as the source of fresh water and the harbor as the source of salt 

 water, or as the "ocean". In the lower half of the water column, the roles of 

 the harbor and the bay are reversed. Fig. 2 shows a typical longitudinal section 

 of the salinity distribution and flow pattern for this system. 



This three -layered type of flow pattern was first described by Pritchard and 

 Carpenter (1960) and Carpenter (1960). In the case of Baltimore Harbor it 



