ABSTRACT 



A relationship is derived from tine circulation pattern of a 

 piedmont-type estuary which expresses the time required 

 for a contaminated estuarine volume containing dissolved or 

 suspended matter to be replaced by tidal action and river 

 flow. The volume of such an estuary consists of an upper 

 layer of mixed water with a net seaward movement, overlying 

 a layer of sea water with a net landward movement. These 

 volumes are separated by a surface of no net horizontal 

 motion through which there is a net vertical movement of 

 sea water into the mixed layer. Hence, the lower layer is 

 renewed by tidal action alone while the mixed layer is re- 

 newed by tidal action and river runoff. 



Since the net seaward flow of mixed water is equal in volume 

 to the net landward flow of sea water plus the river flow, the 

 balance should be indicated by tidal current data. Thus, it 

 is possible to compute the flushing time without first com- 

 puting the river flow. 



In embayments and/or estuaries during a dry season, a rela- 



"~~ ■ ' ^ ' ' '"""' " "^e flushing time 



he tidal prism 

 ithe segments. 

 )ncentration of 

 1 the exchange 



