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9. UPRIVER SALTWATER PENETRATION 



9 . 1 INTRODUCTION 



An estuary by definition is a semi-enclosed water body in which 

 seawater and fresh water from river mix under tidal action. Seawater is 

 thus diluted measurably (Cameron and Pritchard, 1963), and, in some cases, 

 penetrates in the form of a saline wedge upriver. In other cases the 

 waters are vertically well mixed, and salt water penetration occurs without 

 the presence of a distinct wedge. Water bodies which do not receive fresh 

 water tend to be highly saline, with salt concentration equal to that in 

 the sea. In some cases, e.g., in parts of Florida Bay, in southern 

 Florida, excessive evaporation during the hot and dry season renders the 

 waters super-saline, with salinity exceeding that in the sea (Atlantic 

 Ocean) . 



The three main parameters which control the degree of salt penetration 

 are the river runoff velocity, water depth and tidal range in the sea. 

 Increasing the tidal range or the depth, or decreasing the runoff will 

 increase penetration. In urbanized areas, withdrawal of fresh water and 

 dredging of deeper channels for vessel navigation are important issues ; 

 hence the effect of reduced runoff as well as the effect of increased depth 

 on salinity intrusion have been investigated by scientists and engineers. 

 The effect of reduced runoff has, for example, been recently investigated 

 in the Myakka and other rivers near Florida's Gulf of Mexico coast.-'- A 

 serious problem of this nature occurred in the Delaware River Basin in the 

 1960s due to drought. During the worst period, the salt front advanced 

 53 km up the river and forced some industries near Philadelphia to seek 

 water from a municipal system that imported water from the Susquehanna 

 River Basin (Hull and Titus, 1986). 



The influence of increased depth is analogous to what would occur (and 

 has occurred) in the event of a sea level rise. The propagation of tide up 

 the estuary is affected in this case. On the other hand, enhanced fresh 



■'-Ernest Esteves, Mote Marine Laboratory, Sarasota, Florida, personal 

 communication. 



