145 



9 . 4 EXAMPLES 



It suffices to examine the effects of channel deepening and runoff on 

 salinity intrusion as paradigms (qualitative in the case of runoff) for 

 what would occur in the case of a sea level rise. 



A major salinity intrusion problem developed in the Maracaibo estuary, 

 Venezuela, in the sixties (Partheniades , 1966). The problem was traced to 

 the construction, during the previous years, of a deep, 60 km long, 

 navigation channel connecting Lake Maracaibo to the Gulf of Venezuela. A 

 representative salinity (chlorinity) record within the lake during the 

 1937-63 period is shown in Fig. 9.3. A significant fluctuation of salinity 

 first occurred during the 1947-52 period. This rise in salinity, from 

 typical values of 500-700 ppm during the previous and the subsequent years, 

 to a peak of about 1,400 ppm, is believed to have been due to the 

 occurrence of a dry period with low runoff. However, following the 

 completion of the deeper (from 6 m to 11 m) channel in 1956, the salinity 

 increased relatively rapidly and almost continuously to a peak of 1,500 ppm 

 in 1959. At this time, to accommodate yet larger oil tankers, the channel 

 was further deepened to 13.5 m. This caused a further increase in salinity 

 and, in 1962-63, when the deepening project was completed, the salinity 

 rose to 2,200 ppm. A physical model of the estuary was subsequently 

 constructed to examine the problem in further detail (Brezina, 1975). The 

 ultimate outcome of the channel deepening projects was to turn Lake 

 Maracaibo from a relatively fresh water lake into a brackish water lagoon, 

 with a complete change in life forms-^. 



The effect of dredging is commonly evaluated for environmental impact 

 statements. Such a study was carried out as prerequisite to the 

 construction of the Trident submarine base at King's Bay, Georgia. The 

 ocean entrance to this bay is through St. Mary's Entrance, Florida. 

 Fig. 9.4 shows the application of Eq. 9.1 for predicting the high and low 

 water (tidal range 2.2 m) salinity profiles in this prototype case, prior 

 to dredging (Parchure, 1982). Although agreement between theoretical 

 curves and measured data is obviously very rough, the theory, although 



■^Jindrich Brezina, University of Zulia, Maracaibo, Venezuela, personal 

 communication. 



