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Figure 1. Concrete block structure housing the seawater recirculation system and laboratory at the Explor- 

 atory Fishing and Gear Research Base's dock site on the Pascagoula River. One of the elevated filter boxes 

 can be seen at the end of the building. The saltwater well is located beneath the filter box. 



designed to function in hydrostatic pressure 

 balance with the pool, and water flowed from 

 the pool into the sump whenever a hydrostatic 

 pressure imbalance was created by pumping 

 water out of the sump. 



A gravity-flow water delivery system was 

 selected for use in the recirculation system. 

 A head of hydrostatic pressure with sufficient 

 water volume is essential to provide a con- 

 tinuous water flow for an eff"ective gravity flow 

 system. This condition was met by using ele- 

 vated filter boxes which provided hydrostatic 

 pressure and water volume with sufficient fall 

 to ensure an acceptable gravity flow delivery. 

 Filtration of the water, immediately preceding 

 its return to the experimental tanks, was also 

 considered advantageous. 



Before the construction of the recirculation 

 system, clean water from the Gulf of Mexico, 

 for use in experimental tanks, was transported 

 to the laboratory by the research vessel George 

 M. Bowers. The complexity and cost of this 

 operation prevented its continued use. Con- 

 sequently, two alternate water sources, a salt- 

 water well and a high-salinity wedge in the 

 Pascagoula River, were used to supply the re- 

 circulation system. 



Consultation with the U.S. Geological Sur- 

 vey led to the drilling of a well adjacent to the 

 laboratory, and salt water was reached at a 

 depth of about 90 ft. A polyvinyl chloride 

 (PVC) casing and strainer were set in the drill 

 hole, and a 2-hp stainless-steel impeller pump 

 was used to raise the water. 



