STOCHASTIC APPROACH TO PREDICT SURVIVAL 643 



data on the heat-resistance times of organisms acclimated in natural 

 environments, however. These data are needed to predict survival of 

 animal populations during passage through a power plant and its 

 cooling-water system. 



Previous studies at the P. H. Robinson Generating Station, 

 Bacliff, Tex. (McCullough, 1971; French, 1973; Reimer and Strawn, 

 1973; Landry and Strav^ni, 1974), indicated that numerous entrained 

 and entrapped organisms were killed by heat in the discharge canal. 

 Cooling towers, which have been added since those studies, reduced 

 summer temperatures in the lower half of the discharge canal. This 

 should increase survival of entrained organisms, but they may die of 

 heat shock in the discharge canal between the plant and the cooling 

 towers. 



Our study was designed to estimate seasonal survival times of 

 crustaceans and fishes at test temperatures similar to those of the 

 discharge canal and to predict, at mean seasonal temperatures, 

 seasonal survival probabilities of aquatic animals entrained and 

 entrapped from intake water and exposed to heated effluent during 

 passage through the discharge canal. This type of data can be used in 

 assessing the effect of power-plant design on the mortality of 

 entrained organisms. 



MATERIALS AND METHODS 



Study Area 



The study location was the Houston Lighting & Power Com- 

 pany's P. H. Robinson Generating Station, on state highway 146, ~1 

 mile south of Bacliff, Tex. Two 450,000-KW generating units, one 

 565,000-KW unit, and one 750,000-KW unit are capable of 

 pumping cooling water through the condensers at a total rate of 

 265,056 m^/hr. The plant uses cooling water drawn, via a 3.7-km 

 intake canal, from Dickinson Bay, a subsystem of Galveston Bay. 

 The water is heated as it passes through the plant's condenser-tube 

 network and returns to Galveston Bay via a 3.2-km discharge canal. 

 Organisms reach the discharge canal by passing through the revolving 

 screens and/or by being impinged on the screens and sluiced into the 

 discharge canal. A drop structure at the edge of Galveston Bay 

 prevents water from entering the discharge canal downstream except 

 during storm tides. 



The cooling towers, which operate from June through Sep- 

 tember, are located on the discharge canal between the plant and 

 Galveston Bay. Cooled water from the towers, which is mixed with 



