646 CHUNG AND STRAWN 



where t = time exposed 



P2(t) = probability of survival in the discharge canal efferent to the 

 cooling towers 

 Xj = death rate in the discharge canal afferent to the cooling 



towers 

 X2 = death rate in the discharge canal efferent to the cooling 

 towers 



These two effects were assumed to be independent. On the basis 

 of water flow, we assumed that animals took 30 min to reach the 

 cooling towers and estimated that as much as 150 min could be 

 required to travel from the cooling towers to the area of reduced 

 temperature in Galveston Bay. 



In these three analyses the year was divided into three seasons, 

 on the basis of water temperature, hot (June— September), cool (May 

 and October), and cold (November— April). Each season was ana- 

 lyzed separately. Death rates in the discharge canal afferent and 

 efferent to the cooling towers were estimated from laboratory 

 experiments using experimental temperatures similar to seasonal 

 averages in the discharge canal. Average discharge temperatures were 

 27° C in the cold season, 32°C in the cool season, and, during the hot 

 season, 40°C afferent and 35°C efferent to the cooling towers. 



RESULTS AIMD DISCUSSION 



Temperature and Salinity 



Temperature ranged from 7.2 to 30.5°C in the intake canal, from 

 19.4 to 41.6° C in the discharge canal above cooling towers, and from 

 14.4 to 37.8° C below the towers. Average monthly temperatures in 

 the intake canal and in the discharge canal afferent and efferent to 

 the cooling towers ranged from 26 to 30, 36 to 40, and 33 to 35°C, 

 respectively, in the hot season; 23 to 26, 32 to 35, and 31 to 34°C, 

 respectively, in the cool season; and 13 to 19, 26 to 30, and 23 to 

 28° C, respectively, in the cold season (Fig. 1). From October to May, 

 effluent temperatures were under 35°C and the cooling towers were 

 not operated. The difference between average water temperatures in 

 the intake canal and in the upper part of the discharge canal was 

 about 10° C during all seasons. Average water-temperature reductions 

 from the upper part of the discharge canal to below the cooling 

 towers were approximately 4.5 and 5.5°C in the hot seasons of 1974 

 and 1975, respectively. The difference between average water 

 temperatures in the two summers was caused by operation of an 

 additional cooling tower in 1975. 



