536 MOSS, BOONYARATPALIN, AND SHELTON 



maximum advertised transmitting time of 8 weeks, a range of 2 to 5 

 km, and different pulse rates to permit identification of individual 

 fish on a common carrier frequency of 74 kHz. The transmitter 

 weighed 49 g in air and 30 g in water. 



Bayshore Systems T-3T series tags incorporate a thermistor in 

 which the pulse rate varies with the water temperature. An analog 

 temperature decoder was used in conjunction v^th the receiver to 

 display the pulse rate, which was converted to temperature on a 

 calibration curve. The T-3T transmitter had a maximum advertised 

 transmission time of 6 to 8 weeks and a transmission range of about 

 825 m. It weighed 24 g in air and 15 g in water. Different 

 transmitting frequencies were used to identify individuals. 



STUDY AREA 



The Gaston Steam Plant, operated by Alabama Power Company 

 and located on the Coosa River about 3 km northeast of Wilsonville, 

 Ala., is one of the largest steam plants in Alabama, with a total 

 capacity of 1880 MW from five operational units. One unit is 

 equipped with cooling towers and, therefore, does not discharge 

 heated water. Cooling water is drawn from Yellowleaf Creek and 

 discharged into the Coosa River. 



Our study was limited to a 10.6-km section of the Coosa River 

 £ind a 4.5-km portion of Yellowleaf Creek, a large tributary adjacent 

 to the steam plant. The Coosa River in this region averages about 

 270 m in width and 6 m in depth. The maximum channel depth 

 varies from 1.5 to 30 m. The plant is approximately 27.2 km 

 downstream from Logan Martin Dam and 36.8 km upriver from Lay 

 Dam. The mainstream currents were generally moderate (33 to 36 

 m/min) but fluctuated according to the relative discharges from 

 Logan Martin and Lay reservoirs. Water level fluctuations were small 

 because discharge from the downstream reservoir was coordinated 

 with release from the upstream one. 



Water released from Logan Martin Dam altered the temperature 

 pattern that had been established around the plant during the 

 preceding period of no hydroelectric discharge. Temperatures in the 

 area affected by the discharge from the plant frequently exceeded 

 those in the upstream river channel by as much as 10°C, but the 

 increased flow of cooler water from upstream decreased the water 

 temperature as much as 6 to 10°C. The heated effluent dissipated 

 rapidly during cool months but noticeably affected ambient river 

 temperatures during the warmer months. The thermal effluent was 

 discharged at a depth of about 6 to 9 m but rose rapidly to the 



