36 Artificial Aquatic Habitats 



enters the Cumberland River in Clay County, Tennessee. The combined 

 minimum flow when water is operating the three turbines is 5900 cubic 

 feet per second. When the turbines are not in operation, there is a natural 

 cold-water discharge of 19 cubic feet per second. Discharge schedules 

 vary from year to year; shutdown periods of several days are common in 

 the summer and fall, and levels of the tailwaters fluctuate within a 

 10-foot range. 



The water discharge below the Dale Hollow Dam is always clear 

 ( turbidity less than 5 ppm ) , and the water temperature of the discharge 

 ranges between 7.2° and 13.3°C (45° and 56°F). The minimum discharge 

 of 19 cfs has maintained a water temperature cool enough for trout in 

 the upper three miles of die tailwater during extended shutoff periods. 

 However, the best periods for trout fishing are on weekends when the 

 turbines are shut down and water levels are low. 



Dale Hollow Reservoir dam is 178 feet high, and the water depth at 

 elevation 651 ( spillway level ) is 151 feet. The annual water-level fluctua- 

 tion on this 30,000-acre lake is usually less than 25 feet. 



Excellent tailwater fishing for warm-water fish may occur where water 

 is released from a reservoir at surface or near surface levels ( Figure 2.7 ) . 

 Fish migrate upstream in the river formed from the overflow, and when 

 they reach the barrier of the dam, they tend to remain in the tailwater 

 pool. These tailwater fisheries never equal the fishing operations in the 

 reservoir above the dam,-^ but this seems to be so because the fishermen 

 are concentrated at the tailwater fisheries. 



Stroud and Jenkins -^ favor reservoir outlets located to release cold 

 water (often deficient in oxygen) from reservoir depths because there is 

 "a continuous discharge of oxygen-consuming decomposition materials 

 with the colder, deep waters." This prevents stagnation and makes 

 "maximum reservoir volume available for use by fish life." At the same 

 time, the warm upper water is retained to promote fish production. 



OTHER FACTORS AFFECTING THERMAL 

 STRATIFICATION 



Sometimes waters that enter lakes from feeder streams influence thermal 

 stratification because such waters seek their appropriate density (weight) 

 level. In south central Nebraska, a small reservoir built across Rock 

 Creek (a stream originating from a large spring) always contained 

 oxygen in the deeper water because the cold water entering from the 

 stream moved along the lake bottom carrying dissolved oxygen with it. 



In winter, water from tributary streams may be colder than the lakes 

 into which they flow, forcing lake water from deeper layers upward 



