^fitfioductici/i 



PURPOSE 



The objectives of this segment of the study are: (1) to inventory the fish 

 populations of the Tongue River Reservoir so that changes associated with coal 

 development can be detected and, if necessary, mitigative measures taken; (2) to 

 determine angler use and harvest of major sport fish in the Tongue River Reser- 

 voir; and (3) to evaluate possible impacts associated with large-scale withdraw- 

 al projects. 



STUDY AREA 



Flow of the Tongue River in Montana is controlled by the Tongue River Dam, 

 behind which lies the Tongue River Reservoir. The earthfill dam, completed in 

 1940, impounds over 84.9 hm-^ (69,000 af) of water with a surface area of 1,416 

 ha (3,500 acres). Firm annual yield is 49.2 hm^ (40,000 af). Sheridan, Wyoming, 

 the nearest city, is located approximately 32 km (20 mi) south of the reservoir. 

 The dam is 13 km (8 mi) north of the Montana-Wyoming state line (see figure 1 on 

 page 3 ), impounding water from a drainage area of 4403 km^ (1,700 mi^). 



Decker Coal Company, a subsidiary of Peter Kiewit Sons' Co., began mining 

 coal near the Tongue River Reservoir in 1973. Over 3 million tons of coal were 

 removed by Decker in 1973; the 1976 level of production was 10.3 million tons. 

 Currently, mining operations are confined to the west side of the reservoir, 

 but Decker is expanding (subject to permit approval) to the north of current 

 operations and to the east side of the reservoir (figure 29). When these ex- 

 tensions are in operation, the Decker operation will be the largest producing 

 strip mine in the world, with an estimated annual production of 14.5 million 

 tons by 1980. 



The Tongue River and Tongue River Reservoir may be increasingly important 

 in light of proposed coal development. While most coal mined in Montana now 

 leaves the state, additional coal conversion plants (for example, for steam- 

 fired generation, gasification, and liquefaction) close to the coal source have 

 been proposed. Such energy complexes require great amounts of water, and the 

 Tongue is considered an important source of industrial water. Montana Power 

 Company took an annual option on 5.15 hm^ (4,175 af) of Tongue River Reservoir 

 water in 1972. A generation plant in Wyoming which would utilize Tongue River 

 water has been suggested. 



However, water for industrial development in the Tongue River Basin would 

 not be firmly available without additional storage. In a 1969 study, Bechtel 

 Corporation considered a new Tongue River dam site about 10 miles downstream 

 from the existing site. Stage 1 of the proposed reservoir, flooding land in 

 Montana only, would have an active storage of 395 hm^ (320,000 af) and firm 

 annual yield of 120 hm-^ (100,000 af). Stage 2 of the proposed reservoir, be- 



79 



