WSP08430 - Laserfiche WebLink

Home Browse Search

001142 5 The environmental baseline condition was similar to the existing demand condition but included depletions which would result from certain projects not built at the time of the HYDROSS modeling effort. Included are all existing projects in the basin, all projects which have undergone Section 7 consultation, and all private water projects which are reasonably likely to be developed. The change from the existing condition to the environmental baseline condition involved adding these new depletions over the entire 1930-1982 period, Projects which have undergone Section 7 consultation include the Cheyenne Stage II water supply system and expansion of the Craig Power Generation Station (Craig 1Il). The Cheyenne Stage II project is located in the headwaters of the Little Snake River, Private water projects which are considered reasonably likely to occur include altering the use of four existing reservoirs in the basin. Included are Yamcolo Reservoir, Lake Catamount, Steamboat Lake and Elkhead Reservoir. These reservoirs have been managed primarily as recreational facilities and to serve agricultural demands, Future uses, however, could result in an additional depletion of 19,000 acre.feet on an annual basis. The environmental baseline conditions have been used for planning purposes by the USFWS in efforts to define flow recommendations for the T & E fishes. ' The final model scenario Baseline ~ Stagecoach Reservoir Proiect is essentially the same as the environmental baseline but includes depletions associated with Stagecoach Reservoir (12,800 af).. Comments on HYDROSS Modeling Our review of the HYDROSS application to the Yampa River Basin raised some questions regarding assumptions included in the environmental baseline case and identified some potential data entry problems in the data and network files. The apparent data problems are small in terms of average stream hydrology but did result in an inexaCt calibration of the network implementation and the HYDROSS results; when they were carried through to the network application an exact calibration was achieved. The questionable assumptions involve the magnitude of change in water demands. between the historical and environmental baseline case. No issue is taken with the historical case, which merely provides gaged flows as a starting point. The assumed reserVoir consumptive use includes 3,600 af of depletion attributable to Hayden and Craig (!W.W. Wheeler, 1989). Because Hayden and Craig depletions are counted elsewhere in the model, this appears to result in 3,600 af of excess depletion. The Hayden Unit 2 depletions of 4,700 af are counted from 1930 through 1966. However, Hayden 2 did not operate until 1976, Therefore, there appears to be 4,700 af of uncounted depletion from 1967 through 1975, :,1 The depletions attributed to thermal generation appear to be iarge relative to historical averages. In the environmental baseline, the Hayden plants are assumedto deplete 7,100 af and Craig units I,ll and 111 deplete 19,200 af. Over 1985 to 1989, Hayden actually depleted an average of 5,300 af, and in 1988 and 1989, the Craig units depleted an average 12,500 af (Davenport, Colo. Ute, personal communication). Even if opera'ted at 90% capacity, the Craig units should require only about 16,400 af of depletion. ;~ i * Losses associated with Stagecoach Reservoir (12,800 at) were also added in for the Baseline plus Stagecoach Reservoir Proiect scenario. Because Stagecoach is not operated with much regulariry these depletions might be interpreted as being large given current conditions. According to data on -~ , ~