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Chapter III Affected Environment and Environmental Consequences 28 The results of Reclamation's computer modeling of the Lake, with and without temperature controls are shown in Figures 7 and 8 for the summer and winter seasons, respectively. The analysis includes a series of graphs at various locations in Lake Powell. As can be seen in the two figures, warmwater releases from the lake would have almost no impact on surface water temperatures during the late summer or winter seasons. Of particular interest, Figure 8 shows the modeled impact of warm water releases on winter temperatures in Lake PowelL Warmwater releases have almost no affect on surface temperatures (less than 1 oc) where the threadfm shad winter. Some cooling is observed in the deeper layers. Temperatures would be cooler with temperature controls at depths between 100 feet and 250 feet during the winter. This should have little effect on the fishery. Reservoir Evaporation - Evaporation in Lake Powell is about 0.5 MAF per year and about 0.7 MAF per year in Lake Mead. The computer modeling studies conducted by the Denver Technical Service Center (TSC) show that the relatively small volume of warmwater releases will have little impact on the heat budget of Lake Powell. With little or no change expected in surface temperatures, no measurable change in evaporation is expected for either Lake Powell or Lake Mead. Salinity - Salinities in the range typically found below Glen Canyon Dam (400-600 mg/L) have extremely little impact on the environment. The natural ecosystem was well adapted to survive salinities that exceeded 1,200 mg/L. Salinity is a concern further downstream where it can impact plumbing and salt sensitive crops. With closure of Glen Canyon Dam in the mid-I960s, the variation of salinity dropped significantly. The surface layer in Lake Powell has the lowest salinity levels found in the lake. The proposed action would release water from the surface during the summer months, reducing downstream salinity. The balance of the year would see slightly higher release salinities. The net effect will be to increase the seasonal variation of salinity releases from the dam. Maximum salinity of the river below the dam would not approach levels which might impact fish and wildlife. Salinity Below Glen Canyon Dam 1400 ~ 1200 0 Cl g 1000 >. "" 800 .5 lii 600 (/) >. :c 400 - c o 200 :::!: o o 1940 1960 1980 2000 Figure 9- The annual variation in salinity was greatly reduced in the mid- I 960s by the buffering effect of reservoir storage, The Colorado River Basin Water Quality Standards require the maintenance of long-term salinity conditions in the Colorado River at three stations: below Hoover Dam, below Parker Dam, and at Imperial Dam. Seasonal, even annual variations in salinity do not impact