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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem (1999)
Commission on Geosciences, Environment and Resources (CGER)

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189
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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem

Appendix E
Table II-7 Summary Comparison of Alternatives and Impacts

 Page
189

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem Appendix E Table II-7 Summary Comparison of Alternatives and Impacts

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem This page in the original is blank.

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem Table II-7. — Summary Comparison of Alternatives and Impacts   No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow WATER Streamflows (1,000 acre-feet) Annual streamflows Median annual release 8,753 8,573 8,559 8,559 Monthly streamflows (median) Fall (October) 568 568 568 568 Winter (January) 899 899 899 899 Spring (May) 587 587 592 592 Summer (July) 1,045 1,045 1,045 1,045 Hourly streamflows can be found in table 11-2. SEDIMENT Riverbed sand (percent probability of net gain) After 20 years 50 49 53 61 After 50 years 41 36 45 70 Sandbars (feet) Active width 44 to 74 47 to 77 33 to 53 28 to 47 With habitat maintenance flows       41 to 66 Potential height 10 to 15 10 to 16 7 to 11 6 to 10 With habitat maintenance flows       9 to 14 FISH Aquatic food base Limited by reliable wetted perimeter Same as no action Minor increase Moderate increase Native food Stable to declining Same as no action Same as no action Same as no action Non-native warmwater and coolwater fish Stable to declining Same as no action Same as no action Same as no action Interactions between native and non-native fish Some predation and competition by non-natives Same as no action Same as no action Same as no action

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow Trout Stocking-dependent Same as no action Same as no action Increased growth potential, stocking-dependent   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow WATER Streamflows (1,000 acre-feet) Annual streamflows           Median and annual release 8,559 8,559 8,559 8,554 8,578 Monthly streamflows (median)           Fall (October) 568 568 568 492 699 Winter (January) 899 899 899 688 703 Spring (May) 592 592 592 1,106 699 Summer (July) 1,045 1,045 1,045 768 699 Hourly streamflows can be found in table 11-2. SEDIMENT Riverbed sand (percent probability of net gain) After 20 years 64 69 71 71 74 After 50 years 73 76 82 82 100 Sandbars (feet)           Active width 24 to 41 24 to 41 10 to 19 16 to 29 0 With habitat maintenance flows 41 to 66     37 to 60   Potential height 6 to 9 6 to 9 3 to 5 4 to 7 0 to 1 With habitat maintenance flows 9 to 14     8 to 13   FISH Aquatic Fish Base Potential major increase Potential major increase Major increase Major increase Major increase

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow Native Food Potential minor increase Potential minor increase Uncertain potential minor increase Uncertain potential minor increase Uncertain potential minor increase Non-native warmwater and coolwater fish Potential minor increase Potential minor increase Potential minor increase Potential minor increase Potential minor increase Interactions between native and non-native fish Potential minor increase in warm, stable microhabitats Potential minor increase in warm, stable microhabitats Potential minor increase in warm, stable microhabitats Potential minor increase in warm, stable microhabitats Potential minor increase in warm, stable microhabitats Trout Increased growth potential, stocking-dependent Increased growth potential, stocking-dependent Increased growth potential, possibly self-sustaining Increased growth potential, possibly self-sustaining Increased growth potential, possibly self-sustaining

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow VEGETATION Woody plants (area) New high water zone No net change 0 to 9% reduction 15 to 35% increase 23 to 40% increase With habitat maintenance flows       0 to 12% increase Species composition Tamarisk and others dominate Tamarisk and others dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Emergent marsh plants New high water zone         Aggregate area of wet marsh plants No net change Same as no action Same as or less than no action Same as or less than no action WILDLIFE AND HABITAT Riparian habitat See vegetation.       Wintering waterfowl (aquatic food base) Stable Same as no action Same as no action Potential increase ENDANGERED AND OTHER SPECIAL STATUS SPECIES Humpback chub Stable to declining Same as no action Same as no action Same as no action Razorback sucker Stable to declining Same as no action Same as no action Same as no action Flannelmouth sucker Stable to declining Same as no action Same as no action Same as no action Bald eagle Stable Same as no action Same as no action Potential increase Peregine falcon No effect No effect No effect No effect Kanab ambersnail No effect Some incidental take Some incidental take Some incidental take Southwestern willow flycatcher Undetermined increase Same as no action Same as no action Same as no action

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow VEGETATION Woody plants (area) New high water zone 30 to 47% increase 30 to 47% increase 45 to 65% increase 38 to 58% increase 63 to 94% increase With habitat maintenance flows 0 to 12% increase     0 to 12% increase   Species composition Tamarisk, coyote willow, arrowweed, and camelthorn dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Tamarisk, coyote willow, arrowweed, and camelthorn dominate Emergent marsh plants New high water zone           Aggregate area of wet marsh plants Same as or less than no action Same as or less than no action Less than no action Less than no action Less than no action WILDLIFE AND HABITAT Riparian habitat See vegetation.         Wintering waterfowl (aquatic food base) Potential increase Potential increase Potential increase Potential increase Potential increase ENDANGERED AND OTHER SPECIAL SPECIES Humpback chub Potential minor increase Potential minor increase Uncertain potential minor increase Uncertain potential major increase Uncertain potential minor increase Razorback sucker Potential minor increase Potential minor increase Uncertain potential minor increase Uncertain potential minor increase Uncertain potential minor increase Flannelmouth sucker Potential minor increase Potential minor increase Uncertain potential minor increase Uncertain potential major increase Uncertain potential minor increase Bald eagle Potential increase Potential increase Potential increase Potential increase Potential increase Peregrine falcon No effect No effect No effect No effect No effect Kanab ambersnail Some incidental take Some incidental take Some incidental take Some incidental take Some incidental take Southwestern willow flycatcher Same as no action Same as no action Same as no action Same as no action Same as no action

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow CULTURAL RESOURCES Archeological sites (Number affected) Major (336) Major (336) Potential to become major (263) Moderate (Less than 157) Traditional cultural properties Major Same as no action Potential to become major Moderate Traditional cultural resources Major Same as no action Same as no action Increased protection AIR QUALITY Regional air quality Total emissions (thousand tons)       Sulfur dioxide 1,960 Same as no action Slight reduction Slight reduction Nitrogen oxides 1,954       RECREATION Fishing Angler activity Potential danger Same as no action Same as no action Moderate improvement Day rafting Navigation past 3-Mile Bar Difficult at low flows Same as no action Negligible improvement Major improvement White-water boating Safety High risk at very high and very low flows Same as no action Negligible improvement Minor improvement Camping beaches (average area at normal peak stage) Less than 7,720 square feet Same as no action Same as no action Minor increase Wilderness values Influenced by range of daily fluctuations Same as no action Minor increase Moderate increase Economic benefits Change in equivalent annual net benefits (1991 nominal $ million) 0 0 0 +0.4

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem     No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow Present value (1991 $ million) 0 0 0 +4.6   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow CULTURAL RESOURCES Archeological sites (Number affected) Moderate (Less than 157) Moderate (Less than 157) Moderate (Less than 157) Moderate (Less than 157) Moderate (Less than 157) Traditional cultural properties Moderate Moderate Moderate Moderate Moderate Traditional cultural resources Increased protection Increased protection Increased protection Increased protection Increased protection WILDLIFE AND HABITAT Regional air quality Total emissions (thousand tons)       Sulfur dioxide Slight reduction Slight reduction Slight reduction Slight reduction Slight reduction Nitrogen oxides           RECREATION Fishing Angler safety Moderate improvement Moderate improvement Major improvement Major improvement Major improvement Day rafting Navigation past 3-mile bar Major improvement Major improvement Major improvement Major improvement Major improvement

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow White-water boating Safety Minor improvement Minor improvement Moderate improvement Potential to become major increase Major improvement Camping beaches (average area at normal peak stage) Minor increase Minor increase Major increase Potential to become major increase Major increase Wilderness values Moderate to potential to become major increase Moderate to potential to become major increase Major increase Major increase Major increase Economic benefits Change in equivalent annual net benefits (1991 nominal $ million) +3.7 +3.9 +3.9 +4.8 +2.9 Present value (1991 $ nominal million) +43.3 +45.6 +45.6 +55.0 +23.5

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem     No Action Maximum Powerplant Capacity High Fluctuating Flow Moderate Fluctuating Flow POWER Annual economic cost 1991 nominal $ million           Hydrology   0 -1.5 2.1 54.0 Contract rate of delivery   0 0 2.5 36.7 Present value (1991 $ million)           Hydrology   0 -17.3 24.3 624.5 Contract rate of delivery   0 0 28.9 424.5 Wholesale rate   18.78 18.78 19.38 22.82 (1991 mills/kWh)       (+3.2%) (+21.5%) Retail rate (1991 mills/kWh) 70% of end users   No change No change No change to slight decrease No change to slight decrease 23% of end users   No change No change Slight decrease to moderate increase Slight decrease to moderate increase 7% of end users (weighted mean)   64.1 64.1 64.6 (+0.8%) 69.7 (+8.8%) NON-USE VALUE No data.           Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow POWER Annual economic cost 1991 nominal $ million Hydrology 15.1 36.3 65.9 88.3 69.7 Contract rate of delivery 44.2 35.6 68.7 123.5 85.7

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Downstream: Adaptive Management of Glen Canyon Dam and the Colorado River Ecosystem   Modified Low Fluctuating Flow Interim Low Fluctuating Low Existing Monthly Volume Steady Flow Seasonally Adjusted Steady Flow Year-Round Steady Flow Present value (1991 $ million)           Hydrology 174.6 418.7 761.4 1,021.2 805.0 Contract rate of delivery 511.2 411.7 794.6 1,428.4 991.2 Wholesale rate 23.16 23.18 25.22 28.20 26.78 (1991 mills/kWh) (+23.3%) (23.4%) (34.4%) (+50.2%) (+42.6%) Retail rate (1991 mills/kWh) 70% of end users No change to slight decrease No change to slight decrease No change to slight decrease No change to slight decrease No change to slight decrease 23% of end users Slight decrease to moderate increase Slight decrease to moderate increase Slight decrease to moderate increase Slight decrease to moderate increase Slight decrease to moderate increase 7% of end users (weighted mean) 70.5 (+10.0%) 70.2 (+9.6%) 72.9 (+13.8%) 75.8 (+18.4%) 74.5 (+16.3%) NON-USE VALUE No data.        

Representative terms from entire chapter:

fluctuating flow