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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
|
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 |
|
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 |
|
|
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 |
|
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. |
|
|
|
|