HOOVER POWERPLANT MODIFICATION FEASIBILITY REPORT
APPENDIX C
HYDROLOGY
MAY 1981
PREPARED BY BUREAU OF RECLAMATION LOWER COLORADO REGION
APPENDIX C - HYDROLOGY
TABLE OF CONTENTS
Page
I. INTRODUCTION .....C-1
A. Purpose .....C-1 B. Background .....C-1 C. Location .....C-1 D. Climate .....C-1 E. Alternatives Considered .....C-1
1. Surface ...... C-1 2. Underground Powerhouse .....C-1 3. Replacement of Units A8 and A9 .... C-2 4. Pumped-Back Storage .....C-2
II. WATER SUPPLY AND RESERVOIR OPERATION .....C-3
A. Present Condition .....C-3
1. Water Supply .....C-3
a. Runoff .....C-3 b. Demands .....C-3
2. Reservoir Operation .....C-5
a. Control of River Operations .....C-5 b. Forecasted Water Supply .....C-6 c. Scheduled Annual Water Requirements . . C-7 d. Daily Water Requirements .....C-8 e. Daily Operations .....C-8 f. Water Scheduling - Power Generation Relationship .....C-9 g. Historic Operational Data .....C-10 h. Weekly Release Patterns .....C-12
B. Future Conditions .....C-13
1. Water Supply .....C-13
a. Runoff .....C-13 b. Demands .....C-17
2. Reservoir Operation .....C-17 3. Lake Mohave Operation Study .....C-27
a. Study Results .....C-29 b. Study Evaluation and Conclusions . C-30
C-i TABLE OF CONTENTS (continued)
Page
III. TAILWATER STUDIES ...... C-32
A. Introduction ...... C-32 B. Design Discharges C-32 C. Water Surface Profiles ...... C-34
1. Cross Sections ...... C-34 2. Steady Flow Tailwater Study ...... C-35 3. Calibration of Unsteady Flow Model ...... C-35 4. Calibration of 1979 Steady Flow Model ...... C-38 5. Projections for Additional 500-MW Powerhouse ...... C-44 6. Projections for Other Alternatives ...... C-48
D. Cofferdam Studies ...... C-53
1. Introduction ...... C-53 2. Cofferdam Studies No. 1 and No. 2 ...... C-53 3. Cofferdam Study No. 3 ...... C-53 4. Cofferdam Study No. 4 ...... C-54
E. Hoover Powerplant Modification Degradation Study C-55
1. Introduction ...... C-55 2. Present Channel Conditions ...... C-55 3. Degradation Analysis ...... C-55 4. Conclusions ...... C-58
F. Proposed Powerhouse Discharge Study ...... C-59
1. Introduction ...... C-59 2. Analysis ...... C-59 3. Conclusions ...... C-60
G. Head Loss Study ...... C-60
1. Introduction ...... C-60 2. Analysis ...... C-60 a. 500-MW Powerplant ...... C-60 b. A8 and A9 Alternative ...... C-64
3. Conclusion ...... C-64
C-ii TABLE OF CONTENTS (continued)
Page
IV. WATER TEMPERATURE STUDIES ...... C-65
A. Discharge Temperature Study ...... C-65
1. . Introduction ...... C-65 2. -Analysis ...... C-65 3. Conclusions ...... C-73
B. River-Lake Interface Study ...... C-74
1. Introduction ...... C-74 2. Analysis C-74 3. Conclusions ...... C-75
C. Ground-Water Conditions at Willow Beach National Fish Hatchery ...... C-75 1. Introduction C-75 2. Available Data ...... C-75 3. Conclusions ...... C-76
BIBLIOGRAPHY ...... C-78
LIST OF TABLES
No. Page
1 Colorado River Transit Times ...... C-9
2 Physical Characteristics - Hoover Dam and Powerplant . . C-11
3 Physical Characteristics - Davis Dam and Powerplant. . . C-11
4 Low Discharge Extremes at Hoover Dam ...... C-12
5 CRSP Hydrologic Sequences ...... C-14
6 Estimated Future River Losses and Gains Lower Colorado River Hoover Dam to the Northerly Internationl Boundary (NIB) ...... C-18
7 Consumptive Use of Diversions from Mainstream, States of Arizona and Utah above HoovPr Dam and Hoover Dam to Parker Dam C-19
8 Consumptive Use of Diversions from Mainstream, State of Arizona, Parker Dam to Imperial Dam ...... C-20
C-iii TABLE OF CONTENTS (continued)
LIST OF TABLES (continued)
No. Page
9 Consumptive Use of Diversions from Mainstream, State of Arizona, Imperial Dam to NIB and below .....C-21
10 Consumptive Use of Diversions from Mainstream, State of California from Nevada-California Boundary to Parker Dam .....C-22
11 Consumptive Use of Diversions from Mainstream, State of California, Parker Dam to Imperial Dam .....C-23
12 Consumptive Use of Diversions from Mainstream, State of California, Imperial Dam to NIB .....C-24
13 Consumptive Use of Diversions from Mainstream, State of Nevada, above Hoover Dam to Nevada-California Boundary .....C-25
14 Peak Discharges .....C-34
15 Colorado River Cross Sections .....C-36
16 PSEUDO Calibration Results .....C-37
17 Calibration Coefficients .....C-39
18-21 Calibration Results .....C-40-43
22 Projected Peak Water Surface Elevations With Lake Mohave at 647 feet .....C-45
23 Projected Peak Water Surface Elevations With Lake Mohave at 630 feet ...... C-45
24 Hoover Mod Peak Velocities vs. Current Peak Velocities .....C-47
25 Peak Velocities .....C-48
26 Other Alternatives ...... C-49
27 Computed Lake Mohave Elevations ...... C-50
28 Maximum Possible Reverse Flows ...... C-51
29 Storage Provided by Control Dam ...... C-52
C-iv TABLE OF CONTENTS (continued)
LIST OF TABLES (continued)
No. Page
30 Maximum Water Surface Elevations (feet) ...... C-54
31 Minimum Particle Size Required to Armor ...... C-58
32 Tailbay Elevations ...... C-60
33 Penstock Velocities ...... C-61
34 Friction Loss Modified Condition ...... C-6I
35 Friction Loss - Uprated Condition ...... C-62
36 Cumulative Head Loss ...... C-62
37 Capacity Reduction ...... C-63
38 Penstock Flow Distribution ...... C-67
39 Water Density ...... C-68
40 Upper Limit of Withdrawal Zone for Upper Orifice . C-69
41 Lower Limit of Withdrawal Zone for Upper Orifice . • • C-70
42 Velocity Distribution - Upper Orifice • • • O O O O O C-72
43 Observed Interface Data ...... C-75
44 Ground Water Conditions at Willow Beach Area ...... C-77
LIST OF FIGURES Following No. Page la River Operation Data Hydrographs - Hoover Dam and Lake Mead ...... C-10 lb River Operation Data Hydrographs - Hoover Dam and Lake Mead ...... C-10
2a River Operation Data Hydrographs - Davis Dam and Lake Mohave ...... C-12
2b River Operation Data Hydrographs - Davis Dam and Lake Mohave ...... C-12
C- v TABLE OF CONTENTS (continued)
LIST OF FIGURES (continued)
Following No. Page
2c River Operation Data Hydrographs - Davis Dam and Lake Mohave ...... C-12
3 Hoover Dam Weekly Discharge Schedule - Spring Season . . C-12
4 Hoover Dam Weekly Discharge Schedule - Summer Season . . C-12
5 Hoover Dam Weekly Discharge Schedule - Fall Season . . C-12
6 Hoover Dam Weekly Discharge Schedule - Winter Season . . C-12
7a Lake Mead Elevation under 15 Different Hydrologic Sequences (1980-2040) ...... C-15
7b Lake Mead Elevation under 2 Different Hydrologic Sequences (1980-2040) ...... C-15
8 Hoover Dam Weekly Load Curve - Summer Season ...... C-26
9 Hoover Dam Weekly Discharge Schedule - Spring Season - Uprated Condition ...... C-26
10 Hoover Dam Weekly Discharge Schedule - Spring Season . . C-26
11 Hoover Dam Weekly Discharge Schedule - Summer Season . . C-27
12 Hoover Powerplant Tailwater Curve ...... C-32
13 Colorado River Cross Sections - (22 Drawings) ...... C-34
14 Map of Colorado River Cross Sections C-36
15 Hoover Modification Gage Location Map ...... C-37
16 Hoover Modification Test Release Schedule ...... C-37
17 Colorado River Elevation Gage No. 5 ...... C-38
18 Water Surface Profiles, Lake Mohave at 630 ...... C-43
19 Water Surface Profiles, Lake Mohave at 647 . . C-44
20 Water Surface Profiles, Lake Mohave at 630 ...... C-45
21 Water Surface Profiles, Lake Mohave at 630 ...... C-46
C-vi
TABLE OF CONTENTS (continued)
LIST OF FIGURES (continued)
Following No. Page
22 Water Surface Fluctuation at Hoover Tailbay, Lake Mohave at 630 ...... C-46
23 Water Surface Fluctuation at Hoover Tailbay, Lake Mohave at 647 ...... C-46
24 Water Surface Fluctuation at Willow Beach, Lake Mohave at 630 ... C-46
25 Water Surface Fluctuation at Willow Beach, Lake Mohave at 647 .... C-46
26 Typical Velocity Distribution .....C-47
27 Water Surface Profiles for Other Alternatives .....C-49
28 Water Surface Profiles for Other Alternatives .....C-49
29 Water Surface Profiles for Other Alternatives .....C-49
30 Section for 105' High Cloverleaf Cofferdam No. 3 . . C-53
31 A8 and A9 Cofferdam .....C-54
32 Competent Bottom Velocity vs. Transportable Sediment Size .....C-56
33 Tractive Force vs. Transportable Sediment Size .....C-57
34a- Lake Mead Temperature and Conductivity .....C-65 34d
35 Elevation of Intake Gates ...... C-68
36 Definition Sketch of Variables for Orifice Flow • • • C-68
37 Interface Location Curves ...... C-74
C-vii TABLE OF CONTENTS (continued)
Page
APPENDED MATERIAL .... C-80
Appended Tables
No.
A-1 Annual Releases from Glen Canyon A-2 Hoover Releases A-3 Lake Mead Water Surface Elevation A-4 Powerplant Generation at Hoover Dam A-5 Hoover-Lake Mead Operation Plan-2020 A-6 Monthly Energy Breakdown-1986 A-7 Monthly Energy Breakdown-1996 A-8 Monthly Energy Breakdown-2033 A-9 Davis-Lake Mohave Operation Plan-1986 A-10 Hoover-Lake Mead Operation Plan-1986 A-11 Davis-Lake Mohave Operation Plan-1996 A-12 Hoover-Lake Mead Operation Plan-1996 A-13 Davis-Lake Mohave Operation Plan-2033 A-14 Hoover-Lake Mead Operation Plan-2033 A-15 Verification of Mathematical Model A-16 Summary of Daily Operation Studies-1986 A-17 Summary of Daily Operation Studies-2033 A-18 Summary of Daily Operation Studies-1996
Appended Figures
No.
A-1 Projected Effects of Modified Hoover Powerplant Releases Upon Lake Mohave Stage
C-viii I. INTRODUCTION
A. Purpose
The purpose of this Hydrology Appendix is to provide a detailed presentation of the hydrologic studies performed 'during the feasi- bility investigation of the 'Hoover Powerplant Modification Project.
B. Background
A hydroelectric powerplant can provide peaking power at a significantly lower coit thin most other types of powerplants. This study investigated the feasibility of increasing the peaking capacity of the Hoover'hydroelectric powerplant with the 'purpoSe of helping to meet the need for peaking power in an economical Way:
Hoover Powerplant currently has a peak nameplate generating capacity of 1,340 megawatts (MW). As part.of the operation and main- tenance program, the 'generatOrs'are being uprated to a peak nameplate generating capacity of about 1,800 MW. This study considered various Means of increasing the capacity of the powerplant beyond the uprated capacity of 1,800 MW. After a cursory evaluation of numerous Possi- bilities, the investigation concentrated on additions of 260 MW and 500 MW of capacity. '
C. Location
The project area is at Hoover Dam and Powerplant, located in the Black Canyon of the Colorado River on the Arizona-Nevada border, 25 miles southeast of Las Vegas, and 7 miles northeast of Boulder City, Nevada. (See frontispiece location map.) The dam is about halfway between Lee Ferry, the dividing point' between the Upper and Lower Basins, and the Girlf of California, and the Colorado River's natural outlet'to the sea.
D. Climate
The climate of the project area is presented in the Plans and Estimates Appendix.
E. Alternatives Considered
1. Surface Powerhouse. This alternative would require the construction of an additional powerhouse located adjacent to the downstream end of the existing Arizona powerhouse. It would consist of two units each having a naleplate capacity of 250 MW, for a total additional capacity of 500 MW.
2. Underground Powerhouse. The only difference between this alternative and the surface powerhouse is that it would be located underground, behind the existing Arizona powerhouse.
C-1 3. Replacement of Units A8 and A9. A net increase in capacity of 260 MW could be achieved by replacing units A8 and A9 with a *single 350-MW unit. These two units are the smallest in the powerplant.
4. Pumped-Back Storage. Peaking capacity could be increased by installing reversible pump turbines. During the night and on weekends when there is a low demand for peaking capacity, these turbines could pump water from Lake Mohave back up into Lake Mead. Energy for pumping could be obtained from other powerplants that operate most.efficiently at a constant rate which is higher than the demand during the night and on weekends.
C-2 II. WATER SUPPLY AND RESERVOIR OPERATION
A. Present Condition
1. Water Supply
a. Runoff. The record of inflows into Lake Mead is divided into three periodsdue to the construction of Glen Canyon Dam. The average annual 'inflow into Lake Mead from 1935-62 was 11,830,099 acre-feet per year (ac-ft/yr) as recorded at the Grand Canyon'Gage.=' In 1962 Glen Canyon Dam, upstream of Lake Mead, was completed' and began filling in March' 1963, reducing inflowi to Lake Mead to 2,740,000 ac-ft/yr for the next:2 years. Men from 1965-78, with Glen Canyon Dam following a more gradual filling schedule, the average annual inflow to Lake' Mead was 9,170,000 ac-ft/yr. The average,Annual discharge below Hoover Dam, built in 1935, into Lake Mohave- from 1935-78 'was 9,570,000 ac-ft/yr.
b. Demands. In a normal water year the maximum amount of water that the lower basin states are apportioned to receive is 7.5 million acre-feet (MAF). However, these states cannot physically divert this full amount until the Central Arizona Project is capable of diverting a full water supply. The following tabulation shs how this water is divided between' California, Arizona, and Nevada=' and also an additional annual guarantee of 1.5 MAF for Mexico.
Lower Colorado River Basin Apportionments
California 4.4 MAF Arizona 2.8 MAF Mexico 1.5 MAF Nevada 0.3 MAF
Total 9.0 MAF
The tributary inflow below Compact Point is not considered Colorado River water until it enters the'Colorado River channel. The States may use this tributary water before it reaches the Colorado River without it being changed to their mainstream diversion.
Currently Arizona and Nevada cannot use their full apportion- ment so California and Mexico have been using some of their water as shown in the following tabulation:
1/ Minor tributary inflows below the Grand Canyon gage were not considered. 2/ Lake Mohave was created in 1950 when Davis Dam was constructed. I/ According to the Boulder Canyon Project Act of 1928.
C-3 / Lower Colorado River Main Stem Consumptive Use 1 (million acre-feet)
User 1976 1977 1978
California 4.71 5.10 4.50 Arizona 1.25 1.23 1.23 Mexico 1.77 1.78 1.73 Nevada 0.07 0.07 0.07
7.80 8.18 7.53
According to Item 6, Section 2 of the Arizona vs. California Supreme Court Decree of 1964, the Central Arizona Project(CAP), scheduled to come on line in 1985, will make it possible for Arizona to consume a much larger portion of its full apportionment. Water in excess of the users demands must be released ih order to account for reach loss and regulatory waste.
A list of the major water users in each state is presented as follows: Major Arizona Water Users
1. Lake Mead National Recreation Area 2. Davis Dam and Government Camp 3. Mohave Valley Irrigation and Drainage District 4. Fort Mohave Indian Reservation 5. Havasu National Wildlife Refuge 6. Lake Havasu Irrigation and Drainage District 7. Town of Parker 8. Colorado River Indian Reservation 9. Cibola National Wildlife Refuge 10. Imperial National Wildlife Refuge 11. Yuma Proving Ground 12. North Gila Valley Irrigation District 13. Warren Act Contractors Outside Gila Project 14. Wellton-Mohawk Irrigation and Drainage District 15. Yuma Irrigation District 16. Yuma Mesa Irrigation and Drainage District 17. Unit "B" Irrigation and Drainage District 18. City of Yuma 19. Yuma County Water Users' Association 20. Cocopah Indian Reservation
1/ Decree Accounting Data - calendar year.
C-4 Major California Water Users
1. Fort Mohave Indian Reservation 2. City of Needles 3. San Bernadino County 4. Metropolitan Water District of Southern California 5. Parker Dam and Government Camp 6. Colorado River Indian Reservation 7. Palo Verde Irrigation District 8. City of Blythe ' 9. East Blythe County Water District 10. Yuma Project Reservation District 11. Imperial Irrigation District 12. Coachella Valley Water District 13. City of Winterhaven
Major Nevada Water Users
1. Boulder City 2. Lake Mead National Recreation Area 3. Basis Management, Inc. 4. City of Henderson 5. Las Vegas Valley Water District 6. Nevada State Department of Fish and Game 7. Pacific Coast Building Products, Inc. 8. City of North Las Vegas 9. Nellis Air Force Base 10. Southern California Edison Company
2. Reservoir Operation
a. Control of River Operations. The Secretary of the Interior or his designated representative (usually the Lower Colorado Regional Director), has effective control over Colorado River opera- tions and all releases from Lower Colorado River reservoirs. Ih the case of Hoover Dam and Powerplant, releases from Lake Mead are normally accomplished by declaration of monthly generation totals to the Hoover operating agents (the City of Los Angeles, Department of Water and Power, and the Southern California Edison Company). Usually the hourly (or 'even daily) Hoover discharges, except for infrequent situations, are at the discretion of the Hoover operating agents who themselves operate the generating facilities under contract with the United Statei. As would be expected, the operating agents release the quantity of waters needed to generate the energy schedule for the illottees during those days and' hours when their demand for peaking power is highest: The smaller powerplants at Davis Dam and Parker Dam are operated entirely by Federal 'employees, so releases at those locations are at all times under Federal contrOl.
C-5 If conditions warrant, the Secretary's representative may request the operating agents to adhere to a specific energy schedule, the operating agents have 3 days from receipt to comply. If either shall fail to comply as determined by the Secretary's representative, under the provisions of the Boulder Canyon Project Act and the related power contracts, he has authority to take charge of such operation of the powerplant facilities as he deems necessary until his action is modified or the operating agents are reinstated. The latter has never been required, although written request for compliance has been necessary on two different occasions. Normally, the Water Scheduling Branch, Division of Water and Land Operations of the Lower Colorado Region and the operating agents are able to coordinate integration of Hoover generation and water releases for downstream consumptive use and river regulation needs in a routine and fully satisfactory manner.
Water use along the Colorado River is controlled by more than 20 major legal actions, congressional acts, a United States Supreme Court decision, water and power contracts, intrabasinal compacts, and international treaty. 'Among these are the Colorado River Compact, Boulder Canyon Project Act, Mexican Treaty of 1944, and the Supreme Court Decree of March 9, 1964, in Arizona v. California. Collectively they make up the "Law, of the River" whichgoverns the management and operation of all dams and powerplants on the Lower Colorado River.
b. Forecasted Water Supply. Estimation of the water supply available for the Lower Colorado River Basin use begins in January of each year with forecasting the April-July Colorado River runoff at Lee Ferry, Arizona. This April-July forecast is the critical inflow volume for which updated estimates are prepared as of the first of each month, January through June. These forecasts are used for scheduling in order of descending priority: (1) flood control and river regulation releases; (2) irrigation and domestic uses, including the 'satisfaction of present perfected rights; and (3) power releases. The United States may, however, release water in satisfaction of its Treaty obligations to Mexico without regard to the priorities specified.
Formal determination of any water shortages and surpluses are made by the Secretary of the Interior after consultation with the Basin States. If the Secretary determines there is sufficient water available to satisfy 7,500,000 acre-feet of annual consumptive use by California, Arizona, and Nevada, then California receives 4,400,000 acre-feet, Arizona receives 2,800,000 acre-feet, and Nevada receives A0,000 acre-feet for their respective uses. In addition, Mexico receives 1,500,000 acre-feet for use in that country in satisfaction of the Treaty.
C-6 If the Secretary of the Interior declares a surplus of Colorado River water, the United States users and Mexico are notified that additional water is available. It is conceivable that in certain years enough water can be released from Hoover Dam to generate firm power and also secondary energy. Under present conditions, this could amount to approximately 850,000 acre-feet or more in excess of present downstream 'demands. If and when additional water is available, it is apportioned 50 percent to California an4,50 percent to Arizona. If the United States contracts with Nevada,—' then Arizona will receive 46 percent and Nevada 4 percent. If 'sufficient surplus water is available, the 1944 Treaty allows Mexico to schedule up to an addi- tional 200,000 acre-feet, which would increase Mexico's entitlement for that year to a maximum of 1,700,000 acre-feet. The additional release for Mexico and the States would generate firm and secondary power.
If it is determined that insufficient Colorado River water is available, then the Secretary, after providing for the satisfaction of present Perfected rights, may apportion the remaining available water for consumptive use as consistent with the Boulder Canyon Project Act. 1n noevent shall more than 4,400 1 000 acre-feet be apportioned to California including all present Perfected rights. If, however, water apportioned for consumptive use in a State will not be consumed in that State, the Secretary' may release such water for use in the other States. No rights to the recurrent use of such water accrue by such use.
c. Scheduled Annual Water Requirements. After the end of each water year the Upper and Lower Colorado Regions develop a pro- posed annual reservoir 'Operating plan which, with 4 complete report of Operations during the preceding year, is 'submitted to Congreis each January. Each November the Lower Colorado Regional Office forwards a request for monthly estimates for the coming year of the water require- ments by each water user organization contracting for water from the Colorado River below Hoover Dam. At the same time, a representative of the Regional Office contacts each water user organization to encourage Water conservation and discuss their water demands and the water supply for the coming year. At least once each calendar year, the ComMittee on Integration meet at the Boulder Canyon Project (Regional Office) for the purpose of programing integration of Hoover Powerplant operations, subject to the purposei of the Project Act. The Committee on Integration is comprised of three members; the repre- sentative of the Secretary of the Interior, and one repreientative of each of the two operating agents at Hoover Dam. The Committee then agrees upon a monthly operation schedule for releases and for power generation from Hoover 'Dam for the current year. (Surpluses or shortages in the actual available water supply may later require modifications by mutual consent of the Secretary A the operating agents.)
1/ An amendatory contract is currently in a state of development by the Bureau of Reclamation.
C-7 d. Daily Water Requirements. Releases from Imperial, Parker, and Davis Dams are scheduled on a daily basis to meet the incoming orders from the water users.
The Bureau of Reclamation (Bureau) is responsible for scheduling daily Parker Dam releases and for making any required changes in those releases necessary for the efficient operation of the Lower Colorado River from Hoover Dam to the International Boundary with Mexico, along with all computations necessary for the issuance of the "Master Schedule of Flows and Diversions at Imperial Dam" and a separate schedule, "Control Schedule of Colorado River at and below Yuma, Arizona." The Bureau's duties also include responsibilities for operation of Senator Wash Pumping-Generating Plant and Regulating Reservoir and sluicing operations associated with the operation of Laguna Dam and Reservoir.
Water orders are received each Wednesday for the anticipated daily water requirements for the following week from the agencies in the United States contracting for the delivery of water from Imperial Dam and for requirements under the Mexican Water Treaty from the Yuma Office of the International Boundary and Water Commission.
The Bureau prepares weekly master schedules of Lower Colorado River flows and diversions and these schedules are distributed each Friday by the Bureau's Water Scheduling Branch at Boulder City, Nevada. The schedules are based on irrigation require- ments in the United States, requests for delivery of water under the Mexican Water Treaty, and *requirements for river regulation, coordinated with flood control and power operations, to obtain the optimum overall efficiency from the a■iailable riverf low.
e. Daily Operations. The daily water scheduling operation is essentially one of adjustment. Releases of water from Hoover, Davis, and Parker Dams are made pursuant to the total orders from the individual water users, but changes primarily in weather conditions may cause water supply and irrigation needs to vary significantly between the time of release and the scheduled time of diversion downstream. Because of the distance the water must travel, water users normally must schedule orders 3 days in advance of need. Table 1 illustrates the approximate water transit times on the Lower Colorado River.
C-8 Table 1 COLORADO RIVER TRANSIT TIMES Hoover Dam to Northern International Boundary Hoover Powerplant Modification Project
Approximate• First Effect Transit Time Reach (Hours) =1
Hoover Dam to Davis Dam 6 Davis Dam to Parker Dam 24 Parker Dam to Palo Verde Diversion Dam 24 Palo Verde Diversion Dam to Taylor Ferry 8 Taylor Ferry to Gaging Station below Cibloa Valley 8 Gaging Station below Cibola Valley to Imperial Dam 32 Imperial Dam to Yuma Gaging Station 8 Yuma Gaging Station to Northern International Boundary 4 All-American Canal, Imperial Dam to East Highline Canal 6
The Water Scheduling Branch uses both its time-sharing and process computer facilities for both formulation and daily adjustment Of weekly *water schedules. To compensate for major daily change orders, water is reregulated in Lake Mohave and Lake Havasu. Once allowed to pass Parker Dam3 however, no further major reregulation exists. To the extent possible, any *water "ordered but not taken" is delivered to other useri in satisfaction of their requirements or is delivered to storage. Minor excess waters can be salvaged by pumping to Senator Wash Reservoir (usable capacity 12,250 acre-feet). • If capacity is unavailable or water is not taken by Others, surpluses are pissed on to Mexico. Waters that reach Mexico in excess of scheduled treaty requirements are identified but are not charged against the scheduled treaty delivery. f. Water Scheduling - Power Generation Relationship. Water scheduling is accomplished under the priorities mentioned earlier and which were confirmed by the Arizona v. Calfornia Supreme Court Decree. From an energy generation standpoint, Article of the Colorado River Compact specifically states:
1/ The time required for Hoover releases to affect Lake Mohave depends upon its stage. When Lake Mohave is above elevation 633, lake conditions extend to the Hoover tailrace and releases from Hoover Dam begin to raise the upstream portion of Lake Mohave immediately.
C-9 "Subject to the provisions of this compact, water of the Colorado River System may be impounded and used for the generation of electrical power, but such impounding and use shall be subservient to •the use and consumption of such water for agriculture and domestic purposes and shall not interfere with or prevent use for such dominant purposes."
Although reservoir regulation for power generation is secondary to both downstream consumptive use and flood control con- siderations, the Hoover Dam operating agents do have operational flexibility. As long as the total monthly and annual generation schedule is met, the daily releases may usually be regulated by the allottees on an hourly basis to meet, as nearly as possible, peakload power requirements.
Also, when feasible, minimal offpeak flows from Hoover Dam are released so live stream conditions can be maintained below Hoover Dam. This consideration does not exist when the stage of Lake Mohave is higher than elevation 633, as Lake Mohave waters back up essentially to the tailrace of Hoover Dam. The Bureau tries2 ta maintain a release of about 2,000 cubic feet per second (ft Is) minimum in the reaches below Davis and Parker Dams to provide a live stream for fish and wildlife purposes.
Another factor bearing on Hoover peaking operations is that adequate storage capacity must be scheduled and available in Lake Mohave and in Lake Havasu in order to accommodate the amounts released from Hoover Dam. Ordinarily, this is considered and provided for in monthly and weekly reservoir operation schedules. The constraint nevertheless might exist if for some reason such as an electrical emergency the allottees would desire to deviate drastically from a scheduled release pattern.
Whenever conflicts arise in reservoir use, the Boulder Canyon Project Act requires that reservoir releases be accomplished under the previously mentioned priorities: (1) for flood control; (2) downstream consumptive uses; and (3) for power requirements.
g. Historic Operational Data. The plots in Figures la and lb show how the end of month contents in Lake Mead and the average monthly Hoover Dam discharges varied from 1935-77. Tables 2 and 3 supply data pertinent to the operating of Hoover and Davis Dams. The maximum recorded content of Lake Mead was 27,790,000 acre-feet at an elevation of 1220 feet on July 29, 1941, and the minimum was 10,695,000 acre-feet at an elevation of 1083 feet on April 26, 1956. The average discharge from Hoover Dam for the period from 1935-78 was 9,571,000 acre-feet per year.
C-10
80—YR. PROJECTED LAKE WAD ELEVATIONS (1980-2040) -15 DIFFERENT MAL= CONINTEN3 -WITH CAP STORAGE -OCT. 1979 SASE ALN OF CRSP IACEL
41:111IRC DEW SOW THAT WAD WU PROBABLY OE /MUM E.EVATEN UM FEET MOFE OFTEN TIW4 IT J. IE AT AM OTTER ELEVATION. 1250
, 'ET: 1200 --- No 4444FIONOWIGILLAityr AOlt 1,44 0 1150 \ AIL At JOIN I I g 1100
1060 1980 1990 2000 2010 2020
TIME (YEARS)
I GU RE 7A _
i figure 7b
Table 2 PHYSICAL CHARACTERISTICS - HOOVER DAM AND POWERPLANT Hoover Powerplant Modification Project
Elevation of top of dam ...... 1232 feet Maximum allowable reservoir elevation ...... 1229 feet Elevation at top of spillway gates ...... 1221.4 feet Crest elevation ...... 1205.4 feet Elevation needed for rated head = 476 with maximum tailbay elevation of 657 ...... 1133 feet with average tailbay elevation of 645 ...... 1121 feet Elevation needed for minimum power head = 420 with maximum tailbay elevation of 657 ..... 1077 feet with average tailbay elevation of 645 ..... 1065 feet Top of dead storage ...... 895 feet Active capacity, elevation 1229 to 895 ...... *29,248,000 acre-feet Capacity both spillways: 3 • Elevation 1229, gates raised . 63,000 ftl/s Elevation 1232, gates lowered 400,000 ft Is Capacity of outlet woks: 3 • River outlets (elevation 1221.4) 85,700 ft3/s Power outlets (elevation 1180) 40,600 ft /s
'Original capacity, does not take siltation into account.
Table 3 PHYSICAL CHARACTERISTICS - DAVIS DAM AND POWERPLANT Hoover Powerplant Modification Project
Elevation of top of dam ...... 655 feet Maximum allowable reservoir elevation ...... 647 feet Elevation at top of spillway gates ...... 647 feet Crest elevation ...... 597 feet Minimum operational elevation ...... 570 feet Top of dead storage ...... 533. 4 feet Active capacity, elevation 647 to 533.4 ...... 1,810,000 ace- feet Spillway capacity at elevation 647 ...... '214;000 ft Is Capacity of outlet works: River outlets (elevation 647) ...... 58,000 ft3/s Power outlets (elevation 640) ...... 26,500 ft'/s
C-11 The plots in Figures 2a through 2c show how the end of month contents in Lake Mohave and the average monthly Davis Dam discharges vary from 1950-77. The maximum recorded content of Lake Mohave was 1,811,000 acre-feet at an elevation of 647 feet on May 24, 1958, and May 29, 1963. The minimum was 1,168,000 acre-feet at an elevation of 622 feet, in September 1953.
Table 4 shows three of the most extreme periods of low discharge at Hoover Dam. Data for the period from 1976-79 were obtained from acoustical flowmeters located on each penstock. Before 1976, the data were obtained from totalizing flow meters on each turbine in the powerhouse.
Table 4 LOW DISCHARGE EXTREMES AT HOOVER DAM Hoover Powerplant Modification Project
Average Time Period Duration Discharge Dates Hours (Hrs.) (W/s). Reason
12/17-18/78 22:30-04:30 6 784 Moderate rains resulted in lower releases for the month.
2/10-19/79 19:30-97:00 203.5 1,479 Heavy side inflow from the Bill Williams and Gila Rivers resulted in lower releases.
1/9-29/74 18:00-00:00 462 3,587 Heavy rains in the irrigated areas resulted in lower releases.
h. Weekly Release Patterns. All the water discharged from Hoover Dam passes through the powerplant, except in times of flood control releases. The total *monthly Hoover generation needed to satisfy downstream requirements and regulating is set by the Bureau. The Hoover operating agents have the flexibility to release the water for generation whenever they want to long as they match the specified monthly generation and uo not deviate excessively during the month. Figures 3 through 6 show typical weekly release patterns for each season* of the year. As these figures show, Hoover is mainly used to supply peaking power and system regulation rather than baseload.
C-12
1962 454 45 JFMAMJJASOND JFMAMJJASONO JFMAMJJASONO JFMAMJJASOINO JfMAMJJASONDJFMAMJJASOND AIM OP • A 111111 11111 1 111 11111 1 111111111111111/11111111L1111111,MAillA
1 11111 1111111111111111WIL ASEELMICAIM11111111111110R11111111 1
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,0001.5. 3 3 900:2-4,0
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100 550 0 555.511
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1 0 0-560 550 0 —533.39
NOTES
Data shown hereon were obtained from water supply papers published by the Geological Survey UNITED STATES E...... OF TOM I NTERION MACAU OF RECLAN • TION REGION 3 RIVER OPERATION DATA HYDROGRAPHS DAVIS DAM AND LAKE MOHAVE COLORADO RivER
DRAWN _AMC ------SUMO TT , TRACED ------_ RECOMIPENDECIQ • colecAr.0__NAC______APPROVED.- 35 ,-300-123 FIGURE 2a
I • • ▪
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• Cd U • N 0 •
TO 40 SONYSII0141 NI 3821012210 "S'J'0 40 SONVSNON1 NI 3921/HOSI0 -- - -
n379 i974 t975 1976 1977 1979 ott • • • A • 44 A ND J A • • • • 36
34
32 4500 30 b100 28 VC* 26 -Available Contents VI 0 (End of month quantiti 1,200 VI 24 0 1■■•■ 4.420 w 1.100 S, 20 22 20 Poo Aviv/a 9. monthly Dpvis_ Do diseborge soo ,.•■■• 2 soo Reim 5 700 44 •0.; NI a 600 12 >■11E0 10 500 4
t_pm—r 6 300
4 200
see 2 100 *so 0 --..— sas .m1
19130 1961 1982 19133 1984 985 A • • • A • 365 • A • 36 000
34 1,7130 40 32 A00
30 MM. 00
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26 1,300
, 24 411■. 1,201 fa 10-449 IS 22 ',mow 1,100 8 2 20 Poe. 0 18 •■•••• 900 r.-•.0 44 IS i 6 800 z IS 0
i4 700 w-goo 0 DISCHARGE IN THOUSANDS OF CAS. 12 600 t i-svo 10 500
400 ISO 300
4 200
I 100 " ISO 0 555. MD
4 — I — 77 UPDATED. JANUARY 1971E TO MAW. 1977 300 UNITED STATES OEPARTMENT OF THE INTERIOR BUREAU OF RECLAIM T ION LOWER COLORADO REGION RIVER OPERATION DATA HYDROGRAPHS DAVIS DAM AND LAKE MOHAVE COLORADO RIVER
COMPILED IEL ...... SUBMITTED DRAFTE01'77.4.:LQ.91$14s .. RECOMMENDED ...... CHECKED ...... APPROVED ...... SIOULOER CI TY , NEV. 8 SHEET 3 41"1 351-300-123 I FIGURE 2c
Spring Season Present Condition (1340 MW) Figure 3 t
HOOVER DAM WEEKLY DISCHARGE
U - AT 1340 INS
0 - AT 1000 AM
• - Al 2300 IAN 65000
60000
55000 -
50000 -
45D00
40000 -
35000 -
30000 -
25000
20000•'
15000 -
10000
5000
1 1 4 4 4 12 24 36 48 60 72 84 96 108 120 132 144 155 168
TIME (HOURS)
Summer Season Present Condition (1340 MW) Figure 4 tšSt or(
Fall Season Present Condition (1340 MW) Figure 5
HOOVER DAM WEEKLY DISCHARGE
M - AT 1340 IAA
o - AT 1003 IAA
40 - Al 2300 IAN 65000
60000
55000
50000
45300
40000
35000
30000
25300
20000
15000
10000
5000
12 24 36 48 60 72 84 96 108 120 132 144 156 168
TIME (HOURS)
Winter Season Present Condition (1340 MW) Figure 6 I B. Future Conditions
1. Water Supply
a. Runoff. The average annual inflow into Lake Mead for the years 1980-2040 (61 years) will be approximately 9.4 MAF/yr according to the October 1979 base run of the Colorado River Storage Project (CRSP) mathematical model as shown in the appended material, Table A-1. The CRSP model does not directly compute the annual inflow into Lake Mead, instead it computes the discharge from Glen Canyon Dam, the tributary inflow between Glen Canyon Dam and Hoover Dam, and the' evaporation from Lake Mead. The tributary inflow is almost equal to the 'evaporation from Lake Mead. Therefore, for the purposes of this study; the discharge from Glen Canyon Dam, 9.4 MAF, can be used as the inflow to Lake Mead.
The projected annual discharges from Hoover Dam are shown on appended Table'A-2. The average annual discharge worked out to be 9.4 MAF/yr. Table A-3 (appended) 'shows the projected elevations of Lake Mead which average out to be about 1157 feet above mean sea level. The projected energy generated at Hoover Powerplant is shown on appended TableA-4. The average annual energy generation was esti- mated to be 4,124 MKWH.
The CRSP model used to predict this future water supply first became functional in 1965. It was the culmination of many hand studies for river operation, reservoir sizing, and water and power operations. These had been completed during the planning phase of the Colorado River Storage Project and also while the reservoirs were gaining significant power head. Gradually, decision blocks reflecting . experience and engineering were added to the basic model structure; which was at first little 'more than an automated hand study. During 1969 and early 1970, formal operating criteria were developed and the model was used to test these criteria and provide a basis for their acceptance by the states and others. These criteria provided operat- ing decisions which could be modeled. The model has been converted to the several computer systems employed by the Bureau. Its modeling range has been extended to Imperial Dam and salinity modeling from Glen Canyon Dam to Imperial has been added.
The model encompasses the Colorado River Storage Project in the Upper Basin, Lake Mead, and other facilities in the Lower Basin down to the last major diversion point within the boundaries of the United States.
Physical features of the system are described mathemati- cally. Distance and travel time are not applicable because the smallest time increment is 1 month. Other physical properties are incorporated or approximated in tl_ Aodel.
C-13 The CRSP model is an operations model. It will not describe individual project effects on tributaries to the main stem Colorado River, but Will show their downstream effects on quantity and quality of water in the river. It is not convenient nor practical to add new features or additional parameters. Its main purpose is to provide operating information on the ability of the Upper Basin to meet the Lee Ferry commitment to the Lower Basin. There were three components to this river system study: (1) the simulation model, a computer program, comprised of mathematical functions that maintain a water balance and operate the river within defined constraints; (2) water supply and salt loading data; and (3) projected depletion data.
The CRSP model simulates river operations in accordance with existing regulations established by Congress, court decree, and inter- national treaty. Water supply data input to the model consists of 15 different water supply canditions (sequences). The data in each sequence are not different (except for Sequences 1-3), but the order of the data is rearranged. Each water supply condition is identified by a sequence number and each is applied to a 61-year period of study beginning in water year 1980. Monthly flows from water year 1906 through Water year 1977 water supply data are developed from historic data. The first sequence applies wateryear 1906 flows to the first operating year (water year 1980). The next sequence applies 1911 flows to the first operating year. The periods of water supply data used in each sequence are listed in Table 5.
Table 5 CRSP HYDROLOGIC SEQUENCES Hoover Powerplant Modification Project
Sequence No. Water Supply Data Used
1 1906-66 2 1911-71 3 1916-76 4 1921-77 and 1906-09 5 1926-77 and 1906-14 6 1931-77 and 1906-19 7 1936-77 and 1906-24 8 1941-77 and 1906-29 9 1946-77 and 1906-34 10 1951-77 and 1906-39 U. 1956-77 and 1906-44 12 1961-77 and 1906-49 13 1966-77 and 1906-54 14 1971-77 and 1906-59 15 1976-77 and 1906-64
C-14 b. Demands. The CRSP model used future demand data, that were projected by the Water and Land Operations Division of the Bureau, to compute future discharges from Glen Canyon Dam, Hoover Dam, and Lake Mead elevations. Upper Basin depletions, assuming an average annual evaporation of 561,000 acre-feet, were estimated to total 4.0 million acre-feet in water year 1980 and 5.8 million acre-feet annually, by water year 2000. Lower Basin depletions excluding delivery to Mexico and Lake Mead evaporation, were estimated to be 6.1 million acre-feet in water year 1980 and 7.8 million acre-feet by water year 1986. These estimates of Lower Basin depletions include unmeasured return flow credit, reach losses and gains, and salvage below Hoover Dam.
In the future, Lower Basin (main stem) demands will change in two ways. Some existing users will increase their consumptive use and one new project will come online. Tables 6 through 13 show how the consumptive use of the major water users will vary from the year 1980 to 2030. The only new project is the Central Arizona Project (CAP) which is scheduled to start diverting water in 1985. CAP will not change Arizona's allocation of 2.8 MAF, but will cause Arizona to consume more of the 2.8 MAF than it has 'historically. So, in the future, the allocation of water to each state will not change, but the actual consumptive use will increase.
Two other new water consuming projects in the Lower Basin may begin to function in the next 10 years, besides CAP. However, these projects will not consume Colorado River water so their water use cannot be charged to the respective state's mainstream diversion. These two projects are listed in Table 7 as the Mogollon Project and the Warner Valley Projects. The Mogollon Project would supply water for Flagstaff, Arizona. The Warner Valley Project would provide a larger water supply for St. George, Utah.
All the demand data discussed in this section was incorporated in the CRSP model.
2. Reservoir Operation. The operation of Hoover and Davis Dams will change slightly in the future. Now that Lake Powell has filled, Lake Mead will be used more for regulating than it has in the past and Lake Powell will be used more for storage. This means that the eleva- tion of Lake Mead should fluctuate more throughout the year than it has in the past. It will be high in the spring at the start of the growing season and drop throughout the summer. At the end of the growing season it will start to rise again. It was assumed for these studies that the seasonal variation of Lake Mohave water surface elevations would not deviate much from the normal historical pattern shown in Figure 2. This is because the main purpose of Lake Mohave is to regulate deliveries to downstream water users.
It has been the practice at Hoover Dam to use only the four lcwer intake gates. With the additional 500-MW powerhouse, it will be necessary to use one upper gate in addition to the four lower gates. This gate is on the lowly' Arizona penstock.
C-17 Table 6 ESTIMATED FUTURE RIVER LOSSES AND GAINS-LOWER COLORADO RIVER HOOVER DAM TO THE NORTHERLY INTERNATIONAL BOUNDARY (NIB) Hoover Powerplant Modification Project ' Water Year Unit: 11000 ACRE-FEET 1978 RIVER REACH Actual 1/ 1980 1985 1990 2000 2010 2030
Hoover Dam to Davis Dam Total Reach Loss -305 8 8 8 8 8 8
Davis Dam to Parker Dam Reach Loss 356 386 386 386 386 386 386 Bill Williams Inflow 33 66 66 66 66 66 66 Salvage 2/ 65 65 65 65 65 65 65 c, Total Reach Loss 258 255 255 255 255 255 255 1 -=. " Parker Dam to Imperial Dan Reach Loss 254 206 206 206 206 206 206 Salvage 2/ 58 58 58 58 58 58 58 Total Reach Loss 196 148 148 148 148 148 148
Imperial Dam to NIB Reach tam 147 128 128 128 128 128 128 Salvage 2/ -- 0 0 0 0 0 0 Total Reach Gain 147 128 128 128 128 128 128
Estimate for Unmeasured Return Flows 3/ 200 200 200 200 200 200
Regulatory Was_e to Mexico 4/ 15 15 15 15 15 15
Total Net Loss/or Gain 5/ 2 498 498 498 498 498 498
1/ Losses or ga is calculated by water balance method for each reach. 2/ Service salvage program from Quality of Water, Colorado River Basin, Progress Report No. 9. 3/ Assumes that Current river gains will be assigned as unmeasured return flows from irrigation operations. 4/ Flows required to guarantee 'scheduled deliveries and resulting from inability to regulate floodflows. S/ All loss/gain projections are based on a historical average computed over a different period of years for each rea Table 7 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATES OF ARIZONA AND UTAH ABOVE HOOVER DAM AND HOOVER DAM TO PARKER DAM WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
Unit: 1,000 Acre-Feet (except as noted) 1978 / WATER USER Actual 1 1980 1985 1990 2000 2010 2030
Mogollon Project (Ariz.) 2/ 0 0 0 2 10 10 10 Warner Valley Project 3/ — 10 18 18 18 18 18 Total Above Hoover Dam 10 20 28 28 28 28 Lake Mead National Recreation Area 247 0.5 0.5 0.5 0.5 0.5 0.5 City of Kingman 0 0 0 6 14 18 18 Davis Dam and Government Camp 231 6/ 6/ 6/ 6/ 6/ 6/ 1 Mohave Valley Irrigation - L15 and Drainage District (I&DD) 19,060 18 19 20 21 21 21 Havasu National Wildlife• Refuge 33,760 37.3 37.3 37.3 37.3 37.3 37.3 Fort Mohave Indian Reservation 4/ 20,188 20 59.0 73.7 73.7 73.7 73.7 Lake Havasu I&DD 7,771 8 9.5 11 12 12 12 Central Arizona Project (CAP) 5/ 0 756 7/ 1,470.1 1,417.1 1,419.1 1,419.1 Other Users 0 8/ 8/ — • 8/ ' 8/ 8/ 8/ Hoover Dam to Parker Dam 81,257 81.8 88T.3 1,61$.6 1,575.6 1,581.6 1,581.6
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ The Mogollon Project is an offstream use and therefore is not chargeable to Arizona's mainstream diversion. 3/ The Warner Valley projection is based upon an offstream multipurpose dam and reservoir to provide a full supply to 4,625 acres of new land, a supplemental supply to 9,650 acres, and 16,000 acre-feet of municipal and industrial water supplied to St. George, Utah. 4/ Assumes full development by 1990. 5/ The Central Arizona Project diversions are based upon the assumption that 2.8 MAF per year would normally be available for use by Arizona. 6/ Included in Lake Mead National Recreation Area. 7/ CAP's diversion for water year 1985 is assumed limited to 50 percent of the normal estimated diversion due to aqueduct construction schedule. 8/ Included in Mohave Valley I&DD. Generally averaged calendar year 1964 or date of first diversion if more recent — through 1974. Table 8 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF ARIZONA PARKER DAM TO IMPERIAL DAM WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
UNIT: 1,000 ACRE-FEET (except as noted) 197a 1/ WATER USER Actual — 1980 1985 1990 2000 2010 2030
Town of Parker 856 3/ 3/ 3/ 3/
Colorado River Indian Reservation 2/ 355,570 336.0 378 397 428 428 428
Imperial National Wildlife Refuge 343 3/ 3/ 3/ 3/ 3/ 3/ c) Cibola National Wildlife Refuge 16.8 16.8 16.8 16.8 16.8 16.8 Ivi c) Other Users 32,145 40.0 40.0 40.0 40.0 40.0 40.0
Arizona Totals Parker Dam to Imperial Dam 388,914 392.8 434.8 453.8 484.8 484.8 484.8
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964 by the Bureau, LC Region. 2/ Assumes full development in 2000, on 99,375 acres. I/ Included in other users. Table 9 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF ARIZONA IMPERIAL DAM TO NORTHERLY INTERNATIONAL BOUNDARY AND BELOW NIB WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
UNIT: 1 1 000 ACRE-FEET (except as note 1978 1/ WATER USER Actual - 1980 1985 1990 2000 2010 2030 Yuma Proving round 14 5/ 5/ 5/ 5/ 5/ 5/ North Gila Valley Irrigation District 41,231 4g.8 4g.8 4.8 4.8 4.8 4g. Warren Act Contractors 59 1.1 1.1 1.1 1.1 1.1 1.1 Wellton-Mohawk Irrigation and Drainage District (I&DD) 256,869 300.0 300.0 300.0 300.0 300.0 300. Yuma ID 2/ 65,524 73.4 73.4 73.4 73.4 73.4 73. Yuma Mesa I&DD 2/ 208,278 241.0 241.0 241.0 241.0 241.0 241. r) Unit "B" I&DD 27 37;584 39.3 39.3 39.3 39.3 39.3 -39. ga Return Flow (S5Ah Gila Valley) 3/ -55;349 -61.8 -61.8 -61.8 -61.8 -61.8 61. • City of Yuma 8;872 11.9 11.9 11.9 11.9 11.9 11. Yuma County Water Users' Association 200,490 193.9 193.9 193.9 193.9 193.9 193. Cocopah Indian Reservation 1,775 1.7 1.7 1.7 1.7 1.7 1. Yuma Mesa Outlet Drain 4/ -32,062 -60.0 -60.0 -60.0 -60.0 -60.0 -60. Other Users 38,445 34.3 34.3 34.3 34.3 34.3 34. Arizona Totals Imperial Dam to NIB 771,730 821.6 821.6 821.6 821.6 821.6 821. Effect of Protective Pumping 0 0 -23 -13 -1 -7 -7 Other Uses Below NIB 13,831 19 19 19 19 19 19 Credit for Unmeasured Return Flows -100 -100 -100 -100 -100 Arizona Totals 1,255,732 1,317.2 2,033.7 2,800 2,800 2,800 2,800
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ Diversions used, return flows are itemizedseparately. I/ Unassigned to districts; includes drainage from Yuma Mesa and South Gila Valley. 4/ Return flows of drainage from Yuma Mesa I&DD, Unit "B" I&DD, Yuma County Water Users' Association, and Cocopah Indian Reservation. 5/ Include in other uses. Table 10 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF CALIFORNIA FROM NEVADA-CALIFORNIA BOUNDARY TO PARKER DAM WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
UNIT: 1,000 ACRE-FEET (except as noted) 1978 / 1 WATER USER Actual 1980 1985 1990 2000 2010 2030
City of Needles 2,134 10.0 10.0 7.0 7.0 7.0 7.0
San Bernardino Co-nty 15 5/ 5/ 5/ 5/ 5/ 5/
Metropolitan Water District 2/ 719,992 763.0 550.0 550.0 550.0 550.0 550.0 13.8 C-) Fort Mohave Indian Reservation 3/ 14,389 13.8 13.8 13.8 13.8 13.8
IN) Fort Chemehuevi Inolan Reservation 4/ 1.0 2.8 4.6 7.6 7.6 7.6
Other Users 2,394 5/ 5/ 5/ 5/ 5/ 5/
California Totals (Nevada-California Boundary to Parker Dam) 738,924 787.8 576.6 575.4 578.4 578.4 578.4
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ Includes Tijuana emergency delivery by contract through August 1978. 'Allotment drops to 550,000 acre-feet when CAP comes online. 3/ Assumes full development by 1980 on 2,300 acres. 4/ Assumes full development by 1990 on 2,000 acres. 5/ Included in Needles total. Table 11 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF CALIFORNIA PARKER DAM TO IMPERIAL DAM WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
UNIT: 1 1 000 ACRE-FEET (except as noted 19781/ WATER USER Actual 1980 1985 1990 2000 2010 2030
Parker Dam and Government Camp 221 4/ 4/ 4/ 4/ 4/ 4/
Colorado River Indian Reservation 2/ 12,627 8.0 9.0 33.0 35.0 35.0 35.0
Palo Verde Irrigation District 3/ 433,826 422.7 422.7 422.7 422.7 422.7 422.7 c) ga City of Blythe 3,063 4.0 4.0 4.0 4.0 4.0 4.0 w East Blythe County Water District 495 4/ 4/ 4/ 4/ 4/ 4/
Other Users 202 4/ 4/ 4/ 4/ 4/ 4/
Total California Parker to Imperial 450,434 434.7 435.7 459.7 461.7 461.7 461.7
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ Assumes full development by 2000 on 8,213 acres. 1/ Palo Verde Diversions is based upon the decree accounting average for calendar years 1968 through 1973. 41 Included in Blythe. Table 12 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF CALIFORNIA IMPERIAL DAM TO NORTHERLY INTERNATIONAL BOUNDARY WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project
Unit: 1,000 ACRE-FEET (except as noted) 1978 WATER USER Actual 1/ 1980 1985 1990 2000 2010 2030
Yuma Project Reservation Division (Indian Unit) 35,580 34.1 34.1 34.1 34.1 34.1 34.1 Yuma Project Reservation Division (Bard Unit)2/ 45;222 45 45 39.6 39.6 39.6 39.6 Reservation Division Return Flow 7/ — -21;025 -20 -20 -20 -20 -20 -20 Imperial Irrigation District 3/ 47 2,760,903 2,952.0 2,952.0 2,956.7 2,951.7 2,951.7 2,951.7 c, Coachella Valley Water District 1/ .500;027 485.4 485.4 485.4 '485.4 485.4 485.4 Imperial and Coachella Return Flow 5/ -18 -18 -18 -18 -18 -18 ' City of Winterhaven 110 6/ 6/ 6/ 6/ 6/ 6/ Other Users 14,832 1g.1 1g.1 14.1 lg.1 1g.1 11.1 California Totals Imperial Dam to Boundary 3,335649 3,497.6 3,497.6 3,496.9 3,491.9 3,491.9 3,491.9 Coachella Canal Lining -132 -132 -132 -132 -132 -132 California Totals 4,525,007 4,588.1 4,377.9 4,400.0 4,400.0 4,400.0 4,400.0
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ Bard Unit reduced to decreed diversion limit after 1985. Indian Unit fully developed on 7;743 acres by year 2000. I/ Based upon the 1968-1973 average of the decree accounting. 4/ Rounded off to provide full 4.4 MAF entitlement to California when CAP comes online. 5/ Unmeasured return flow from the All-American Canal. g/ Included in other uses. 7/ Return flow estimated by drain measurements and adjusted for All-American Canal seepage. Table 13 CONSUMPTIVE USE OF DIVERSIONS FROM MAINSTREAM STATE OF NEVADA ABOVE HOOVER DAM AND HOOVER DAM TO NEVADA - CALIFORNIA BOUNDARY WATER YEAR EXCEPT AS NOTED Hoover Powerplant Modification Project UNIT: 1,000 ACRE-FEET (except as noted) 1978 11 WATER USER Actual 11 1980 1985 1990 2000 2010 2030 Lake Mead National Recreation Area 892 1.1 1.6 2 2 2 2 Basic Management, Inc. (BMI) 2/ 7,554 7.2 8.5 9.5 11.6 13.9 14.3 Las Vegas Valley Water District (LVVWD) 5/ 64,865 44.7 62.9 83.5 118.4 252.1 251.7 Boulder City 3,869 8/ 8/ 8/ 8/ 8/ 8/ City of Henderson 7,886 8/, I/ 8/, I/ 8/, I/ 8/, I/ 8/, I/ 8/, 1/ Las Vegas Wash Return Flow -33,816 Nevada Fish and Game • 5 8/ 8/ 8/ 8/ 8/ 8/ Johns-Manville (Pacific Coast Building Products, Inc) 521 8/ 8/ 8/ 8/ 8/ 8/ Ç City of North Lis Vegas 3/ 6,126 I/ I/ I/ I/ I/ I/ 1 - f`aun Nellis Air Force Base 3/ 2;594 I/ I/ I/ I/ I/ I/ Las Vegas Wash 3/ 4/ I/ I/ I/ I/ I/ I/
Total Above Hoover Dam 60,496 53 73 95 132 268 268 Southern California Edison Company 9,053 _ 15 19 23 23 23 23 Fort Mohave Indian Reservation 6/ 6.0 6.3 6.6 7.3 7.9 8.1 Other Uses 7/ 65 Total Hoover Dam to Nevada - California Boundary 2/ 9,118 21.0 25.3 29.6 30.3 30.9 31.1
Nevada Total 69,614 74.0 98.3 124.6 162.3 298.9 299.1
1/ From the decree accounting, "Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in Arizona v. California," dated March 9, 1964, by the Bureau, LC Region. 2/ The remaining portion of Nevada's 300,000 acre-feet allocation is not assigned to a specific project. A major portion of this water is assumed to be available for the Southern Nevada Water Project. 3/ Included in LVVWD. 4/ Depletion of water resulting from operation of proposed desalting plant on Las Vegas Wash for water quality improvement under Title If. 5/ 1980-2030k projections include estimated credit for return flows in Las Vegas Wash. Assume full development by 1980 on 1.939 acres. 7/ Included in Southern California Edison. Included in BMI. A review of annual generation at Hoover Powerplant indicates that there are two seasons during the year in which there is a heavy demand on the powerplant; first, during the spring months of April and May, resulting from heavy doWnstream spring requirements for irrigation water, and secondly,'during the summer Months of July and August, due to heavy irrigation requirements which coincide with the peak power demand. The demand on'Hoover Powerplant is much smaller during the winter and fall seasons. The power Companies schedule maintenance on their other powerplants during the spring to take advantage of the large irrigation releases. The powerplant is essentially operated on a 5-'clay peaking cycle, with minimal peaks occurring on the weekends as shown in Figure 8.
If additional capacity were installed at Hoover Powerplant, it would likely follow the same pattern, i.e., the plant would be loaded to nameplant capacity or above about 4 or 5'percent of the days during the year. It can be assumed that during the fall and winter season that releases would remain as they have'historically, even if addi- tional generation is added at Hoover Powerplant. During the spring and sunnier season, peak releases would increase corresponding to the increase in installed capacity.
All of the existing generators are being uprated from a plant nameplate capacity of 1,340 MW to an estimated 1,800 MW. This will influence the operations by allowing higher peak discharges for short durations which would result in low discharges experienced for longer durations. The total amount of water released will remain the same; only the timing of its release will change. As sown in Figure 9 the peek discharges. will increase from about 40,000 ft /s to around 49,000 ft Is while the low releases would be lower and for longer durations. The spring season is plotted here because the difference between the current condition ancithe uprated condition is most noticeable during this period.
When the Hoover Modification Project s completed, the peak discharges would increase to about 62,000 ft Is. As in the case of the uprating these peaks would be shorter in duration and the low releases would be ldwer and for longer durations. Also, the total amount of water released would not change, just the timing of its release.
To operate Hoover Powerplant at 1,800 MW (uprating) and 2,300 MW (Hoover Modification), baseload (nightime) and sOme peaking (daytime) energy must be displaced from times of low demands to the times of the highest peak demands. This would be done only when generation in excess of 1,340 MW is needed. Under this assumption, a potential revised weekly load curve was constructed by the BUreaurs Division of Power. For low Lake Mohave levels a minimum flow of 2,000 ft /s (70 MW) was adhered to as best as possible. It should .pe mentioned that, historically, flows have gone well below 2,000 ft Is numerous times during the year. With these assumptiops in mind, Figure 10 shows the potential revised weekly discharge curve for the 500-MW powerplant as C.X.1 I 11.•..1.14 1 18 . U3 3.'42. .. -7.Z CIL..it.21 IFiZ .41 WEEKLY LOAD CURVE
Fi00VER AT 1340 MW SERSON nmo
14C0.0 4 I
1200.0 I\
1030.0 I ( 1
I I
600.0
i
I , 400.0 ;1 I 1 i " i IA ' ..1 \.4
. 230.0
]
0.0 7yrrtrrrn I 4111"11-111 • I il■ Ili V? lllll Irr111•11i TTTTTfTTTTTpTTTTTT I 1 ...... TT1 TITTTTTITTITTTTTITTTTTrilTTTrynIrrmirmrrni 4 , l r. 0.0 2_ r2 72 11 1-).-I n 'I AA rl 25.0 18.0 7 n • • • F:CURS
Figure 8
HOOVER DAM WEEKLY DISCHARGE
M - AT 1340 IAN
- AT 1903 IM
• - Al 2300 lalf 65000
80000 -
55000
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
12 24 36 48 60 72 84 Q8 108 120 132 144 156 168
TIME (HOURS)
Spring Season Uprated (1800 AW) vs. Present (1340 114) Figure 9
HOOVER DAM WEEKLY DISCHARGE
El - AT 1340 1111
0 - AT 1000 LA,
• - AT 2300 AM 65000
60000 -
55000 -
50000 -
45000 -
63 40000 - b 35000 -r
30000 4.
25000 -
20000 -
15000
10000 -T
5000
121 t • 12 24 36 48 72 84 108 120 132 168
TIME (HOLPS)
Spring Season Modified (2300 AU) vs. Present (1340 AW) Figure 10 III
I compared to present day operation during the spring season. The summer discharge is plotted'on Figure 11. The dashed curve shows the revised operation and the solid curve shows actual operation. The monthly energy totals will remain the same.
In 1987, the power contracts with the Hoover operating agents will expire. At that time one or both of the operating agents may renew their contracts or the Bureau may take over the operation of the dam. The actual operation of the river-reservoir system will not be affected.
3. Lake Mohave Operation Study. The purpose of this study is to determine whether the future operation scenario used in the development of the power benefit 'analysis done for the Hoover Powerplant Modification Feasibility Report is hydrologically feasible.
The Power Division of the Lower Colorado Region project the future annual energy generation at Hoover Powerplant on an hourly basis for three different scenarios:
--Typical future high energy generation year. --Typical future average energy generation year. --Typical future low energy generation year.
These projections were based on the results of the October 1979 base run of the Colorado River Storage Project (CRSP) Model and the historical energy pattern of calendar year 1978.
Appended Tables A-1 through A-4 show the CRSP results that were used to select and supply data for the three future projections. The average of all the annual energy values in trace No. 2 (4,164 MkWh) on Table A-4 was the closest of the 15 trace averages, to the average of the 15 trace averages (4,124 MkWh). Therefore, trace No. 2 was chosen as the average trace. From this trace the energy generated during the highest year, 1986, the average year, 1996, and the lowest year, 2033, were chosen to represent the three scenarios as shown in the following tabulation:
Projected Hoover Energy Generation (MkWh)
Scenario Year WY-Energy CY-Energy
High Energy Year 1986 8,387 7,680 Average Energy Year 1996 4,184 4,204 Low Energy Year 2033 3;050 3;052 (Base Pattern Year) 1978 3,540 The energies in Table A-4 are for a water year (WY), but the hourly energy data available for 1978 were from a calendar Year (CY). Therfore, the CY energy values for 1986, 1996, and 2033 were computed
C-27 as shown previously. Appended Table A-6 through A-8 are the monthly energies projected by the CRSP model from which the CV energies were obtained. The historical energy pattern for CV 1978 was obtained by the Power Division from hourly energy values off a "strip chart" from a meter on the generators. Using this pattern and the CRSP projected monthly energy data, the Power'Divisien projected the hourly energy generation for CV 1986, CV 1996, and CV 2033;The reason CV 1978 was chosen as a base pattern was mainly for convenience; no other year had hourly energy data stored on a computed memory device. Also, CV 1978 was not an ususual year--Its annual energy production was about halfway between the future "low" year and the future "average" year.
The average yearly energy projection for the modified Hoover Powerplant was such that the alternative powerplant used in the power benefit analysis could be operated at an annual plant factor of 8.75 percent. The high year was not analyzed, but it would have a plant factor of at least 8.75 percent. To be conservative, the Power Division chose 7.5 percent for the average annual plant factor to be used in the analysis. An important assumption used in the energy projections was that all of the power produced could be utilized.
The power benefit analysis would be hydrologically feasible if the following conditions could be met given the projected operating criteria used in the power benefit analysis.
a. The downstream water demands are satisfied.
b. The elevation of the surface of Lake Mohave does not go beyond the historic limits of 647.0 and 630.5 feet above mean sea level.
c. The Hoover energy production is such that the alternative powerplant used in the power benefit analysis could be operated with an annual plant factor of 7.5 percent.
The Water Scheduling Branch modified a daily operations model to handle a year of data. *The model was calibrated *using historic CV 1978 data. First, reach losses and gains for CV 1978 were computed using daily discharges from Hoover Dim that were computed from the hourly energy data Provided by the Power Division, 'recorded daily discharges from Davii Dam, and recorded Lake Mohave elevations. Then as a check, the computed 'gains and losses were used to compute Lake Mohave elevations ihown on appended Table A-15. These 'computed elevations compared well with the historic elevations. The reach gains and losses included evanoration, odnk storage, and local inflow.
The model was then used to test the three scenarios for the modified Hoover Powerplant. Hoover daily discharges were computed from the project energy data for the three scenarios. The monthly totals of these daily discharges matched the monthly discharge
C-28 HOOVER DAM WEEKLY DISCHARGE
• - AT 1310 WM
o - AT WOO MN
• - AT-2.100 65000,
60000 -
55000 -
50000 -
45000 -
40000 -
35000 -T
30000 -
25000 -
20000 -
15000 -
10000 'T
5000
I • • 12 24 48 60 72 04 96 108 120 132 144 150 166
TR& ( -10■RS)
Summer Season Modified (2300 9U) vs. Present (1340 9W) Figure 11 projected by CRSP shown on appended Tables A-10, A-12, and A-14. Davis Dam discharges were projected using the CY 1978 historic pattern and the projected CRSP monthly releases shown on appended Tables A-9, A-11, and A-13. Long-term average reach losses and gains were used instead of 1978 reach losses and gains.
The studies consider high, low, and average future water supply. years on a daily basis. ResultS of the October 1979 long-range monthly simulation using the CRSP model were selected for the study's projected water supply conditions. Anticipated hourly project condition Hoover energy generation patterns for 1-year durations were formulated by the Lower Colorado Region, Division of Power by means of a simulated release analysis of average hydroelectric power patterns.
The subject daily water budget operation studies use those derived hourly energy values and a correlated energy equation to compute the necessary quantities of daily releases required at Hoover Powerplant to generate the energy amounts. The anticipated Davis Powerplant daily releases used were the average monthly release quantities determined in the CRSP study.
The operations program takes into consideration the following factors:
1. Releases from Glen Canyon Dam, from CRSP studies, with daily values derived using the 1978 pattern.
2. Lake Mead end of month elevations resulting from long-range simulation runs. Gains for the Glen Canyon to Hoover reach reflect evaporation, bank storage, southern Nevada pumping, and other gains and losses.
3. Loss-gains in the Hoover to Davis reach as projected in the long-range simluations, redistributed daily.
4. Monthly releases from Davis Dam as determined in long-range operations for projected downstream water requirements, surplus and/or shrotage conditioni, and flood control regulation.
5. Static head and gross energy, area-capacity tables for Lakes Mead and Mohave (extended for purposes of these studies), and alogrithms at Hoover' and Davis Powerplants. Davis Powerplant generation exceeds maximum energy and generator capacity especially in the high year run.
An hourly operations model was run from May 9-31, 2033 (low year) in order to seP if it would be necessary to analyze all three scenario, on an nourly basis. This hourly model computed elevationl of Lake Mohave that did not vary significantly within any of the 24-hour periods. There was, therefore, no need to analyze the scenarios on an hourly basis.
a. Study Results. The daily operations model was first calibrated using historic provisional 1978 data. The energy equations
C-29 for Hoover Powerplant used in the model were verified by operating the program with 1978 energy generation values and comparing the computed results with the measured reservoir elevations; static head, and releases. Appended Table A-15 compares the results of the daily opera- tion study Program using observed 1978 data (Form 04-351) with those using historic hourly generation values supplied by the Division of Power. Examination of the data shown suggests that the reason Lake Mohave's computed 1978 daily elevations differ from those in the daily historic operation model is largely because of differences between the respective powergeneration valOes. It is concluded that the program is 'capable of predicting future daily Lake Mohave elevations to within ±0.5 foot.
Operation studies (daily basis) were then made under conditions wherein total monthly quantities of water released at Hoover correspond to projected high; low, and average hydroelectric power conditions. Those results were computed to the earlier inde- pendent monthly CRSP study projections. Due to the nature of the results of the daily studies, no hourly studies were attempted.
Appended Figure A-1 illustrates the projected effects of modified Hoover Powerplant releases upon Lake Mohave elevations under the three future study conditions as compared to the observed 1978 condition.
Tables A-16, A-17, and A-18 (appended) summarize on a monthly basis the results of the three future condition daily opera- tion studies and compare those results with monthly CRSP projections.
b. Study Evaluation and Conclusions. The subject studies were basically formulated to meet only projected Hoover hydroelectric power patterns in conjunction with the project CRSP model releases at Davis Dam. No "operation" of Lake Mohave was programmed because one of the study's primary objectives was to assess the comparative effects of the projected hydroelectric power patterns upon Lake Mohave under the various specific water supply conditions.
The operation studies indicate that fluctuations in Lake Mohave levels would result under each of the three projected conditions. The Hoover releases necessary to generate the projected daily Hoover hydroelectric power patterns could in most of the low, average, and high release conditions be stored in Lake Mohave with the level Of Lake Mohave being expected to fluctuate as shown by the studies. It should be pointed out that Lake Mohave levels are norr.....ly scheduled no lower than 630.5 feet in order to allow naviga- tion in the marina areas and to avoid potential damage to recreational facilities and to watercraft. In order to prevent Lake Mohave from
C-30 rising above elevation 647.0, lake levels are normally scheduled no higher than 645.0. This normally provides adequate regulatory space for reduced releases for downstream water uses and for storm inflbws. It is seen that under average and high water supply conditions Lake Mohave's daily level rose to within a foot of the spillway's crest (elevation 647.0) during the April-May period.
Under actual project conditions, however, the daily discharge pattern from Davis Dam would to some extent be coordinated with Hoover and Parker Dams to "smooth" fluctuations caused by releases from Hoover Dam. There are, however, definite limits to such daily modification of Davis releases. Downstream requirements for irrigation and other purposes within the United States, and delivery of water to Mexico will normally establish the daily water releases that must be made from Lake Mohave since Lake Havasu has no appreci- able regulatory storage capacity. To assure stability of the embankment and Davis Dam operating facilities, Lake Mohave drawdown rates should not exceed one foot per day (average) for 10 days nor a total of 15 feet in 30 days.
Minimum average releases for flood control purposes are specified by U.S. Army Corps of Engineers regulations. Hoover releases may only be less than the specified amounts for part of the flood release period, provided that the average releases for the entire period wi'y equal the mandated release and that flows do not exceed 40,000 ft Is at the Colorado River below Davis Dam. Prior approval of release deviations is required from the District Engineer, Los Angeles District, Corps of Engineers, except for emergencies and certain unplanned minor deviations primarily construction or maintenance oriented.
Daily Lake Mohave levels are shown to drop to lows of approximately 630.0 feet during August or September of each of the three annual water supply conditions operated.
It is concluded that under the guidelines used for the study, the modeling results indicate a potential capability for the system to support the projected daily hydroelectric power patterns at a modified HOOver Powerplant.
C-31 ■ . III. TAILWATER STUDIES
A. Introduction
Higher discharges from the powerplant would be necessary to generate the additional capacity that the Hoover Powerplant Modification Project would provide. This would result in higher tailwater surface elevations,. higher velocities, and increased degra- dation. The purpose of theie studies is to quantify the downstream effects resulting from the higher discharges.
B. Design Discharges
The discharges that would result from the modification need to be determined, in order to analyze the downstream effects. A weekly load curve was produced by the Bureau's Division of Power from historical data recorded in CV 1978. This was used to project weekly load curves for future conditions. These weekly load curves, like Figure 8, were converted into the weekly discharge hydrographs shown in Figures 3 through 7 and 10 and 11. These hydrographs are the same shape as the weekly load curves. The present condition for each season is illus- trated in Figures 3 through 7.
The conversion of power values to discharge values was accom- plished with a computer program named QPOWER. The basic computa- tional procedure is:.
1. Using Lake Mead and Lake Mohave elevations a starting head is computed.
2. Using this head and the first hourly power value of the week, a discharge value is computed.
3. Using this discharge value and the elevation of Lake Mohave, a tailbay elevation is read off the tailwater curves shown in Figure 12 lond used to compute another head value. For releases above 40,000 ft Is the curves were extended using a straight line extrap- olation.
4. This head is compared to the initial head computed back in step 1.
a. If the two heads are not equal another head is inter- polated. Using this new head and the *same power value, another discharge value is computed. This value is used to read another tailbay elevation off the tailwater curves and a corresponding head is computed. If this value is not equal to the previous head then this iterative process continues until they do match..
b. When the two heads match then the next hourly power value is read and the procedure is repeated until the whole weekly load curve has been converted to discharge values.
C-32 The equation used to convert power values to discharge values is:
Q = 13,111 P/H (1) where, Q = discharge (ft3/s) P = power (MW) H = head (ft).
Ihe constopt, 13,111, was obtained from the basic hydroelectric power equation±',
Q = 11,800 P/H (2) in which the turbine-generator efficiency is assumed to be 100 per- cent. When uprated, the Hoover turbine and generators should operate at around 90 percent efficiency which results in a constant of 13,111. Lake Mohave elevation was set at 647 feet and Lake Mead was set at 1140 feet to have a rated head of near 490 feet.
Ihe peak discharge for the 500-MW alternative, on Iable 14, was computed using this methodology and was used to analyze this alternative in the water surface profiles study. Ear all the other alternatives besides the "Present Condition" a rated head of 490 feet and an efficiency at 90 percent was assumed. So, they were computed with the following formula:
13,1112 490. (3)
Ihis method was used on these alternatives because the 500-MW powerplant alternative was so highly favored that less .accuracy was required 1 for these alternatives. Eor the present condition 40,000 ft /s were used because it was the highest recorded steady state discharge.
1/ Ibid 1, page 302.
C-33 "7
5
47 -
46-
NOTE operatin4 FIGURE 12 -- _Gurveß shawn_11MkailLacejlosed_on_daily fairly well supported: for Hoover.: . data and are - - power releases between 10,000 and 25,000:c.f.S. HOOVER POWER PLANT TAILVtlATER CURVE - . July 30,1954 45-300-59
4f 40 34 35 36 37 38 39 28 29 30 31 32 33 23 2.4 2.5 . 26 27 • 6 1 7 18 1 9 20 21 22 40 to II 12 1 3 1 4 1 5 1 5 __NOOVER RELEASE _IliCILISANDS--bF
_ _ - Table 14 PEAK DISCHARGES Hoover Powerplant Modification Project
Alternative Peak Discharge (ft3/s)
500-MW Powerhouse 62,000 Replacement of A8 and A9 56,000 Pumped Back Storage) 76;000 Uprated Conditio n 49,0001, Present Condition- 40,000-
C. Water Surface Profiles
1. Cross Sections. Forty cross sections of the Colorado River channel were measured, during the spring of 1977, starting at the downstream end of the Nevada powerhouse deck and ending 13.5 miles downstream. It was assumed that lake conditions predominate at mile 13.5, and therefore, the water surface elevation measured at Davis Dam would be the same as at mile 13.5. The survey party started by using a sounding machine, but found the results erroneous when checked against a measuring tape. So divers using altimeters measured the depth. The horizontal distance was measured with a weighted line which was laid along the bottom of the channel. The line was divided into 5-foot intervals. No corrections for the slope were made so that the distance recorded was not horizontal but along a slope. Also, no corrections were made for the sag in the line caused by the current. Geologist divers recorded comments about each cross section as shown in Figure 13 (22 cross sections).
The assumption that the elevation measured at Davis Dam and the elevation at mile 13.5 would be the same, was questionable, since the interface between the river and Lake Mohave is usually located between 14 and 20 miles below the dam and because Mohave is such a narrow, river-like lake, possibly having a significant hydraulic slope.
1/ This is the future "without project" or "do nothing" alternative. The powerplant is currently being uprated as an operation and maintenance activity. 2/ The "present condition" is not an alternative since the units are being uprated. The "do nothing" alternative would be the "uprated condition." 3/ The momentary peak recorded discharge was 40,600 ft Is. This occurred August 10, 1978, during the Hoover Modification unsteady f19w test releases. The maximug steady flow release was 40,000 ft Is and that is why 40,000 ft Is was used for the present condition peak discharge.
C-34
Therefore, 50 additional cross sections were read off topographic maps. These sections started at 13.87 miles below Hoover and ended at Davis Dam, 64.38 miles below Hoover. So for the first 13.5 miles an average of three cross sections per mile was taken and for the remain- ing 51 miles an average of one cross section per mile. Significant hydraulic slopes were calculated down to mile 20 using these data.
The first 40 cross sections are listed with their corresponding miles below Hoover Dam in Table 15. Figure 14 shows where these sections are located along the river.
Three different water surface profile studies were performed before the computed profiles matched the recorded profiles with sufficient accuracy. 'Then, profiles for the Hoover Modification Project condition were computed.
2. Steady Flow Tailwater Study. 1/The Engineering and Research (E&R) Center did a tailwater study— using the first 40 cross Sections, in the fall of 1977. The steady flow computer program named "PSEUDO" was used in this study. 7 model was calibrated by adjust- ing the roughness coefficient,= Manning's "n", to produce water surface elevations matching those recorded at the Hoover tailbay and U.S. Geological Survey (USGS) gaging station around 0.7 mile down- stream of Hoover Dam. Table 16 shows the results of this study. A roughness coefficient of 0.045 provided the closest fit. The average difference between the calculated tailbay elevation and the measured tailbay elevation was 0.5 foot. This difference is 2.5 times the error incurred in measurement which is 0.2 foot. When compared to the USGS gage below Hoover Dam, the average difference was 0.9 foot. It was concluded that these results were not sensitive enough to be used for projecting what the effects of the modification would 'be.
3. Calibration of Unsteady Flow Model. In order to improve the quality of the computed values throughout the reach, the following !flan was carried ()qt. Five continuous water level recorders were installed throughout the reach in addition to the existing USGS gage 0.7 mile below Hoover. Also, 21 crest stage gages were installed thoughout the first 14.2 miles of the river as shown in Figure 15. The continuous water level recorders are labeled G-1, G-2, ..., G-6 and the crest stage gages are labeled CS-1 1 CS-2, ..., CS-21. Arrangements were made With the Hoover operating agents to follow a special 5-day test relgase schedule as plotted on Figure 16. Minimum discharge was 2,000 ft Is and the peak 'releases for the first 3 days, August 6-8, 1978, were held constant for 6 hours in order to create steady flow conditions throughout the reach. On August 9-10, 1978, the releases were not held constant but varied to produce un- steady flow conditions which more closely represent actual flow conditions. Discharge was being measured by acoustical flow fil ters on each penstock.
1/ Ibid 2. 2/ The roughness coefficient was constant throughout the reach.
C-35 Table 15 COLORADO RIVER CROSS SECTIONS Hoover Powerplant Modification Project
Cross Section Miles below No. Hoover Dam
0 0.000 1 0.156 2 0.330 3 0.484 4 0.647 5 0.908 6 1.209 7 1.588 8 1.947 9 2.371 10 2.751 11 3.139 G-2-1/ 3.411 12 3.600 13 4.018 14 4.480 15 4.884 16 5.254 17 / 5.683 G-3-1 5.831 18 6.093 19 5 6.526 20 6.864 21 7.171 22 7.587 23 7.994 24 8.341 25 8.667 26 9.064 27 1/ 9.398 28 G-4- 9.788 29 10.144 30 10.532 31 10.911 32 11.366 33 11.751 34 12.109 35 1/ 12.806 G-5- 12.970 36 13.531
1/ Numbers of continuous water level recording gages.
C-36 •• • nu. .6••••••
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