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Stetson Creek Diversion and Cooper Lake Dam Facilities Project Supporting Design Report - Jun 2012 - REF Grant 7040005
STETSON CREEK DIVERSION AND COOPER LAKE DAM FACILITIES SUPPORTING DESIGN REPORT FINAL REPORT JUNE 14, 2012 Prepared by: STETSON CREEK DIVERSION AND COOPER LAKE DAM FACILITIES SUPPORTING DESIGN REPORT FINAL REPORT JUNE 14, 2012 Prepared by: Stetson Creek Diversion and Cooper Lake Dam Facilities Page i Supporting Design Report – FINAL 14 June 2012 TABLE OF CONTENTS ACRONYMS AND ABBREVIATIONS.................................................................................... iv DISCLAIMER.............................................................................................................................. vi COPYRIGHT............................................................................................................................... vi EXECUTIVE SUMMARY ....................................................................................................ES-1 1.0 INTRODUCTION.............................................................................................................1-1 1.1 Background................................................................................................................1-1 1.2 Existing Project Layout..............................................................................................1-1 1.3 Proposed Modifications.............................................................................................1-2 2.0 GENERAL DESIGN CRITERIA ...................................................................................2-1 2.1 Design Criteria and Project Facts ..............................................................................2-1 2.2 Assumptions...............................................................................................................2-3 2.3 Governing Codes and Standards................................................................................2-3 2.3.1 Civil and Structural Engineering ...................................................................2-4 2.3.2 Geotechnical Engineering..............................................................................2-6 2.3.3 Mechanical Engineering................................................................................2-6 2.3.4 Electrical Engineering....................................................................................2-6 2.4 General Structural Criteria.........................................................................................2-6 2.4.1 Material Properties.........................................................................................2-6 2.4.2 Structural Loads.............................................................................................2-7 3.0 FEATURE-SPECIFIC DESIGN CRITERIA................................................................3-1 3.1 Cooper Lake Dam Access Road................................................................................3-1 3.1.1 Feature Description........................................................................................3-1 3.1.2 Design Criteria and Assumptions..................................................................3-1 3.1.2.1 Chugach Responsibilities................................................................3-1 3.1.2.2 Contractor Responsibilities.............................................................3-1 3.2 Diversion Dam and Diversion Intake Structure.........................................................3-2 3.2.1 Feature Description........................................................................................3-2 3.2.2 Design Information........................................................................................3-3 3.2.2.1 Hydrology.......................................................................................3-3 3.2.2.2 Hydraulics.......................................................................................3-4 3.2.2.3 Geotechnical Design.......................................................................3-6 3.2.2.4 Stability Design...............................................................................3-9 3.2.2.5 Structural Design ..........................................................................3-10 3.2.2.6 Flow Control and Monitoring.......................................................3-10 3.2.3 Access..........................................................................................................3-11 3.2.4 Construction.................................................................................................3-11 3.2.5 Maintenance.................................................................................................3-11 3.3 Diversion Pipeline and Construction Access...........................................................3-12 3.3.1 Feature Description......................................................................................3-12 Stetson Creek Diversion and Cooper Lake Dam Facilities Page ii Supporting Design Report – FINAL 14 June 2012 3.3.2 Design Information......................................................................................3-12 3.3.2.1 Pipeline Routing............................................................................3-12 3.3.2.2 Pipeline Materials.........................................................................3-12 3.3.2.3 Pipeline Hydraulics.......................................................................3-12 3.3.2.4 Geotechnical Design.....................................................................3-13 3.3.2.5 Structural Design ..........................................................................3-13 3.3.3 Pipeline Bench / Pipeline Construction Access...........................................3-14 3.3.4 Construction.................................................................................................3-15 3.3.5 Maintenance.................................................................................................3-15 3.4 Diversion Outfall .....................................................................................................3-16 3.4.1 Feature Description......................................................................................3-16 3.4.2 Design Information......................................................................................3-16 3.4.2.1 Hydraulics and Siting....................................................................3-16 3.4.2.2 Flow Diffusion..............................................................................3-16 3.4.2.3 Geotechnical Design.....................................................................3-16 3.4.2.4 Structural Design ..........................................................................3-17 3.4.3 Construction.................................................................................................3-17 3.4.4 Maintenance.................................................................................................3-17 3.5 Siphon Outlet Works................................................................................................3-17 3.5.1 Feature Description......................................................................................3-17 3.5.2 Design Information......................................................................................3-18 3.5.2.1 Hydrology and Hydraulics............................................................3-18 3.5.2.2 Geotechnical Design.....................................................................3-22 3.5.2.3 Structural Design ..........................................................................3-23 3.5.3 Construction.................................................................................................3-24 3.5.4 Maintenance.................................................................................................3-25 3.6 Instrumentation........................................................................................................3-25 3.6.1 Feature Description......................................................................................3-25 3.6.2 Design Information......................................................................................3-26 3.7 Borrow Areas...........................................................................................................3-28 3.7.1 Feature Description......................................................................................3-28 3.7.2 Design Information......................................................................................3-29 Stetson Creek Diversion and Cooper Lake Dam Facilities Page iii Supporting Design Report – FINAL 14 June 2012 LIST OF APPENDICES Appendix A – FERC Order on Offer of Settlement and Issuing New License Appendix B – Calculations B1 Hydraulics B2 Diversion Dam Bearing Capacity B3 Diversion Dam Abutment Stability B4 Diversion Dam and Intake – Structural B5 Diversion Dam – Adverse Rock Joint Sliding B6 Division Access Rock Cut – Kinematic Analysis B7 Spiral Nail Reinforced Slopes B8 Gabion Walls B9 Diversion Pipeline Buckling B10 Diversion Pipeline Miscellaneous Calculations B11 Diversion Pipeline Culvert Sizing B12 Diversion Pipeline Collar Weight B13 Diversion Outlet Structures – Bearing Capacity B14 Riprap Sizing and Filter B15 Siphon Outlet – Structural B16 Siphon Outlet Pipe Calculations B17 Siphon Cutoff Wall – Structural B18 Solar Panel Supports Stetson Creek Diversion and Cooper Lake Dam Facilities Page iv Supporting Design Report – FINAL 14 June 2012 ACRONYMS AND ABBREVIATIONS % percent AASHTO American Association of State Highway and Transportation Officials ac-ft acre-feet ACI American Concrete Institute AISC American Institute of Steel Construction AISI American Iron and Steel Institute ANSI American National Standards Institute ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASR Alkali-Silica Reaction ASTM ASTM International AWS American Wielding Society AWWA American Water Works Association cfs cubic feet per second Chugach Chugach Electric Association, Inc. EL elevation FERC Federal Energy Regulatory Commission fps feet per second H horizontal HDPE high-density polyethylene IC instrumentation and controls ICC International Code Council ID inside diameter kV kilovolt MIF minimum instream flow MWH MWH Americas, Inc. MWh megawatt hours NACE NACE International NEC National Electric Code NEMA National Electric Manufacturers Association NESC National Electrical Safety Code NETA National Electric Testing Association NFPA National Fire Protection Association OPCC Opinion of Probable Construction Cost PME Potential Cooper Creek Protection, Mitigation and Enhancement Measures Project Stetson Creek Diversion and Cooper Lake Dam Facilities Project pcf pounds per cubic foot PLC programmable logic controller PTI Post-Tensioning Institute psf pounds per square foot psi pounds per square inch PV Photo voltaic RTU remote terminal unit SCADA supervisory control and data acquisition Stetson Creek Diversion and Cooper Lake Dam Facilities Page v Supporting Design Report – FINAL 14 June 2012 ACRONYMS AND ABBREVIATIONS (CONTINUED) SDR Supporting Design Report Siphon Outlet Spillway Siphon Outlet Facility SSPC The Society for Protective Coatings Siphon Option Spillway Siphon Outlet Facility Option UHF ultra-high frequency USACOE U.S. Army Corps of Engineers USBR U.S. Bureau of Reclamation USGS U.S. Geologic Survey V Vertical W Watt(s) yd Yard(s) VDC volts direct current WSEL water surface elevation Stetson Creek Diversion and Cooper Lake Dam Facilities Page vi Supporting Design Report – FINAL 14 June 2012 DISCLAIMER This report has been prepared in accordance with the terms set out in the contract between Chugach Electric Association, Inc. (Chugach) and MWH Americas, Inc. (MWH). Some of the information, evaluations, and opinions contained herein were based on data and results prepared by or obtained from other parties not under the direct control of MWH. In preparing this report, MWH made use of, and relied upon, data, drawings, analyses, reports, memos, letters, e-mails, and other information provided by others. While MWH did not perform independent investigations or analyses to determine the validity or suitability of such items and information, MWH did comply with applicable industry standards in MWH’s: (i) evaluation and use of any third party data, drawings, analyses, reports, memos, letters, emails, and other information, and (ii) the generation of the information, evaluations and opinions contained herein. Therefore, neither MWH nor Chugach or any person acting on their behalf, may make any warranty, expressed or implied, or assume any liability with respect to the use of any information, method, product, process, or statement contained in this report. Any recipient of this report, including Chugach, or any others, by their receipt and use of this report, hereby releases MWH and Chugach from any liability for direct, indirect, or consequential loss or damage, whether arising in contract, tort (including negligence, but excluding gross negligence), strict liability, or otherwise. MWH was neither requested to perform nor has performed environmental or regulatory investigations or assessments in connection with the facilities described in this report. Also, MWH was neither requested to, nor has performed, any economic analyses or detailed evaluation of any permits or licenses. The content of this report is governed by confidentiality clauses in the contract between MWH and the Client. The contents of this document may not be disclosed to other parties in a manner not consistent with the terms of the confidentiality clauses of the contract. COPYRIGHT © 2012 Chugach Electric Association, Inc., Anchorage, Alaska. All rights reserved under U.S. and foreign law, treaties and conventions. The attached work was specifically ordered under an agreement with Chugach Electric Association, Inc., Anchorage, Alaska. All rights in the various work produced for or under this agreement, including but not limited to study plans and study results, drafts, charts, graphs and other forms of presentation, summaries and final work products, are the exclusive property of Chugach Electric Association, Inc. Stetson Creek Diversion and Cooper Lake Dam Facilities Page vii Supporting Design Report – FINAL 14 June 2012 PROJECT TEAM The following individuals were the key personnel involved in the preparation of the Stetson Creek Diversion and Cooper Lake Dam Final Supporting Design Report: Trey Acteson – Chugach Project Manager Peter Poray – Chugach Project Engineer Brian Miskill – MWH Project Manager Heather Williams – MWH Assistant Project Manager Dave Thompson – MWH Lead Civil Engineer Matt Prociv – MWH Civil Engineer Paul Richards – MWH Senior Geotechnical Engineer Wade Moore – MWH Senior Hydraulic Engineer Jeff Coleman – MWH Supervising Engineer Aaron Orr – MWH Mechanical Engineer Steve Baughn – MWH Senior Electrical Engineer Stetson Creek Diversion and Cooper Lake Dam Facilities Page ES-1 Supporting Design Report – FINAL 14 June 2012 EXECUTIVE SUMMARY Chugach Electric Association, Inc. (Chugach) assessed the feasibility of various Stetson Creek Diversion and Cooper Lake Dam Outlet Facilities Project (Project) as part of the requirements listed in Federal Energy Regulatory Commission’s “Order on Offer of Settlement and Issuing New License” (Settlement Agreement) issued on August 24, 2007. The goal of the Project is to improve fish habitat in Cooper Creek by diverting cold water from Stetson Creek, a tributary of Cooper Creek, to Cooper Lake and releasing warmer surface water from Cooper Lake into Cooper Creek. Several options to meet the goal of providing warmer water to Cooper Creek were examined in the August 2004 “Potential Cooper Creek Protection, Mitigation and Enhancement Measures” (PME) Report developed by MWH for Chugach and one option became the basis of the Settlement Agreement requirements. Based on the results of that report, Chugach asked MWH to assess the feasibility of the selected option – a diversion dam and pipeline from Stetson Creek, and outlet works at Cooper Lake Dam. Various diversion configurations were evaluated and documented by MWH in 2009 and 2010. Chugach selected the Siphon Option alternative, with outlet facilities in the existing Cooper Lake Dam spillway alignment, for Final Design. This Supporting Design Report (SDR) describes final project layouts and features designed as part of the Project and standards and criteria used during the design of the Project. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 1-1 Supporting Design Report – FINAL 14 June 2012 1.0 INTRODUCTION 1.1 BACKGROUND As part of the requirements listed in the Federal Energy Regulatory Commission (FERC) “Order on Offer of Settlement and Issuing New License” (Settlement Agreement) issued on August 24, 2007 (as contained in Appendix A), Chugach Electric Association, Inc. (Chugach) assessed the feasibility of the proposed Stetson Creek Diversion and Cooper Lake Dam Facilities Project (Project). The Project will be located at the northern extent of the existing Cooper Lake Project, approximately 4.5 miles south of Cooper Landing, Alaska. The overall purpose of the Project is to divert flow from Stetson Creek to Cooper Lake, and release warmer surface water from Cooper Lake to Cooper Creek to enhance salmon spawning habitat. Chugach contracted MWH to conduct feasibility studies for various Project alternatives. Those studies are documented in previous MWH reports. Chugach contracted MWH to proceed with Final Design of the Siphon Option alternative for the Project. This Supporting Design Report (SDR) documents assumptions and engineering design parameters specific to the Siphon Option, as described in MWH’s Final Feasibility Report, dated March 14, 2011. This SDR also documents standards and criteria used during final design of the Project,, and includes calculations and technical information in accordance with 18 CFR 4.41. 1.2 EXISTING PROJECT LAYOUT The existing Cooper Lake Project consists of: A 920-foot-long, rock-and-fill dam that raises the elevation of Cooper Lake (a natural lake) to a licensed maximum operating level of 1,210 feet mean sea level. Cooper Lake, with a surface area of 2,910 acres. An intake structure on the east shore of Cooper Lake; a 10,686-foot-long tunnel and penstock. A powerhouse located on the southwest shore of Kenai Lake containing two turbine- generators, each rated at 9.69 MW. A 6.3-mile-long, 69-kilovolt (kV) transmission line extending from the powerhouse to the Quartz Creek substation. A step-up transformer at the Quartz Creek substation. A 90.4-mile-long, 115-kV transmission line from the Quartz Creek substation to the Anchorage substation. Operations currently divert all flow from Cooper Lake through the tunnel/penstock to the powerhouse, where it is discharged into Kenai Lake. The 4.8-mile-long Cooper Creek bypassed reach below the Cooper Lake dam receives no flow from Cooper Lake; there is no existing minimum flow requirement for Cooper Creek and no outlet structure to provide such flows. The project has an average annual generation of about 48,500 megawatt-hours (MWh) and an average outflow through the powerhouse of about 100 cubic feet per second (cfs), which is equivalent to 73,000 acre-feet/year. Powerhouse discharge ranges from 0 to 380 cfs into Kenai Lake, which is the source of the Kenai River. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 1-2 Supporting Design Report – FINAL 14 June 2012 1.3 PROPOSED MODIFICATIONS The Project alternative that has been selected to undergo Final Design is the Siphon Option, which includes the following main elements: Construction of a new Diversion Dam on Stetson Creek, Construction of a 2.2-mile-long diversion pipeline from the new Diversion Dam on Stetson Creek to Cooper Lake, and Construction of Siphon Outlet Facilities in the existing Cooper Lake Dam spillway alignment to allow controlled releases of water from Cooper Lake into Cooper Creek. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-1 Supporting Design Report – FINAL 14 June 2012 2.0 GENERAL DESIGN CRITERIA The design criteria for the Project are based on Chugach’s Settlement Agreement filed August 24, 2007 (Appendix A), with FERC for the Cooper Lake Hydroelectric Project No. 2170. Items not specifically identified in the Settlement Agreement are defined as assumptions. The assumptions are based on conversations with Chugach personnel and engineering judgment, as informed by available hydraulic, hydrologic, geotechnical, operations, and other data. 2.1 DESIGN CRITERIA AND PROJECT FACTS Cooper Lake Dam: Top of Dam elevation (EL) – 1,220 feet Top of Dam Core EL – 1,215 feet Spillway Invert EL – 1,207 feet (nominal) Spillway Weir Crest EL – 1,210 feet Dam Length – 920 feet Spillway Length – 800 feet Cooper Lake Water Surface Elevations (WSEL): Normal Cooper Lake operating range – 1,194 to 1,160 feet Average Yearly Cooper Lake WSEL fluctuation – 15 feet+/- Average Monthly Cooper Lake WSEL fluctuation – 1 to 2 feet+/- Average Daily Cooper Lake WSEL fluctuation – 1 inch+/- Maximum Cooper Lake operating WSEL – 1,210 feet Minimum Cooper Lake operating WSEL – 1,160 feet Cooper Lake Storage Volumes: Cooper Lake Storage at WSEL 1,210 feet (spillway weir crest) – 230,000 ac-ft Cooper Lake Storage at WSEL 1,194 feet (FERC-restricted) – 190,000 ac-ft Cooper Lake Volume Available for Generation at WSEL 1,210 feet – 120,000 ac-ft Cooper Lake Volume Available for Generation at WSEL 1,194 feet – 80,000 ac-ft Cooper Lake Refill and Drawdown: Normal Cooper Lake Refill Period – May 1 to Sept 30+/- Normal Cooper Lake Drawdown Period – Oct 1 to Apr 30+/- Stetson Creek Diversion: Maximum Allowable Diversion from Stetson Creek – 110 cubic feet per second (cfs) Minimum Annual Volume Diverted from Stetson Creek to Cooper Lake – 18,285 ac-ft+/- Minimum Instream Flow (MIF) Remaining in Stetson Creek during Diversion – None specified, but to be taken “(if any) from the total amount of water available for release to Cooper Creek” as indicated in the Settlement Agreement. The sluice gate at the Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-2 Supporting Design Report – FINAL 14 June 2012 Diversion Dam is sized to pass 100 cfs at full pool (i.e., water to the crest of the Diversion Dam). MIF in Stetson Creek will be set by Interagency Committee every year by May 31 after construction is complete. Maximum Number of Days of Flushing Flow through Stetson Creek Diversion in a Rolling 10-year period – 30 days Flushing Flow defined as average daily flow at the U.S. Geological Survey (USGS) gage at the mouth of Cooper Creek Flushing Flow is provided only from Stetson Creek Diversion. Stetson Creek Diversion Flow Control – Manual Expected Generation Increase from Stetson Creek Diversion Flow – 8,029 ac-ft Flows through the Stetson Creek Diversion Pipeline shall be monitored by Chugach on, at least, 15-minute intervals. The data collected shall be reported quarterly to the Interagency Committee. Cooper Lake Dam Facilities – Temperature Release: Total Volume Released from Cooper Lake into Cooper Creek per year – 10,256 ac-ft Maximum Instantaneous Cooper Lake Release Flow – 30 cfs (assumed to correspond to summer months requiring a release of 20 to 25 cfs, as indicated below, and a minimum WSEL of 1,170, which is 10 feet above the historical reservoir low level) Flow releases from Cooper Lake to Cooper Creek shall be monitored by Chugach on, at least, 15-minute intervals. The data collected shall be reported quarterly to the Interagency Committee. This requirement is met by the existing USGS gaging station no. 15261000 at the mouth of Cooper Creek, which records temperatures at 15-minute increments year around. Cooper Lake Release to Cooper Creek: January – 10 cfs February – 10 cfs March – 10 cfs April – 10 cfs May – 10 cfs June – 20 cfs July – 25 cfs August – 20 cfs September – 20 cfs October – 15 cfs November– 10 cfs December – 10 cfs Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-3 Supporting Design Report – FINAL 14 June 2012 2.2 ASSUMPTIONS Assumptions include: Maximum Depth of Ice Cover – 4 feet Pre-Diversion Cooper Lake Inflow, 95% Exceedence Flow – 6.5 cfs Pre-Diversion Cooper Lake Inflow, 5% Exceedence Flow – 235 cfs Dam Facilities Inaccessible due to Snow – November 1 to April 30 Flow release from Cooper Lake to Cooper Creek may be required in addition to the 150 cfs requirement at the mouth of Cooper Creek for the Flushing Flow criteria. Flushing Flow is not a defined value and will be set by the Interagency Committee; therefore, it may be possible for some water to be diverted from Stetson Creek to Cooper Lake while the remainder of Stetson Creek flow is provided for flushing. Gate, valve and other water release settings need not be adjusted from November through April. Lake will be lowered to EL 1,160 during construction. Per the Settlement Agreement, the MIF will be determined annually by the Interagency Committee. Based on the estimated total flow at the diversion site, approximately 0.2 cfs on average is available to be released over an average year. Therefore, for use in this Design Basis Report, the MIF in Stetson Creek will be constant throughout the year and will be the maximum amount remaining (i.e., 0.2 cfs) after the required 18,285 ac-ft to Cooper Lake through the Diversion Pipeline in an average year. When necessary, Cooper Lake will be drawn down to provide the required flow release to Cooper Creek. 2.3 GOVERNING CODES AND STANDARDS The following codes, standards, and specifications are generally included as part of the design criteria. The applicable version of each document was the latest edition in force at the time the project design was started, August 2011, unless noted otherwise. All structures and systems will be designed, purchased, and installed in accordance with the requirements specified herein, including all references. References to specific codes and standards will be included in the applicable technical specifications of the contract documents. The civil, hydraulic and structural design, engineering, materials, equipment, and construction will conform to the specified codes and standards of the following organizations: AASHTO American Association of State Highway and Transportation Officials ACI American Concrete Institute AISC American Institute of Steel Construction ASCE American Society of Civil Engineers ASTM ASTM International Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-4 Supporting Design Report – FINAL 14 June 2012 AWWA American Water Works Association NWS National Weather Service USACOE U.S. Army Corps of Engineers USBR U.S. Department of the Interior, Bureau of Reclamation The mechanical and electrical design, engineering, materials, equipment, and construction will conform to the specified codes and standards of the following organizations: ANSI American National Standards Institute AISC American Institute of Steel Construction ASME American Society of Mechanical Engineers ASTM ASTM International AWS American Welding Society AWWA American Water Works Association CMAA Crane Manufacturer’s Association of America ICC International Code Council IEEE Institute of Electrical and Electronics Engineers NACE NACE International NEC National Electrical Code, 2008 NEMA National Electrical Manufacturers Association NESC National Electrical Safety Code NETA National Electric Testing Association NFPA National Fire Protection Association SSPC The Society for Protective Coatings UL Underwriters Laboratory The documents listed in the following subsections form a part of this report by reference thereto. 2.3.1 Civil and Structural Engineering 1. AASHTO (2007). “LRFD Bridge Design Specifications”, revisions by California Department of Transportation (Caltrans). 2. ACI (2011a). “Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (ACI 318R-11)”, Reported by ACI Committee 318. 3. ACI (2005b). “Guide to Shotcrete (ACI 506R-05)”, Reported by ACI Committee 506. 4. ACI (2003). “Manual of Concrete Practice”, Parts 1, 2, 3, 4, 5 and 6.” 5. ACI (2006). “Code Requirements for Environmental Engineering Concrete Structures and Commentary”, Reported by ACI Committee 350. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-5 Supporting Design Report – FINAL 14 June 2012 6. AISC (2007). “Steel Construction Manual” – Load and Resistance Factor Design/Allowable Stress Design”, Thirteenth Edition. 7. AISI (American Iron and Steel Institute) (Revised Ed., 1989). “Welded Steel Pipe”, Steel Plate Engineering Data-Volume 3. 8. ASCE (2005). “ASCE 7-05: Minimum Design Loads for Buildings and Other Structures.” 9. AWWA (2004). “Steel Pipe – A Guide for Design and Installation, Manual of Water Supply practices M11”, Fourth Edition. 10. Brater, Ernest F. et. al., (1996). “Handbook of Hydraulics,” Seventh Edition. 11. CSI (Computers and Structures, Inc.) (2009). SAP 2000 finite element Software. 12. FERC (Office of Hydropower Licensing) (2003). “Engineering Guidelines for the Evaluation of Hydropower Projects”, November 5. 13. Fortney, J.W. and Tiry, Robert F. (1972). “Flow-Induced Transverse Vibrations of Trashrack Bars”, ASCE Civil Engineering, May. 14. Gulliver, J. S., Lindblom, K. C. and Rindels, A. J., (1986). “Designing Intakes to Avoid Free-Surface Vortices”, Water Power and Dam Construction, September. 15. ICC (2006), International Building Code (IBC), 2006. 16. USACOE (1959). “Manual: Hydraulic Design Criteria, Volumes 1 and 2”. 17. USACOE (1980). EM 110-2-1602, “Hydraulic Design of Reservoir Outlet Works”, October 15. 18. USACOE (1995). ER 1110-2-1806, “Earthquake Design and Evaluation of Civil Works Project”, July 31. 19. USACOE (1989b). EM 1110-2-2502, “Retaining and Flood Walls”, September 29. 20. USACOE (1992). EM 1110-2-1603, “Hydraulic Design of Spillways”, August 31. 21. USACOE (1994). EM 1110-2-2105, “Design of Hydraulic Steel Structures”, May 31. 22. USACOE (2003a). EM 1110-2-2400, “Structural Design and Evaluation of Outlet Works”, June 2. 23. USACOE (2001). EM 1110-2-1612, “Engineering and Design: Ice Engineering”, October 30. 24. USBR (1976). “Design of Gravity Dams”. 25. USBR (1978). “Hydraulic Design of Stilling Basins and Energy Dissipators, Engineering Monograph No. 25”, January. 26. USBR (1981). “Concrete Manual”. 27. USBR (1987a). “Design of Small Dams,” Third Edition, a Water Resources Publication. 28. Zipparro, V.J. and Hasen, H. (1993). “Davis’ Handbook of Applied Hydraulics, Fourth Edition”. 29. Zowski, Thaddeus, (1960). “Trashracks and Raking Equipment; Part One – Trashracks”, Water Power, September. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-6 Supporting Design Report – FINAL 14 June 2012 2.3.2 Geotechnical Engineering 1. ASCE (2001). “Design and Construction of Frost Protected Foundations” (ASCE 32-01). 2. ICC (2006), International Building Code (IBC), 2006. 3. PTI (Post Tensioning Institute) (2004). “Recommendations for Prestressed Rock and Soil Anchors” (PTI DC35.1-04). 4. USACOE (1980). EM 1110-1-2907, “Rock Reinforcement”, February 15. 5. USACOE (1994). EM 1110-1-2908, “Rock Foundations”, November 30. 6. USACOE (1995). EM 1110-2-1614, “Design of Coastal Revetments, Seawalls and Bulkheads”, June 30. 7. USBR (1987). “Design of Small Dams”, Third Edition. 2.3.3 Mechanical Engineering 1. ASME (2001). “Boiler and Pressure Vessel Code, Section VIII”, July 1 with addenda. 2.3.4 Electrical Engineering 1. National Electrical Code – 2008 (NEC). 2.4 GENERAL STRUCTURAL CRITERIA 2.4.1 Material Properties Material properties have been determined during field investigations and laboratory testing. The following identifies the material properties used during the design of the Project facilities: 1. Water: - Unit weight 62.4 pounds per cubic foot (pcf) - Quality (Aqueduct or reservoir water for concrete production) 2. Structural Concrete: - Unit weight 150 pcf - Unconfined compressive strength f'c = 4,000 psi - Coefficient of thermal expansion 0.0000055/degrees F 3. Reinforcing Steel ASTM A615, Grade 60 4. Rock: - Unit weight 170 pcf - Deformation modulus 4.1x106 psi - Friction coefficient at concrete rock interface 0.48 - Cohesion at concrete rock interface 390 psi Stetson Creek Diversion and Cooper Lake Dam Facilities Page 2-7 Supporting Design Report – FINAL 14 June 2012 2.4.2 Structural Loads Different loads will actually or potentially act on the structures. The primary loads considered for the design are as follows: 1. Dead Loads: The dead load of the structure is the weight of concrete and steel. For final reinforced concrete design, the unit weight of concrete shall be assumed to be 150 pcf. Structural steel shall be designed based on a unit weight of 490 pcf. 2. Live Loads: Design live loads shall be as follows: - Working floors and grated areas 100 psf 3. Hydrostatic Loads: A triangular distribution of static water pressure shall be assumed acting normal against the faces of the structures exposed to water, varying from zero at the water surface. The dynamic pressure of water flowing toward structures shall be in accordance with AASHTO. 4. Uplift Loads: Uplift pressure on the base of structures exposed to the creek or reservoir shall be considered equal to the reservoir head at the base, unless otherwise determined by hydraulic modeling. 5. Earthquake Loads: Earthquake loads shall be applied in accordance with the IBC. 6. Ice Loads: Ice loads due to weight on structures shall be applied in accordance with ASCE 32-01 and ASCE 7-10. Ice loads on dams due to freezing reservoir water shall be applied in accordance with USACOE EM 1110-2-1612, and shall be based upon NOAA climate records. 7. Wind Loads: Wind loads shall be applied in accordance with the IBC. 8. Earth and Rock Loads: See relevant sections of this report. 9. Pipe Thrusts: Pipe thrusts due to unbalanced internal water pressure will exert unbalanced forces on the piping. Pipe thrusts will be a function of the maximum design pressure for which the pipe is designed. Thrust blocks and mass concrete shall be designed to resist excessive pipe thrusts and transfer the loads to the foundation. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-1 Supporting Design Report – FINAL 14 June 2012 3.0 FEATURE-SPECIFIC DESIGN CRITERIA Feature-specific design criteria and assumptions are summarized by design feature in the below subsections. 3.1 COOPER LAKE DAM ACCESS ROAD 3.1.1 Feature Description Road access to the site is via an existing gated 4.5-mile, single lane gravel road from the Sterling Highway near Cooper Landing to the Cooper Lake Dam. Access to the site may also be possible by way of Snug Harbor Road. In the summer it may be possible to launch small barges or boats at a primitive boat launch located at the termination of this road. Ice roads between the boat launch and the site may be feasible during winter months to accommodate larger equipment and supply deliveries. 3.1.2 Design Criteria and Assumptions 3.1.2.1 Chugach Responsibilities Chugach to maintain the Cooper Lake Dam access road for periodic, four-wheel drive, light-vehicle access to the site. 3.1.2.2 Contractor Responsibilities Contractor will be required to make improvements to the existing Cooper Lake Dam access road he deems necessary to bring his equipment and materials into the site, including improvement of wet areas, sharp curves, narrow areas, etc. that may limit delivery of equipment and materials to the site without improvement. At the end of construction the contractor will be required to leave the existing Cooper Lake Dam access road in as-good or better condition than he found it at the beginning of construction. The contractor may mobilize equipment and supplies to staging areas near Cooper Lake Dam by barge. This approach would likely require constructing temporary in-water improvements such as a boat launch at the end of Snug Harbor Road and near Cooper Lake Dam. Required maintenance and upkeep to Snug Harbor Road and spur roads due to construction traffic will be the responsibility of the contractor. At the end of the project the contractor will remove any temporary in water improvements and restore Cooper Lake Dam access road, Snug Harbor Road and spur roads to pre-existing conditions. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-2 Supporting Design Report – FINAL 14 June 2012 3.2 DIVERSION DAM AND DIVERSION INTAKE STRUCTURE 3.2.1 Feature Description The Diversion Dam Site is about 1.2 miles upstream of the confluence of Cooper Creek and Stetson Creek, at EL 1,424. For comparison, the historical USGS Gage 15260500 was about 0.3 miles upstream of the confluence. There is a natural falls about 60-feet high below the Diversion Dam Site. The Diversion Dam structure will consist of a dam/weir structure across the channel to create a diversion pool and side channel Diversion Intake Structure feeding the Diversion Pipeline. The crest of the Diversion Dam is sized based on sufficient submergence over the Diversion Intake of approximately 5 feet inclusive of losses through over the intake weir and trashrack, to pass 110 cfs to the Diversion Pipeline without significant air entrainment. Because the Pipeline is designed to pass a range of flows it can accommodate air entrainment without loss of capacity. To minimize excavation for the Diversion Dam, and given that the bed of the creek at this location is hard rock, the invert of the intake was set just below the creek bed at EL 1,421.5 to provide sufficient cover for the pipe. With a 36-inch diameter pipe inlet, the minimum required pool elevation is 1,430. The intake structure side channel spillway crest was set at EL 1,428.0 to provide the full 110 cfs without overflow downstream. The dam will be formed by a vertical concrete wall keyed and anchored to sound rock extending across the channel at the diversion location. The width of the dam open to flow, the Diversion Spillway, is 17.5 feet. The spillway is sized to pass the 100-year flood, about 810 cfs. This corresponds to about 6.0 feet of head over the spillway crest, setting the sidewall height at about EL 1,436.0. The intake structure side channel spillway will extend 17 feet upstream and be protected by a trashrack over the spillway crest and a grating over the open top of the structure. The top of sidewalls of the intake channel will extend to the top of the dam sidewalls, EL 1,436, or higher as required to retain the hillside. The invert of the intake channel will match the Diversion Intake Structure invert, EL 1,121.5. The trashrack will extend to the elevation of the crest of the main spillway. During the winter months ice will form on the surface of the pond created by the Diversion Dam. Depending on the length of time temperatures are below freezing and the flow rate in the creek, there may be a significant buildup of ice on the trashrack and within the inlet. Because of this, a hanging concrete wall will be constructed to preclude the entry of ice and insulated to inhibit the formation of ice inside of the intake structure. Polyethylene trashracks will be used to minimize ice accumulation. Because the flow is fairly low in the winter some buildup of ice will not affect the capacity of the inlet. However, it is possible that the trashrack could ice over completely and may shut off all the flow to the Diversion Pipeline. Since there is no access to the site in the winter, the trashrack is specified to withstand complete closure. A 36-inch square sluice will be installed adjacent to the Diversion Intake to allow periodic flushing of sediment and debris that may accumulate in front of the Intake structure. The invert Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-3 Supporting Design Report – FINAL 14 June 2012 of this opening is set at EL 1,421.5. The sluice will also provide a means of passing the MIF by opening the gate a small amount. 3.2.2 Design Information 3.2.2.1 Hydrology The hydrology of Cooper and Stetson creeks was assessed in the August 2004 Potential Cooper Creek Protection, Mitigation and Enhancement Measures (PME) Report developed by MWH for Chugach. As stated in the PME Report, USGS Gage 15260500 was located on Stetson Creek close to its confluence with Cooper Creek. The site selected for the Diversion Dam is a significant distance upstream of the historical gage and, therefore, required adjusting the hydrology at the Diversion Dam site based on the reduced drainage area. The drainage area for the Diversion Dam site is about 7.7 square miles, compared to the entire drainage area at the USGS gage of 8.6 square miles. Thus, the flow at the USGS gage was reduced by about 10% to make it applicable to the Diversion Dam. Therefore, the Stetson Creek MIF could be met by flow not captured by the Diversion Dam or “from the total amount of water available for release to Cooper Creek” as indicated in the Settlement Agreement (i.e., from the 10,256 ac-ft volume). Stetson Creek flow data measured at the USGS gage and estimated at the Diversion Dam site are presented in Table 3-1. Table 3-1 Estimated, Average Monthly Stetson Creek Flow at USGS Gage 15260500 and Diversion Dam Site Month Average Flow at USGS Gage 15260500 (cfs) Estimated Average Flow at Diversion Dam (cfs) January 10.4 9.3 February 8.5 7.6 March 5.9 5.3 April 8.9 7.9 May 39.4 35.3 June 83.3 74.6 July 55.4 49.6 August 32.2 28.9 September 30.5 27.3 October 32.2 28.8 November 21.8 19.6 December 13.5 12.1 Key: cfs – cubic feet per second USGS – U.S. Geological Survey Table 3-1 was developed based on the hydrologic analysis of Cooper and Stetson Creeks in the PME Report. The percentage of flow at the mouth of Cooper Creek estimated to come from Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-4 Supporting Design Report – FINAL 14 June 2012 Stetson Creek, developed in the PME Report, was applied to an extended period of record for flows at the mouth of Cooper Creek. The period of record was extended from that in the PME Report to include data from 1998 through 2008. Average Stetson Creek flows listed in Table 3-1 result from applying the estimated percentage in the PME report to the average monthly flows for the extended period of record. For the purposes of this report the flows in Table 3-1 were reduced 10% to obtain flows at the Diversion Dam. Thus, the design flow of 110 cfs for the Diversion Pipeline corresponds to about a 1.5% exceedence flow in Stetson Creek at the Diversion Dam (about 120 cfs at USGS Gage 15260500), as presented in Graph 3-1. Graph 3-1 Estimated, Post-Cooper Lake Dam, Stetson Creek Flow Exceedence Curve at USGS Gage 15260500 3.2.2.2 Hydraulics 3.2.2.2.1 Annual Diversion The Settlement Agreement states 18,285 ac-ft must be diverted from Stetson Creek to Cooper Lake annually. Of that volume, 10,256 ac-ft is to be released from Cooper Lake to Cooper Creek leaving a net volume of 8,029 ac-ft to be used for power production through the project power plant. The Settlement Agreement also states that on an annual basis some MIF may be directed to be maintained in Stetson Creek “(if any) from the total amount of water available for release to Cooper Creek” (i.e, the MIF is taken from the 10,256 ac-ft volume and does not affect the net Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-5 Supporting Design Report – FINAL 14 June 2012 volume remaining for power production). No specific MIF quantity is stated, indicating that only that the Interagency Committee will provide direction annually for MIF below the Diversion Dam, “if any”. As shown in Table 3-2, only about 0.2 cfs (average flow) can be maintained in Stetson Creek as MIF, if 18,285 ac-ft is diverted, without taking additional MIF from the Cooper Creek release volume (i.e., 10,256 ac-ft). Table 3-2 Average Monthly Diversion Flows Month Flow at Diversion Dam, Average (cfs) *Stetson Creek MIF (cfs) Diversion Flow (cfs) Diverted Volume (ac-ft) January 9.3 0.2 9.1 550 February 7.6 0.2 7.4 410 March 5.3 0.2 5.1 310 April 7.9 0.2 7.7 450 May 35.3 0.2 35.1 2,150 June 74.6 0.2 74.4 4,420 July 49.6 0.2 49.4 3,030 August 28.9 0.2 28.7 1,760 September 27.3 0.2 27.1 1,610 October 28.8 0.2 28.6 1,750 November 19.6 0.2 19.4 1,150 December 12.1 0.2 11.9 730 Total - --18,320 * Indicates the average MIF without reducing the volume released from Cooper Lake to Cooper Creek. Releasing this flow continually is not practical or suggested. Two points should be made relative to Table 3-2. First, the flows in the table are average monthly flows recorded over a period of 65 months. Based on the average daily record for the period it is estimated that there were a total of 22 days (about 4 days per year) that exceeded the proposed maximum diversion of 110 cfs for a total “lost” volume past the Diversion Dam of 860 ac-ft or about 170 ac-ft per year. (It should be noted that about 25% of that 5+ year volume occurred during one day.) That would leave about 7,860 ac-ft available for power production annually. If 70 cfs were the maximum diverted through the Diversion Pipeline then about 4,800 ac-ft would be “lost” to generation or about 960 ac-ft per year, leaving about 7,070 ac-ft annually for power production. The second point is that it is assumed that about 11% more flow than flows into the Diversion Dam site, as indicated in Table 3-2, is added by accretion below the Diversion Dam or nearly 3 cfs on average at the mouth of Stetson Creek, providing measurable MIF below the point of diversion. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-6 Supporting Design Report – FINAL 14 June 2012 3.2.2.2.2 Diversion Intake Structure Design Design of the intake structure at the Diversion Dam is based on inlet control. Sufficient head over the crown of the pipe at the inlet is required to pass the desired flow and minimize air entrainment. Air entrainment and vortexing are not a concern with selected arrangement as they do not affect the discharge capacity significantly and there is an air inlet/outlet pipe provided on the pipe a short distance downstream of the Diversion Dam. During low flows in Stetson Creek the pipe will be flowing only part flow and the inflow will cascade over the diversion weir entraining large amounts of air. A horizontal baffle is provided to extend the flow path length and allow most of this entrained air to leave the flow before it enters the pipe. Any residual air will be handled by vents along the pipeline downstream. Calculations supporting the hydraulic design of the diversion intake structure are presented in Appendix B. 3.2.2.3 Geotechnical Design 3.2.2.3.1 Geotechnical Design Criteria The diversion dam site is located in a narrow valley having steep side slopes. The slopes at the upper elevations are mantled by overburden soils primarily consisting of glacial outwash materials. The underlying rock is comprised of fresh to slightly weathered, moderately hard slate. However, in some locations the fresh rock is obscured by rock disturbed as a result of stress-relief or structurally controlled displacements. This is most notable in the steeper portions of the abutments. Slightly weathered rock is present in the valley floor. Required excavation depths are anticipated to be range from 2 feet at the base of the diversion dam to upwards of 13 feet near the higher elevations of the left abutment. Excavations on the order of about 5 feet are anticipated to reach suitable rock near the upper portions of the right abutment. In general, the diversion dam foundation has been designed and prepared in accordance with the recommendations of the United States Bureau of Reclamation (USBR) guidelines as presented in The Design of Small Dams, 3rd Edition (1987). Bearing capacity and foundation deformation characteristics of the diversion dam can be determined based on the geotechnical parameters presented in Table 3-3. The supporting bearing capacity equations are presented in Appendix B. Table 3-3 Diversion Dam Foundation Design Parameters Diversion Foundation Parameters for Slate Design Value Bearing Capacity1 (psf) 12,000 psf Coefficient of Friction (Rock-Concrete Interface) 0.48 Seismic Site Class B 0.2 Second Seismic Coefficient (Ss) 2 1.773 g 1.0 Second Seismic Coefficient (S1)2 0.657 g Notes: 1. Bearing Capacity estimated based on feasibility layout. Modifications to the feasibility may affect (increase or decrease) the allowable bearing capacity. 2. Ss and S1 are based on values for a Site Class B. These values were adjusted during design based on site class in accordance with the IBC (2006). Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-7 Supporting Design Report – FINAL 14 June 2012 Preparing the abutments of the diversion dam will require constructing permanent slopes in rock and potentially small amounts of overlying soil. Slope stability of rock in the abutments and adjacent areas can be evaluated using the soil and rock parameters presented in Tables 3-4 and 3- 5, respectively. Permanent abutment slope stability and required stabilization measures have been evaluated and designed through kinematic and limit equilibrium analyses using the Rocscience™ software Dips™, Rocplane™, and Swedge™. These analyses were based on statistically significant data sets from 367 observed discontinuities at the project site. The abutment slope stability calculations indicate acceptable factors of safety with the use of appropriate slope support and drainage as indicated on the project drawings and in the specifications. The abutment slope stability calculations are presented in Appendix B of this report. Table 3-4 Soil Properties and Strength Design Parameters Soil Type Moisture Content (%) Dry Unit Weight (pcf) Internal Friction Angle (degrees) Cohesion (psf) Maximum Permanent Slope Structural Fill (Fine Grained) 20 98 30 0 2.5H:1V Structural Fill (Course Grained) 10 115 38 0 2H:1V Undisturbed Native Silt 30 92 33 0 2.5H:1V Undisturbed Glacial Outwash 8 115 36 0 2H:1V Undisturbed Glacial Till 9 120 39 0 2H:1V Angular Rock Fill 6 120 42 0 1.5H:1V Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-8 Supporting Design Report – FINAL 14 June 2012 Table 3-5 Rock Strength Design Parameters Parameter Parameter Value Intact Rock Unconfined Compressive Strength 8384 psi Young’s Modulus 12,269,000 psi Slate Joint Strength Base Friction Angle 28 degrees Roughness Factor 5 degrees Cohesion 385 psi Mohr-Coulomb Fit Rock Mass Internal Friction 28 degrees Rock Mass Cohesion 390 psi Rock Mass Parameters Tensile Strength 36 psi UCS 600 psi Global Strength 1290 psi Deformation Modulus 4,065,650 psi 3.2.2.3.2 Geotechnical Site Investigations Geotechnical site investigations for the diversion dam, pipeline, and outlet works are fully documented in the Report of Geotechnical Engineering Services (MWH, March 2011). The aforementioned separate report includes all boring logs, geology reports and laboratory test reports for the Project. 3.2.2.3.3 Site Suitability and Reservoir Rim Stability Assessment The site of the Stetson Creek Dam and Reservoir was selected as the most suitable of four potential locations that were identified and evaluated during preliminary design stages. The dam location was selected as the most favorable based on geologic site conditions of the dam and the corresponding diversion pipeline, hydraulic requirements, stream flow targets, frequency of avalanche occurrence, and site access. Assessments of the site were based on data obtained through review of previous geologic and geotechnical assessments of the site and region, interpretation of aerial photographs, geological site reconnaissance, avalanche risk assessment, geotechnical rock core borings, seismic refraction surveys, in-situ water pressure testing, and laboratory testing. These data were used as the basis of our design and assessment of the suitability of the dam site and reservoir. The selected dam site is located at a narrow portion of the Stetson Creek canyon. Slate bedrock can be observed within the base of the stream and in the lower portions of both the left and right abutments. Based on rock core borings and seismic refraction surveys conducted on both abutments, the bedrock on the upper abutments is overlain by a relatively thin layer of displaced rock. A thin layer of displaced rock overlying intact bedrock is common throughout the region in occurrences of slate and can be observed in numerous locations along Stetson Creek and the Cooper Lake Dam access road. Site investigations indicate that the under laying rock is fresh to slightly weathered and moderately hard based on USBR classifications (generally fresh and Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-9 Supporting Design Report – FINAL 14 June 2012 strong based on ISRM classifications). Water pressure testing of the rock formation or the dam abutments yielded lugeon values of less than one, suggesting that the formation is relatively tight at these locations. Observation of rock structure suggests that two primary discontinuity (bedding and joint) sets are present, which dip at approximately 85 degrees to the east-northeast and 53 degrees to the southeast. Based on site observations, available data, and the results of our analyses, the proposed site is suitable for the support of the Stetson Creek Dam when founded on intact bedrock and constructed in accordance with the project drawings and specifications. The reservoir that will be impounded by the Stetson Creek Dam will be very small, having a volume of approximately 0.2 acre-ft. It will be on the order of 100 feet long and will be 9.5 feet deep at the base of the dam under normal operating conditions. The reservoir rim will be comprised of slopes that extend hundreds of feet in elevation above the reservoir surface. The reservoir area has been evaluated by reviewing topography, aerial photographs, and conducting a geologic reconnaissance. No topographical features, geologic hazards, or other observation have been identified within the reservoir area that would result in instability of the reservoir. 3.2.2.4 Stability Design The structural stability assessment of the Diversion Dam included static and seismic conditions. For seismic conditions, the Diversion Dam has been pseudo-statically analyzed as a “low” hazard potential dam in accordance with the stability requirements specified in Chapter 3 of the FERC, “Engineering Guidelines for the Evaluation of Hydropower Projects.” Loads applied included hydrostatic forces resulting from normal and flood levels, uplift, ice loading, and earthquake, including Westergaard hydrostatic forces. Load combinations were based on FERC requirements which consist of: Case I - Normal Operating Condition; Case II – Flood Discharge Loading; Case IIA – Ice Loading; Case III – Case I + Earthquake. Additional load combinations that shall be analyzed are Post-Earthquake, Construction, and Construction with Earthquake. Dam shall be designed to meet minimum stability and stress criteria listed below, as specified in USACE EM 1110-2-2200: Load Condition Resultant Location at Base Foundation Bearing Pressure Concrete Compressive Stress Usual Middle 1/3 <= allowable 0.3 fc’ Unusual Middle 1/2 <= allowable 0.5 fc’ Extreme Within base <= 1.33 x allowable 0.9 fc’ Sliding stability of dam met the minimum FERC requirements as listed below (with cohesion assumed): Load Condition Factor of Safety Usual 2.0 Unusual 1.25 Post-Earthquake Greater than 1.0 Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-10 Supporting Design Report – FINAL 14 June 2012 3.2.2.4.1 Stability Calculations The stability of the diversion dam was analyzed for eccentric loading, sliding, bearing pressure, and flotation. These evaluations were considered for following load cases: Normal – Operating conditions (reservoir pool at El. 1430 ft); Normal – Winter conditions (reservoir pool El. 1430 ft. and ice loads); Unusual – Flooding (reservoir pool El. 1436.5); Extreme – Maximum design earthquake (reservoir pool El. 1430 ft, seismic forces) Unusual –Post-earthquake conditions (reservoir El. 1430 ft, residual sliding resistance forces); Unusual – Construction (no reservoir pool, dam fully constructed) Extreme – Construction Earthquake (no reservoir pool, seismic loads) For each of the load cases listed above, sliding conditions were considered along the rock- concrete interface of the dam, as well as along a hypothetical through-going joint parallel to the base of the dam in order to identify and evaluate the most critical site conditions. The analyses conducted resulted in acceptable factors of safety for each of the stability modes and load cases considered. Calculation details are presented in Appendix B. 3.2.2.4.2 Seismic Load Determination The spectral response acceleration and corresponding seismic loads for the site were determined in accordance with the 2009 International Building Code using the USGS Seismic Hazard Curves and Uniform Hazard Response Spectra application version 5.0.9a. 3.2.2.5 Structural Design The structural design of the Diversion Dam and Diversion Intake Structure shall be in accordance with the codes, standards and applicable loadings indicated under Section 2 and the geotechnical design criteria and structural load cases indicated above. 3.2.2.6 Flow Control and Monitoring The Diversion Intake sluice gate will be manually operated. The intake to the Diversion Pipeline will remain open position except when the Pipeline is taken out of service for maintenance or repair. For this case a slide gate is placed in front of the pipe opening. The dam sluice gate will remain in the closed position except to provide the required MIF, if any, as determined in consultation with the Interagency Committee or for maintenance/sluicing. The flow in the Diversion Pipeline will be monitored as indicated under Section 3.6. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-11 Supporting Design Report – FINAL 14 June 2012 3.2.3 Access Access to the Diversion Dam will be provided via the current access road and the Diversion Pipeline bench. The current dam access road runs from the Sterling Highway to Cooper Lake Dam. This road will be upgraded as required by the contractor to complete the work as part of the overall construction effort as discussed elsewhere. It is about 1.8 miles from the Cooper Lake Dam to the Diversion Dam site along the Diversion Pipeline. The associated soil cut and fill slopes of the diversion access road will be hydroseeded at the completion of construction; however, it is expected that nominal maintenance will be performed on the road to maintain year-round vehicle/equipment access to the Diversion Dam. Helicopter, four-wheel drive vehicle, ATV and foot access are anticipated to be the primary operating access methods. The Diversion Dam will likely be completely inaccessible from about November through April due to snow. 3.2.4 Construction In general, construction sequencing will require substantial completion of the construction of the diversion access road before construction can begin on the Diversion Dam. There is some flexibility in the construction sequencing for the pipeline in relation to the Diversion Dam depending on the methodology used by the construction contractor. Cofferdamming will be required to isolate work areas for construction in the dry. The Project specifications require that the contractor develop and submit plans for dewatering the work areas. It is anticipated that the contractor will either (1) construct staged cofferdams at the Diversion Dam site and construct the structure in halves or (2) construct a temporary diversion dam upstream of the Diversion Dam site and pipe the flow around the construction area. Delivery and placement methods for concrete are likely to be by truck and concrete pump. The selected contractor will either utilize established concrete batch plants in the project vicinity for production and delivery of concrete, mobilize a small batch plant for on-site production near the Cooper Lake Dam, or site mix concrete in trucks from dry, pre-mixed, concrete, one cubic yard supersacks. Helicoptering of batched concrete from near the Sterling Highway, or other location in the vicinity of the Project, to the Diversion Dam may also be a viable concrete delivery method. 3.2.5 Maintenance Maintenance activities at the Diversion Dam are expected to be seasonal. As snow usually covers the area from November through April, it is expected that the Diversion Dam must operate without maintenance during this period. When the area thaws in May, Chugach staff can access the Diversion Dam via the pipeline right-of-way or by helicopter or foot to reset the gate (if necessary), sluice the reservoir, clean the trashrack, remove any debris on or near the facility, and repair any damage that may have occurred over the winter. As discussed above, the sluice gate and Diversion Intake slide gate will be able to be operated manually. Hand rakes to clean the trashracks, chainsaws, shovels, and other tools to remove debris, and any tools necessary for repairs will have to be brought in with Chugach staff. The Diversion Dam should be inspected for damage and to clean the trashrack periodically from May through October. Particular attention may be required in the fall during the leafy season to clean the trashracks. Hatches are Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-12 Supporting Design Report – FINAL 14 June 2012 provided through the intake deck to accommodate manual raking. Additional visits by Chugach staff may be required to adjust the Diversion Intake gate based on flow requirements. Before winter begins, Chugach staff will perform a final inspection of the Diversion Dam, removing debris, cleaning the trashrack, making final repairs, and setting the Diversion Intake gate to its winter setting. 3.3 DIVERSION PIPELINE AND CONSTRUCTION ACCESS 3.3.1 Feature Description The diversion pipeline will be placed either within, or on top of, an associated construction assess road bench as discussed below. For the majority of the alignment, the pipeline will be buried with a minimum cover thickness of 3 feet. Where the pipeline is constructed in the Stetson creek gorge, conditions may be such that the pipeline will be placed on top of the pipeline bench to reduce rock trenching. A diversion access road will be constructed along the pipeline alignment to provide access to the Diversion Dam, the pipeline itself, and the diversion outfall. The access road will initially be sized at 15 feet (30% design) and adjusted as needed during the final design process to optimize earthwork volumes, constructability and long-term Chugach access needs. 3.3.2 Design Information 3.3.2.1 Pipeline Routing The alignment was determined by optimizing grading, minimizing constructability issues from topographic features, minimizing geologic hazards and avoiding impacts to wetlands. 3.3.2.2 Pipeline Materials The design includes an HDPE pipeline with an inside diameter of approximately 36 inches (nominal 42-inch HDPE) with a standard dimension ratio of 21 and a strength rating for an internal pressure of 100 psi. The standard dimension ratio 21 pipe has been selected to accommodate trench fill and traffic live load (external pressure). The pipeline slope and hydraulic grade line have been designed to operate as generally a partially full pipe from the diversion intake structure to Cooper Lake. The pipe runs full through the instrumentation vault at pipeline station 95+50 +/- with an internal pressure of less than 10 psi, which is also the case from about stations 103+00 to 111+00. 3.3.2.3 Pipeline Hydraulics As the flow in the pipeline is controlled from the upstream end (See Section 3.2.2.5) the flow in the pipe will be open channel with large segments flowing full under design flow conditions. Standpipes will be provided along the pipeline at breaks in grade to allow air to freely enter/or exit the pipeline. Calculations supporting the hydraulic design of the diversion pipeline are presented in Appendix B. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-13 Supporting Design Report – FINAL 14 June 2012 3.3.2.4 Geotechnical Design The construction access road and pipeline will require cuts in slate and overburden soil. Rock cuts of up to approximately 40 feet high are anticipated along Stetson Creek between approximate diversion pipeline stations 0+00 and 12+50. In addition, significant soil cut slopes are anticipated throughout the remainder of the Stetson Creek reach of the diversion pipeline. Only minor amounts of fill will be required along the Stetson Creek reach of the pipeline and access road. Cut slopes along the Cooper Creek reach of the diversion dam are expected to be less than about 15 feet in height except in localized areas. In general, soil and rock fill generated from the Stetson Creek reach excavations to construct fills along the Cooper Creek reach to balance cut and fill volumes to the extent feasible. Rock slopes will be cut to slopes of 0.5 horizontal to 1 vertical (0.5H:1V) provided they are properly supported. Rock support were designed in accordance with accepted geotechnical practice. Rock anchors, where needed, have been designed as passive rock bolts that have been designed in general accordance with the Post-Tensioning Institute’s (PTI’s) recommendations for ground anchors (2004). Since rock strength can vary significantly with rock condition and rock mass structure. Rock mass strength is expected to vary with location, slope aspect, and rock conditions. Accordingly rock support type, spacing, and length should modified to meet field conditions, as needed. Calculations in support of rock slope design and slope reinforcement calculation are presented in Appendix B. Both glacial outwash and glacial till soils are expected to be present along the majority of the pipeline alignment; however areas of fine grained soil may be encountered along localized areas of the pipeline. Constructed slopes will be consistent with those presented in Table 3-4, unless alternate slopes are determined to be appropriate based on the engineer’s assessment of field conditions. The diversion pipeline and construction access road will be supported by a gabion retaining wall that extends from the diversion dam and intake structure to approximate road stationing 3+00. This wall has been designed in accordance with industry standards for gabion wall design. As precautionary measures, portions of the gabion wall will be armored with shotcrete and the wall will be doweled into the underlying rock foundation to resist erosional effects of Stetson Creek on the wall. Details of the gabion retaining wall design are presented in Appendix B. 3.3.2.5 Structural Design The structural design of the Diversion Pipeline and appurtenant structures shall be in accordance with the codes, standards and applicable loadings indicated under Section 2 and the geotechnical design criteria indicated above. 3.3.2.5.1 Rupture Calculations For the purposes of this section rupture calculation refer to pipe failure through buckling and compressive ring thrust (crushing). Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-14 Supporting Design Report – FINAL 14 June 2012 Buckling: Pipe buckling was checked for both standard trench installation and shallow cover installation given that 3 feet of pipe cover is effectively the division between the two cases. The standard trench installation case assumes that the pipe behaves as a membrane without a bending load developing at the pipe crown. At installation depths of less than one pipe diameter (shallow), the membrane action may not fully develop and live loads place a bending load on the pipe crown. For both analyses, live traffic loads were assumed as discussed in Section 4.3.1.2. The results of each analysis conducted indicate acceptable factors of safety for each of the cases considered. Calculation details are presented in Appendix B. Crushing: Crushing occurs when the compressive stress in the pipe wall from earth and live load pressure exceeds the compressive yield stress of the material. The live load used for crushing calculations is discussed in Section 4.3.1.2. The result of the analysis conducted indicates an acceptable factor of safety against crushing. Calculation details are presented in Appendix B. 3.3.2.5.2 Traffic Load Calculations The largest expected traffic load was used for rupture calculations. In this case, the largest traffic load was assumed to be a fully loaded articulated dump truck during construction. During operation, traffic loads can be expected to be from small trucks and maintenance equipment such as a backhoe or small dozer, all of which exert significantly less ground pressure than construction traffic. A fully loaded Volvo A40/A35 articulated dump truck operating directly above the pipeline was assumed for these calculations. 3.3.2.5.3 Thrust Calculations Heat fused HDPE pipe and fittings are a monolithic structure which does not require thrust blocks to restrain the longitudinal loads resulting from pipe pressurization (reference included in Appendix B). 3.3.3 Pipeline Bench / Pipeline Construction Access The width of the bench will be sufficient to provide access during construction activities and for maintenance use if maintained by Chugach. The bench will be constructed similar to an outsloped forest road. The bench surface will be canted to a drain to the downhill side, eliminating the need for ditch construction and relief culverts. Outsloping the pipeline bench allows the construction volume to be minimized as well as allowing for a reduction in runoff turbidity and erosion if properly constructed and maintained. Gravel surfacing will not be placed on the pipeline bench. Instead, the bench will be revegetated at the completion of construction. Gabion basket retaining walls are expected at select locations within the Stetson Creek gorge where side slopes are very steep (0.5H:1V) or where deep gullies must be crossed. It is anticipated that the Diversion Dam may be accessed along the route of the pipeline by a nominally maintained right of way without a bridge across the spillway. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-15 Supporting Design Report – FINAL 14 June 2012 At creek and gully crossings, culverts will be placed to convey flow beneath the pipeline. Culverts are sized to pass the 50-year 24-hour storm event. Culvert sizing calculations are presented in Appendix B. The alignment shown on the drawings intends to minimize construction within or adjacent to known wetland areas. 3.3.4 Construction The majority of the pipeline bench will be constructed as a cut-to-fill, with excavation material from the uphill side placed as fill on the downhill side. Where the bench is located within the Cooper Creek drainage, typical permanent cut and fill slopes in common material are expected to be 2V:1H. Where the bench is located within the Stetson Creek drainage, it will be constructed as a cut-to-fill only in locations where the existing side slopes are flatter than about 2H:1V. For much of the upper portions of the bench (above EL 1,350), the bench will be constructed as an excavation only, requiring removal of excavated material for use as fill in lower sections of the alignment. This pipeline cut above Stetson Creek will be difficult. Some to a considerable amount of blasted cut material can be expected to fall down the steep hillslope below the cut, some to the creek. The pipeline will be constructed as a trench and backfill operation after completion of the bench has been established. 3.3.5 Maintenance Maintenance of the pipeline is expected to be seasonal. As snow usually covers the area from November through April, it is expected that the Diversion Dam and the pipeline will operate without maintenance during this period. Low flow during the winter will decrease the water velocity in the pipeline and increase the possibility of ice formation in the pipeline. However, because the pipeline is buried and the composition of the pipeline is non-conductive HDPE, the water should remain above freezing in the pipeline. The rock slopes of the construction access road has been designed as a low volume, low risk road. Slope instability due to plane and wedge failure have will be mitigated with passive rock bolts. Toppling failures are expected to be relatively small due to the relatively low slope height and the anticipated small block size as a result of the closely spaced and persistent discontinuities. It is anticipated that some rock fall of relatively small blocks will occur, similar to rock fall observed in the existing Cooper Lake Dam Spillway. Accordingly occasional maintenance will be required to remove rock fall material. In the spring, maintenance personnel will conduct sufficient maintenance on the pipeline bench to prevent the establishment of deep rooted vegetation. It is expected that a two-man clearing crew with chainsaws will be sufficient for most maintenance. Clearing of drainage culverts, repair of small sloughing events, cleanup of minor rock falls, placement of additional fill in problem areas, and periodic reseeding along the pipeline can be expected on occasion. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-16 Supporting Design Report – FINAL 14 June 2012 3.4 DIVERSION OUTFALL 3.4.1 Feature Description The Diversion Pipeline connects directly to the outfall pipe which connects to a diffuser located on the bottom of Cooper Lake to minimize mixing of the colder water with the warmer upper lake water. 3.4.2 Design Information 3.4.2.1 Hydraulics and Siting The location of the Stetson Creek Diversion Outfall into Cooper Lake will be about 2,000 feet upstream of Cooper Lake Dam to minimize the effect of the colder, diverted water on the warmer, surface water releases from the dam. The steep slope of the lake bank (about 20%) is such that a hydraulic jump can be expected within the outlet pipe at flows smaller than the design flow, thus the outlet pipe will require air-venting capability to maintain the design discharge capacity and avoid discharge of air to the reservoir where it will disturb the thermocline. 3.4.2.2 Flow Diffusion The diffuser is designed to direct the diversion flow along the bottom of the lake. The objective is, to the extent possible, to not disturb the thermocline in the lake. The diffuser has four diffuser ports at the end of the pipe oriented to direct the flow perpendicular to the alignment of the outfall pipe angled 12.5 degrees above the lake bottom. 3.4.2.3 Geotechnical Design Physical structures associated with the diversion outfall will likely be founded on glacial outwash soils. Geotechnical design parameters have been determined based on anticipated structure layout, which are presented in Table 3-6. Table 3-6 Diversion Outfall Foundation Design Parameters Diversion Outfall Foundation Parameters for Glacial Outwash Design Value Strip/Spread Bearing Capacity1 (psf) 3,500 psf Slab on Grade Bearing Capacity 1,200 psf Coefficient of Friction (Soil-Concrete Interface) 0.44 Seismic Site Class C 0.2 Second Seismic Coefficient (Ss)2 1.779 g 1.0 Second Seismic Coefficient (S1)2 0.660 g Notes: 1. Bearing Capacity estimated based on feasibility layout. Modifications to the feasibility may affect (increase or decrease) the allowable bearing capacity. 2. Ss and S1 are based on values for a Site Class B. These values were adjusted during design based on site class in accordance with the IBC (2006). Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-17 Supporting Design Report – FINAL 14 June 2012 3.4.2.4 Structural Design The structural design of the Diversion Outfall has been conducted in accordance with the codes, standards and applicable loadings indicated under Section 2 and the geotechnical design criteria indicated above. Concrete collars shall be attached to all submerged pipe to act as ballast. Collars shall be sized as needed to resist upward buoyancy forces and any current conditions that may be present, but still allow a partially-filled pipe to be floated into position. The collar weight is based on a buoyancy allowance of 20 percent air in the pipe. Bottom footprint must be 25% larger than top to minimize overturning of collars. Calculations in support of the concrete collars are presented in Appendix B. 3.4.3 Construction The reservoir will be drawn down to between EL 1,160 and 1,165 prior to installing the pipeline and diffuser to minimize the depth of construction and to maximize the amount of trenching that can be performed in the dry. The lakeshore will be trenched, and the HDPE pipe will be fused and placed in the trench on the required bedding. The section along the lake bottom will be fitted with concrete weights and the diffuser ports capped. The pipe will then be floated into the reservoir on the required alignment and sunk by opening a valve in one of the diffuser port end caps. The pipe will settle to the bottom starting from the off-shore end. The on-shore end of the diffuser section will then be flanged to the end of the pipe. The pipe trench will then be backfilled. The Project specifications require the contractor to submit an installation plan for the Diversion Outfall Pipe. 3.4.4 Maintenance The diffuser should not require maintenance, although it should be inspected about every ten years. 3.5 SIPHON OUTLET WORKS 3.5.1 Feature Description The Siphon Option provides flow from Cooper Lake to Cooper Creek. The design flow for the siphon varies from 10 cfs up to 30 cfs. At the lower flow, the reservoir is assumed to be at the minimum historical reservoir level of EL 1,160.0 in April. At the higher flow the reservoir is at the historical minimum elevation of 1,170.0 in July, as shown in Graph 3-3. The design will not discharge 30 cfs at the lowest lake level. The inlet structure will be a precast concrete box containing a coarse HDPE trashrack and a check valve used for priming the pipeline. From the inlet structure, with a pipe invert at EL 1,151, a 30-inch diameter steel pipeline will slope downstream to a high point invert at EL 1,181 and trenched through the spillway at to a low point invert at EL 1179.0. The spillway cut will be approximately 30-foot deep through rock. This cut through the spillway will remain deep Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-18 Supporting Design Report – FINAL 14 June 2012 enough to avoid vapor lock of the siphon. The pipe will be surrounded with bedding material and the spillway cut will be backfilled with shotrock from the excavation. To prevent water from piping through the spillway along the siphon pipe, a concrete cutoff wall will be keyed into rock, reinforced and placed, encasing the pipe up to the original spillway elevation. The cutoff wall will be located near the axis of Cooper Lake Dam. The pipe will discharge to a gated outlet structure and rock lined stilling pool in Cooper Creek downstream of the spillway. To prime the siphon the sluice gate at the outlet structure is closed. The pipe will be filled via a 4-inch steel pipe tapped off of the Diversion Pipeline, and tapped to the siphon pipe near siphon pipeline STA 8+80. Because the fill line will be routed into the spillway on rocky slopes it will be encased in shotcrete. For freeze protection the fill pipe will be isolated with butterfly isolation valves at each end and a drain valve to prevent freezing while not in use. The isolation valves will be opened in the meter vault on the Diversion Pipeline STA 95+00± and in a manhole over the siphon pipe STA 8+80±. During filling, air will exit the pipeline during filling through a 3-inch vent line located near the high point of the siphon pipeline STA 6+00. The air vent will be routed to the fill line manhole and controlled by a valve in the fill manhole. When the siphon pipe is full water will exit from the air vent. At this time the air vent line and the fill line are closed and the fill line will be drained. The downstream sluice gate is opened to a pre-calculated opening to pass the required flow. 3.5.2 Design Information 3.5.2.1 Hydrology and Hydraulics The Settlement Agreement states that 10,256 ac-ft of water from Cooper Lake must be released into Cooper Creek every year to provide warmer water in the creek. The Settlement Agreement also states that 18,285 ac-ft of water should be diverted from Stetson Creek to Cooper Lake every year. This results in 8,029 additional acre-feet available for generation from Cooper Lake through the existing project powerhouse. The Settlement Agreement further states that if no direction regarding the release from Cooper Lake is received from the Interagency Committee, then target instantaneous flow releases and target monthly volumes will be set according to Table 3-7. When these flow releases are compared to the calculated diversions available from Stetson Creek, it is apparent additional drawdown of Cooper Lake will be required January through April. After April the lake will replace the volume deficit from the previous months and gain the additional 8,029 ac-ft of volume for generation. The water temperature data shown in the PME Report and as shown in Graph 3-2 indicates that the lake stratifies during the summer. However, the lake maintains a constant, warmer temperature above EL 1,150. It is for this reason that a single intake is designed with an invert of EL 1,154. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-19 Supporting Design Report – FINAL 14 June 2012 The lake level varies throughout the year. Historically, Cooper Lake fills in the summer and is drawn down in the winter. The changes in inflow and outflow at Cooper Lake, as shown in Graphs 3-3 and 3-4, will exacerbate the lake level drop and rise. Table 3-7 Targeted Cooper Lake Release Flow, Estimated Average Diversion Flows, and Estimated Cooper Lake Drawdown/Refill Month Diversion from Stetson Creek (cfs) Targeted Cooper Lake Release (cfs) Volume of Drawdown (-) or Refill (+) at Cooper Lake (ac-ft) January 9.1 10.0 -60 February 7.4 10.0 -140 March 5.1 10.0 -300 April 7.7 10.0 -140 May 35.1 10.0 1,540 June 74.4 20.0 3,240 July 49.4 25.0 1,500 August 28.7 20.0 530 September 27.1 20.0 420 October 28.6 15.0 840 November 19.4 10.0 560 December 11.9 10.0 120 Total - - 8,110 3.5.2.1.1 Routing The Siphon is routed through the spillway at a higher elevation than a gravity fed pipeline, minimizing the rock cut. The pipeline is sized based on the maximum instantaneous outflow of 30 cfs, prescribed in the Settlement Agreement. Our assumption is that only 10 cfs may be required to be released for lake levels down to EL 1,160, typically occurring at the end of the winter, and 30 cfs can be released when the lake level reaches EL 1,170. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-20 Supporting Design Report – FINAL 14 June 2012 Graph 3-2 Cooper Lake Temperature Profiles (2002-2003) Plotted on Average Historical Cooper Lake Levels Graph 3-3 Post-Construction Net Inflow to Cooper Lake versus Historical Lake Levels Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-21 Supporting Design Report – FINAL 14 June 2012 Graph 3-4 Post-Construction Target Discharge from Cooper Lake to Cooper Creek versus Historical Lake Levels 3.5.2.1.2 Siphon Inlet Structure Design of the Siphon Option inlet structure is controlled by vortexing /air entrainment. Using Gordon’s criteria for submergence to prevent vortex formation, the required depth over the top of the intake pipeline is about 3.8 feet for the design flow of 30 cfs and 1.3 feet for 10 cfs. 3.5.2.1.3 Siphon Outlet Design of the Siphon Option outlet is controlled by hydraulic losses in the pipeline and the maximum and minimum design flows. Hydraulic losses in the Siphon Option require the outlet to have an invert elevation of 1,153 feet. To achieve these elevations with the shortest length of pipe possible, the outlet is placed as far upstream along Cooper Creek as possible. For the Siphon Option this is in the creek bed immediately downstream of the dam. From the outlet structure, a channel to the desired elevation in the creek bed must be excavated. The size of the outlet structure is governed by the maximum and minimum design flows. The outlet structure is designed to accommodate the rough hydraulic profile at the minimum and maximum flows. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-22 Supporting Design Report – FINAL 14 June 2012 3.5.2.1.4 Flow Control and Monitoring Flow control for the Siphon Outlet will be set using a remotely-operable electric gate actuator, with a manual adjustment mechanism as a back-up. As with the Diversion Dam, the Cooper Lake Dam Outlet Works will be inaccessible during the winter, November through April, making manual adjustment difficult unless accessed by helicopter. During that time the required release from Cooper Lake is constant (10 cfs), except for a slightly higher flow requirement (15 cfs) in October. However, the lake level changes appreciably during that period. Similar to the Diversion Dam, if the control valve for the Siphon Outlet is fixed at the end of October for the winter, the flow through the outlet works will vary substantially. The varying discharge may be an unacceptable trade-off as it will reduce generation. Analysis of historical lake conditions indicated that automated adjustment capability would be required for efficient system operation. Flow monitoring will be as indicated in Section 3.6. 3.5.2.2 Geotechnical Design The soils underlying and adjacent to the siphon inlet are expected to consist of dense glacial outwash material. The soils underlying and adjacent to the siphon outlet are expected to primarily consist of fine-grained terminal moraine deposits. Foundation design parameters for the anticipated soil conditions at the location of the siphon inlet and outlet structures are presented in Table 3-8. Detailed calculations of foundation bearing capacities of the Siphon Outlet Works facilities are presented in Appendix B. Table 3-8 Diversion Outfall Foundation Design Parameters Siphon Foundation Design Parameter Design Value Siphon Inlet Structure (Glacial Outwash) Siphon Outlet Structure (Fine-Grained Moraine Deposits) Strip/Spread Bearing Capacity1 (psf) 3,500 psf 1,500 psf Slab on Grade Bearing Capacity 1,200 psf 500 psf Coefficient of Friction (Soil-Concrete Interface) 0.44 .40 Seismic Site Class C D 0.2 Second Seismic Coefficient (Ss)2 1.779 g 1.185 g 1.0 Second Seismic Coefficient (S1)2 0.660 g 0.660 g Notes: 1. Bearing Capacity estimated based on feasibility layout. Modifications to the feasibility may affect (increase or decrease) the allowable bearing capacity. 2. Ss and S1 are based on values for a Site Class B. These values were adjusted during design based on site class in accordance with the IBC (2006). Channels will be constructed leading up to the siphon’s inlet structure and leading away from the siphon’s outlet structure. The side slopes of these channels have been designed in accordance with data previously presented in Table 3-4. The slopes of the inlet channel and the base of the outlet channel are armored with revetments. The revetments were designed in accordance with Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-23 Supporting Design Report – FINAL 14 June 2012 the United States Army Corps of Engineers recommendations, or other acceptable guidelines. Design calculations for revetment are presented in Appendix B. 3.5.2.3 Structural Design The structural design of the Siphon Outlet and appurtenant structures has been designed in accordance with the codes, standards and applicable loadings indicated under Section 2 and the geotechnical design criteria indicated above. Supporting calculation for this structure are presented in Appendix B. The Siphon Inlet will be precast and will be designed by the manufacturer in accordance with the Project specifications. 3.5.2.3.1 Rupture Calculations The siphon pipe is subjected to up to 26 feet of shotrock fill over the crown of the pipe and an unusual water level to the crest of the spillway, 13 feet above the normal maximum lake level. In addition a vacuum of 12 psi has been calculated. The pipe was designed in accordance with AWWA M11 requirements and checked under the requirements of AISI Welded Steel Pipe, Vol. 3. A minimum wall thickness of 3/16-inch has been computed and 1/16-inch of corrosion allowance has been added. See Appendix B for calculations. 3.5.2.3.2 Traffic Load Calculations Vehicle access to the diversion access road will be routed over the siphon pipeline near the upstream portion of the existing Cooper Lake Dam Spillway. It was determined that the maximum load on the siphon pipeline was located approximately 250 feet downstream of this location at where the trench backfill above the pipe is about 29 feet deep. In comparison to the location of the deepest trench backfill, the location where the access road crosses the siphon pipe is approximately 7 feet shallower, resulting in a dead load variation of approximately 840 pounds per square foot. Considering that highway traffic loads are commonly modeled with a live load of 250 pounds per square inch, the portion of the siphon pipe that will be exposed to traffic loads was not considered critical. Accordingly, rupture calculations were based on the maximum trench loads and traffic loads were not considered. 3.5.2.3.3 Thrust Calculations The siphon pipeline is continuously welded and deeply buried. Thrust forces are taken by axial tension in the pipe and into the sides of the trench. 3.5.2.3.4 Concrete Cutoff Wall Calculations The concrete cutoff wall will be keyed into the trench side walls to provide the resistance necessary against lateral loading. The wall was designed for the design seismic event, with normal maximum operating water level at EL 1,194. Under normal conditions, backfill will be present on both sides of the wall. However during a flood, the possibility exists that backfill on the downstream side of the wall will be scoured out. Therefore, the cutoff wall will also be Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-24 Supporting Design Report – FINAL 14 June 2012 designed to resist full hydrostatic head and backfill on the upstream side only. See Appendix B for calculations. 3.5.3 Construction Construction of the Siphon Outlet Works will require a deep cut through the rock spillway at Cooper Lake Dam. During construction the reservoir will be lowered to the range of EL 1,160 to 1,165, if possible. Through the spillway the siphon pipeline will likely be installed by rock trenching methods through the spillway to a point downstream of the dam as shown on the Project drawings. The trench will likely be cut with a minimum width for efficient construction of the pipeline. The Project specifications require that the contract submit a plan for excavation and installation of the siphon in the active Cooper Lake Dam spillway. It is likely that the excavation will be performed in stages to allow the spillway and installed pipe to always be plugged/sealed against release of reservoir water. Trenching in soils upstream of the spillway will be required down to the lake level. Dredging or other means of underwater excavation will be required within the lake to the inlet structure. The outlet of the siphon will be constructed within the existing channel of Cooper Creek approximately 150 feet downstream of the dam. A siphon outlet trench will be constructed from the siphon outlet to a point where the diverted water will daylight at an approximate elevation of 1,150 feet. The outlet trench will be laid back at a slope of approximately 2H:1V to 2.5H:1V, depending on the soils encountered. The siphon trench is expected to encounter glacial outwash and till upstream of the spillway, slate within the spillway and colluvium overlying fine grains soil downstream of the spillway. Standard soil trenching approaches are anticipated within the soil portions of the siphon pipeline alignment. The pipeline within these portions of the siphon pipeline will be seated in granular pipe bedding and backfilled with select backfill placed as structural fill. Rock trenching methods, including controlled blasting, hydraulic rock breakers, or other rock excavation techniques will be required within the existing spillway. Both concrete and granular backfills will be used within the rock trench portion of the siphon excavation. A concrete cutoff wall will be constructed approximately in line with the centerline of the dam to help maintain the water-tightness. This wall will extend upward to match the current elevation of the existing spillway. Portions of the spillway weir that are removed as part of the planned work will not be replaced. Outside the limits of the existing spillway, the siphon will be backfilled with granular pipe bedding materials. The remainder of the rock trench will be backfilled with shotrock from rock excavations. It is likely that the Siphon could be completed in one season (May to October); however, there is also significant delay risk. Little interference is expected with the construction of the Diversion Dam and Diversion Pipeline, though access to the Diversion Pipeline right-of-way will require access across the upstream end of the spillway. Since the construction of the diversion dam and pipeline is likely to take place concurrently with the construction of the outlet facilities, project planning will be an essential part of completing the project without delays. Careful coordination between construction crews will be required in order to construct the siphon outlet without impairing the access to the diversion facilities. The Project Specifications will provide for the reservoir drawdown during the 2013 construction season. This allows for a contingency drawdown in 2014 if construction difficulties arise in 2013. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-25 Supporting Design Report – FINAL 14 June 2012 3.5.4 Maintenance Maintenance of the Cooper Lake Dam Outlet Works is expected to be periodic. As snow usually covers the area from November through April, it is expected that the Outlet Works will operate without maintenance during this period other than to periodically adjust the outlet gate. When the area thaws in May, Chugach staff will be able to access the facilities to maintain the gate, clean the trashrack, remove any debris on or near the inlet and outlet structures, and repair any damage that may have occurred over the winter. The sluice gate is expected to be DC electrically operated. Chugach staff will maintain the gates and valves throughout the spring and summer, and prepare the gates and valves for winter. Boats and hand rakes will be used to clean the trashracks. The inlet, outlet, and any exposed pipeline should be inspected for damage and the trashrack should be cleaned periodically from May to October. Flows will be periodically adjusted manually to meet the flow release regime specified in the Settlement Agreement or developed with the Interagency Committee. Before winter begins, Chugach staff will perform a final inspection of the Outlet Works, removing debris, cleaning the trashrack, and performing final repairs and maintenance. 3.6 INSTRUMENTATION 3.6.1 Feature Description In accordance with the Settlement Agreement flow measurement is required on the Stetson Creek Diversion flow and for flows released from Cooper Lake Dam to Cooper Creek. In addition, water temperatures are required to be monitored at the mouth of Cooper Creek. The flow in the Diversion Pipeline will be monitored by a flow meter located in a vault near the downstream end of the pipeline in a section of pipe that will always be flowing full. This location is at Diversion Pipeline STA 95+00+/- and requires creation of a short section of lowered pipe to ensure the pipe will always be flowing full. Flow in Cooper Lake Siphon Outlet Pipeline from Cooper Lake to Cooper Creek will be monitored by a flow meter installed in a vault at Siphon Pipe STA 16+00 upstream of the Siphon Outlet Structure. The two flow meters will be powered by off-line solar/wind power supplies with battery storage. Temperature monitoring at the mouth of Cooper Creek presently exists at the existing USGS Gaging Station No. 15261000, which provides water temperature information at 15-minute increments in accordance with the requirements of the Settlement Agreement. It is proposed that temperature information can be made available to Chugach via an agreement with USGS. Flow releases will be monitored and data recorded at least once every 15 minutes. The Settlement Agreement stipulates that Chugach must provide flow data for the flow release from Cooper Lake to Cooper Creek to the Interagency Committee on a quarterly basis. Recording and telemetry equipment will be provided at the Stetson Creek and Cooper Lake Bypass flow meter vaults using solar and wind power with a battery backup and UHF radio data transmission. Flow release at the Siphon Outlet Structure will be automatically maintained using an automated gate operator. The Siphon Outlet Structure Gate Control Panel (located within the Siphon Instrumentation Building) is designed to automatically control the flow through the outlet gate. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-26 Supporting Design Report – FINAL 14 June 2012 The siphon outlet gate will be provided with a motor operated controller that will automatically adjust the gate opening to maintain a fixed outlet flow. The flow set point will be manually entered at the Gate Control Panel. The Gate Control Panel will monitor siphon pipe flow and outlet gate position. Using these parameters the control panel will send signals to the siphon pipe gate controller to maintain proper flow. The control panel will also be designed to transmit flow and miscellaneous status and alarm information to the Monitoring Panel located within the Diversion Pipeline Instrumentation Building. Power for controlling the gate operator and control panel will be generated from a solar panel array and small wind generator, backed up by a storage battery. A screw type stem operator will be used to control the siphon pipe outlet gate position. The operator will be provided with a manual hand-wheel handle and a motorized gearbox for raising and lowering the gate. The hand-wheel will be provided with a clutch assembly for disengaging when using the motor operator. The motor operator will be powered by a 48VDC reversing motor. The operator will be provided with a local controller for either manual or motorized control at the gate and remote provisions for operation from the siphon control panel. The gate operator will provide signals to the Gate Control Panel indicating full open and full closed gate position, along with an analog signal indicating the gate position between 0-100%. The gate operator was designed for cold weather operation with an operating temperature range of -40ºC to +60ºC. 3.6.2 Design Information No outside power or data lines will be brought onto the site for instrumentation purposes. Accordingly, all instrumentation will be solar/wind powered, and data will be transferred to the existing Chugach SCADA system at the Cooper lake Powerhouse. Information transfer to the Cooper Lake Powerhouse will be via UHF radio. A UHF radio modem will be provided at the Diversion Pipeline Instrumentation Building. The information will be transmitted to the existing Chugach SCADA equipment located at the Cooper Lake Powerhouse. The flow meters will use ultrasonic transit-time measurement principles with two monitoring paths to determine flow. The flow sensors will be mounted on the outside of the pipe. A microprocessor type monitoring panel will process the sensor data and transmit a signal to the siphon control panel indicating pipe flow. Flow will be monitored locally at the flow monitoring panel and remotely at the Diversion Pipeline Instrumentation Building. The flow meter sensors will be installed in an underground vault and the monitoring panel will be installed in the instrument building near the outlet of each pipeline. The flow meters will be powered from the 24VDC power supply. A Gate Control Panel will be provided at the Siphon Instrumentation Building for automatically maintaining the siphon gate flow. The Gate Control Panel will be a Programmable Logic Controller (PLC) based controller containing components for monitoring the siphon pipe flow and gate position, and providing communication to the Diversion Pipeline Instrumentation Building Monitoring Panel data logger. The control panel will include the following systems: o PLC: The PLC system will process the flow, gate position, and flow set point information. Based on system status the PLC will send the proper signals to the outlet gate controller to maintain proper flow. The PLC will also monitor the Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-27 Supporting Design Report – FINAL 14 June 2012 power supply, flow meter, and gate motor operator and send critical alarm and status information to the radio modem. o OIT: The panel will include an operator interface terminal (OIT) on the panel cover to provide the following control and monitoring functions: Outlet gate position, 0-100% Outlet gate full open & full closed indication Siphon pipe flow, cfs Flow set point, cfs Power supply voltage Alarm indication for PLC, power supply, flow meter, and gate operator trouble A Monitoring Panel will be provided at the Diversion Pipeline Instrumentation Building for gathering pertinent data and transferring information to the Cooper Lake Powerhouse SCADA. The Monitoring Panel will be provided with a data logger to interface the analog and digital data with the UHF radio modem. An RS-232 output from the data logger will send information to the radio modem. A direct interface with the existing Chugach SCADA RTU at the Cooper Lake Powerhouse will be provided by the UHF radio modem. The following information will be available at the data logger via hardwire connections and a Modbus serial connection to the Siphon Instrumentation Building Gate Control Panel. o Dam #1 Float Well High o Dam #2 Float Well High o Dam #3 Float Well High o Diversion Pipeline flow o Diversion Flow Meter Trouble o Siphon Outlet Structure Flow o Siphon Outlet Structure Flow Meter Trouble o Siphon Outlet Gate Position o Siphon Outlet Gate Operating Mode o Siphon Outlet Flow Set point o Siphon Outlet Gate Operator Trouble o Siphon Outlet PLC Failure o Diversion Instrumentation Building Power Supply Voltage o Diversion Instrumentation Building Power Supply Trouble o Siphon Instrumentation Building Power Supply Voltage o Siphon Instrumentation Building Power Supply Trouble Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-28 Supporting Design Report – FINAL 14 June 2012 The power supply will be an off-grid type system using solar panels and wind generation to maintain charge on a storage battery. A storage battery will be located at each of the pipeline instrumentation buildings (24VDC at the Diversion Pipeline Instrumentation Building and 48VDC at the Siphon Instrumentation Building). The systems have been designed to carry 100% of the control system load (less motor operating power at the Siphon Instrumentation Building) using only the solar and wind generation. The siphon gate motor operator will require approximately 2000 Watts to run with a stating current of approximately 100 A. The Siphon Instrumentation Building battery will be sized to provide the required motor power on a short term basis, which will permit recharging the battery to full capacity between motor operations. Since the siphon head pressure will experience little variation on a daily to weekly basis it is anticipated that, at the most, the gate motor will run for very short periods possibly once or twice a week. With this type of load cycle there should not be a problem in keeping the battery at a full charge. Performance of the solar and wind generation is based on typical daylight and wind conditions. To account for abnormal conditions the battery is sized to power the control and monitoring systems for a period of 20 to 30 days without the charger in service. The battery will be provided with an insulated enclosure to optimize capacity. The battery and charging control components will be installed inside of the instrumentation buildings. The photo voltaic (PV) array and the wind generator will be installed on a pole structure located on the dam crest. Design calculations of the supporting pole structure are included in Appendix B. The PV array will be installed high enough to remain above the maximum snow line. The primary power supply components will include: o Three (3) 250 Watt (W), 31VDC PV modules o One (1) 1000W wind generator o Solar/Wind charge controller o Solar PV and wind generator mounting structure o Sealed gel batteries, 24V, and 48V Equipment specifications match the communication and power supply equipment presently being used by Chugach at the recently installed monitoring station at the Cooper Lake Dam crest. All equipment will be housed in NEMA 4X enclosures. All cable will be enclosed in galvanized steel conduit raceway, or otherwise protected from the elements and wildlife. 3.7 BORROW AREAS 3.7.1 Feature Description Two potential borrow sources were identified and explored during the first season of geotechnical work. The right abutment borrow source is located upstream of Cooper Lake Dam’s right abutment. The outfall borrow source is located along the shoreline of Cooper Lake from near the proposed outfall of the diversion pipeline to just south of the Cooper Lake Dam spillway. In later stages of design, the outfall borrow source was eliminated due to conflicts with the diversion access road and due to the relatively small volume of available material in comparison with the right abutment borrow source. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-29 Supporting Design Report – FINAL 14 June 2012 3.7.2 Design Information Both the right abutment and outfall borrow sources consist of medium dense to dense, course grained soil comprised of variable mixtures of sand, gravel, and cobbles. These sources contain occasional silty lenses and sporadic boulders. Groundwater of these borrow sources correspond closely with the elevation of Cooper Lake and is likely to fluctuate with the lake level. Aggregates from the borrow sources will be used for trench backfill and haul road surfacing. These aggregates may be used as concrete aggregates provided they meet the durability and Alkali-Silica Reaction (ASR) requirements for the concrete mix design. For completeness, Table 3-9 presents the estimated aggregate volume from both the right abutment and outfall borrow sources. Table 3-9: Anticipated Borrow Source Volume Borrow Source Volume (yd 3) Right Abutment Borrow Source 70,000 Outfall Borrow Source 9,500 Notes: 1. Volumes assume that water level is located at or below an elevation of 1,182 feet. A petrography test was conducted to determine the minerals that make up the borrow source aggregate. The petrography test indicated that the aggregate consists of calcareous, fine grained, deformed sandstone (slate). This is consistent with the host rock at the site. The results of the petrography test identify a number of minerals that are presented in Table 3-10. Table 3-10: Petrography Test Results Mineral Constituent Percentage of Total Constituents Calcite 50 Angular to subrounded strained detrital quartz 35 Feldspar = or < 6 Muscovite = or < 6 Sericite = or < 6 Opaques (Magnetite, ilmenite/leucoxene, or Hemitite) = or < 6 Other occasional Constituents = or < 6 Selected borrow source samples were tested for a suite of corrosion tests. The results of these tests are presented in Table 3-11. Stetson Creek Diversion and Cooper Lake Dam Facilities Page 3-30 Supporting Design Report – FINAL 14 June 2012 Table 3-11: Corrosion Testing Results Sample pH (pH units) Specific Conductivity (µS/cm) Chloride (mg/Kg) Sulfate (mg/Kg) Sulfide (mg/Kg) Oxidation- Reduction Potential (mV) Corrosivity (pH units)Test Pit Depth (ft) 4 2 5.84 ND ND ND ND 438.8 5.99 7 4 6.78 ND ND ND ND 390.0 6.98 8 2.5 6.18 ND ND ND ND 401.4 6.81 9 12.5 6.70 ND ND ND ND 391.4 6.80 Notes: µS/cm – microSiemens per centimeter ft – feet mg/Kg – milligrams per kilogram mV – millivolts ND – not detected APPENDIX A FERC Order on Offer of Settlement and Issuing New License APPENDIX B Calculations APPENDIX B – CALCULATIONS LIST OF CONTENTS B1 Hydraulics B2 Diversion Dam Bearing Capacity B3 Diversion Dam Abutment Stability B4 Diversion Dam and Intake – Structural B5 Diversion Dam – Adverse Rock Joint Sliding B6 Diversion Access Rock Cut – Kinematic Analysis B7 Spiral Nail Reinforced Slopes B8 Gabion Walls B9 Diversion Pipeline Buckling B10 Diversion Pipeline Miscellaneous B11 Diversion Pipeline Culvert Sizing B12 Diversion Pipeline Collar Weight B13 Diversion Outlet Structures – Bearing Capacity B14 Riprap Sizing and Filter B15 Siphon Outlet – Structural B16 Siphon Outlet Pipe Calculations B17 Siphon Cutoff Wall – Structural B18 Solar Panel Supports APPENDIX B1 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam Outlet PROJECT NUMBER: 1011304 PROJECT COMPONENT: Hydraulic Calculations CLIENT: Chugach Electrical Association PERFORMED BY: W. Moore CHECKED BY: J. Bartels DATE: 5/23/12 DATE: 5/23/2012 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: 1. Diversion Pipe Hydraulics 2. Diversion Pipe Outfal Hydraulics 3. Siphon Hydraulics 4. Diversion Dam and Intake Hydraulics CRITERIA: As noted herein. RESULT: As noted herein. Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B2 APPENDIX B3 APPENDIX B4 Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:1 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304Dimensions/PropertiesBottom of dam EL =1420.5ftTop of dam EL =1430ftHeight of dam =9.5ftTop width =2ftBottom width =13.5ftD/S Height =1ftNormal HW EL =1430ftFlood HW EL =1436.5ftFlood TW EL =1428.5ftThickness of Ice =0.7ftNormal HW w/ ice EL =1429.3ftDensity of water =62.4pcf [DBR 2.4.1]Density of concrete =150pcf [DBR 2.4.1]Friction coefficient =0.48[DBR 2.4.1]Cohesion =390psf [DBR 2.4.1]Peak Ground Acceleration =1.773g [DBR Table 33]Seismic coefficient =0.473g [EM 111022100 47.b]Restoring forcesFv d RMSW 12550 12.5 31875SW 27331 7.7 56206SW 32025 6.8 13669Fv =11906Rm =101750Resultant SW @ d =8.5ft Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:2 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304NormalUsualFv Fh d OTMLoadsSelfweight11906 8.5 101750Headwater2816 3.178917Uplift4001 9.0036013=79052816 56821ResultantResultant Fv =7905lbsd =7.19fte =0.44ftOK! Within middle thirdSlidingSliding force =2,816lbsResisting force =9,059lbsFS Sliding =3.2OK! FS > 2.0BearingBearing heel =700psfBearing toe =472psfOK!Length comp =13.5ft% compression =100FloatationFS =3.0OK! FS > 1.3 Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:3 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304Normal w/ iceUnusualFv Fh d OTMLoadsSelfweight11906 8.5 101750Headwater2434 2.947168Uplift3721 9.0033485Ice thrust2000 9.1718333=81864434 42763ResultantResultant Fv =8186lbsd =5.22fte =1.53ftOK! Within middle halfSlidingSliding force =4,434lbsResisting force =9,194lbsFS Sliding =2.1OK! FS > 1.25BearingBearing heel =195psfBearing toe =1,018psfOK!Length comp =13.5ft% compression =100FloatationFS =3.2OK! FS > 1.2 Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:4 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304FloodUnusualFv Fh d OTMLoadsSelfweight11906 8.5 101750Headwater6669 4.0827219Tailwater1997 2.67 5325Tailwater weight2068 3.16 6530Nappe811 12.50 10140Uplift9517 7.0667202Full uplift @ cracked base789 13.111033644804672 18986ResultantResultant Fv =4480lbsd =4.24fte =2.51ftOK! Within middle halfSlidingSliding force =4,672lbsResisting force =7,109lbsFS Sliding =1.5OK! FS > 1.25BearingBearing heel =psfBearing toe =705psfOK!Length comp =12.7ft% compression =94FloatationFS =1.6OK! FS > 1.20.79ft0.79ftiterative crack width touse =input width to equalabove => Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:5 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304MDEExtremeFv Fh d OTMLoadsSelfweight11906 8.5 101750Headwater2816 3.178917Uplift4001.4 9.0036013Westergaard1553 3.916077Seismic SW11206 5.256330Seismic SW23466 3.8313287Seismic SW3957 0.5047979059998 30648ResultantResultant Fv =7905lbsd =3.88fte =2.87ftSlidingSliding force =9,998lbsResisting force =8,331lbsFS Sliding =0.8BearingBearing heel =psfBearing toe =1,359psfLength comp =11.6ftCrack length =1.9ft% compression =86FloatationFS =3.0OK! Resultant withinbasePer the FERC, factor ofsafety underearthquake loadingneed not be evaluated Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:6 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304Post EarthquakeUsualFv Fh d OTMLoadsSelfweight11906 8.5 101750Headwater2816 3.178917Uplift3448 7.7526733Full uplift @ cracked base1108 12.571391973512816 52181ResultantResultant Fv =7351lbsd =7.10fte =0.35ftOK! Within middle thirdSlidingSliding force =2,816lbsResisting force =3,528lbsFS Sliding =1.3OK! FS > 1.0BearingBearing heel =629psfBearing toe =460psfOK!Length comp =13.5ft% compression =100FloatationFS =2.6OK! FS > 1.3 Description:Stetson CreekDiversion DamBy:BJBDate:6/7/2012Page:7 of7Client:ChugachChkd by:MBDate:6/7/2012Job Number:1011304ConstructionUnusualFv Fh d OTMLoadsSelfweight11906 8.5 101750ResultantResultant Fv =11906lbsd =8.55fte =1.80ftOK! Within middle halfBearingBearing heel =1,586psfBearing toe =178psfOK!Length comp =13.5ft% compression =100Construction w/ EQExtremeFv Fh d OTMLoadsSelfweight11906 8.5 101750Seismic SW11206 4.25 5124Seismic SW23466 3.83 13287Seismic SW3957 0.50 47911906 5629 120640ResultantResultant Fv =11906lbsd =10.13fte =3.38ftSlidingSliding force =5,629lbsResisting force =151,192lbsFS Sliding =26.9OK! FS > 1.1BearingBearing heel =2,357psfBearing toe =psfOK!Length comp =10.1ft% compression =75OK! Resultant withinbase APPENDIX B5 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam Outlet PROJECT NUMBER: 1011304 PROJECT COMPONENT: Diversion Dam CLIENT: Chugach Electrical Association PERFORMED BY: BJB CHECKED BY: PDR DATE: 6/11/12 DATE: 6/11/2012 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: Assessment sliding stability along rock joints assuming a hypothetical, through-going joint that is parallel to the base of the dam foundation. This assessment considers multiple load cases including normal, unusual, and extreme loading conditions. Extreme load cases include a post-earthquake (residual strength conditions) scenario. CRITERIA: Refer to Design Basis Report for design Criteria. RESULT: The results of the calculations indicate acceptable factors of safety for all load cases considered. See attached pages for results of specific load case evaluations. Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B6 APPENDIX B7 APPENDIX B8 APPENDIX B9 APPENDIX B10 APPENDIX B11 APPENDIX B12 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Diversion Pipeline Collars PROJECT NUMBER: 1011304 PROJECT COMPONENT: CLIENT: Chugach Electrical Association PERFORMED BY: BJB CHECKED BY: MB DATE: 6/11/12 DATE: 6/11/2012 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: These calculations determine the minimum collar weight, minimum concrete dimensions to aquire the required weight, and reinforcement required. CRITERIA: . Min weight must be 2600 lbs. Design concrete to ACI 318-05 RESULT: See drawing CV-0129 Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B13 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet Siphon Intake Vault: Calculations assume that there is no rock present below structure. This assumption is intended to be a conservative approach since is likely that rock is present near or at the base of the intake structure. Input Data 2-1-1 Geometry Width of footing : B 7 ft Depth of footing:D 6 ft Length of footing:Lf 14 ft Load inclination:m 0deg Contact Pressure;qapp 1050 psf 2-1-2 Soil Parameters 1. Glacial Outwash Water above ground surface Unit Weight:bf2 67.6 pcf Friction angle:2 36deg Cohesion:c2 0deg N1 21 Layer Thickness:D1 1000 feet Mobilized interface friction between footing and base (2/3 of friction angle): 1 24deg basefriction tan 1( ) basefriction 0.45 5/3/2012 1/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 1. Bearing Capacity Analysis was performed based on Structural Fill Using Meyerhof's Bearing Capacity Equation ( Foundation Analysis and Design, Joseph E. Bowles, Table 4-1 and 4-3) Nq e tan 2( )tan 45deg 2 2 2 Nc Nq 1( ) cot 2( ) N Nq 1( ) tan 1.4 2( ) Nq 38 Nc 51 N 44 Passive earth pressure coefficiednt: Kp Kp 1 sin 2( ) 1 sin 2( ) Kp 4 Shape, Depth and inclination Factors Shape Factor sc 1 0.2 Kp B Lf sq 1 2 0=if 1 0.1 Kp B Lf otherwise s sq sc 1.39 s 1.19 sq 1.19 Depth Factor dc 1 0.2 Kp D B dq 1 2 0=if 1 0.1 Kp D B otherwise 5/3/2012 2/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet d dq dc 1.34 dq 1.17 d 1.17 Inclination Factor ic 1 m 90deg 2 iq ic i 0 2 0=if 1 m 2 2 otherwise ic 1.00 iq 1.00 i 1.00 Ultimate bearing capacity qult c2 Nc sc dc bf2 D sq dq Nq 0.5 bf2 B N s d qult 35978 psf FS Calculation FS qult qapp FS 34 Allowable Bearing Capacity with FS = 3 qall qult 3 qall 11993 psf 5/3/2012 3/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 2. Settlement Calculation 1. Immediate Settlement Calculation Using Theory of Elasticity proposed by Timoshenko and Goodier(1951) n= number of contributing corners B'=least lateral diment of contributing area I1 and I2 = influence factors Es = elastic Modulus u= Poisson's ratio H=influence depth (H=5B) 1.1 Influence Depth Calculation H 5 B H 35 feet 1.2 Average Es Calculation From Foundation Analysis and Design , Joseph E. Bowles, Table 5-6 Using relationship between Es and N for sandy gravels with N>15 Es1 600 N1 6( )2000 Es1 18200 kPa From Foundation Analysis and Design , Joseph E. Bowles, Equation 5-16-d Esm D1 Es1 D1 Esm 18200 kPa Es Esm 20.88 psf Es 380016 psf 5/3/2012 4/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 1.3 Poisson's ratio From Foundation Analysis and Design , Joseph E. Bowles, Table 2-7 u 0.3 1.4 Number of contributing corners m 4 (center of fooring) 1.5 Influence factors From Foundation Analysis and Design , Joseph E. Bowles, Table 5-2 and Figure 5-7 I1 0.641 I2 0.031 If 0.7 1.6 Immediate Settlement Calculation From Foundation Analysis and Design , Joseph E. Bowles, Equation 5-16 and 5-16a B2 B 2 (center of footing) Sm qapp B2 1 u 2 Es I1 1 2u( ) I2 1 u If m Sm 0.016 feet S Sm 12 S 0.195 inch Total Settlement = S 0.195 inch 5/3/2012 5/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet References : Assume load is less than a block of concrete the with the same volume as the intack L = 14 ft W = 7ft Hconcrete = 7ft Volume = 686cf Unit weight = 150 pcf Weight = 102900 lbs Bearing Area = 98sf Bearing Pressure = 1050psf 5/3/2012 6/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 5/3/2012 7/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 5/3/2012 8/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet H/B' = 35/3.5 = 10 L/B = 14/7 = 2 D/B = 6/7 = 0.9 If = 0.7 (interpolated) 5/3/2012 9/10 By: PDR Checked by: KKP Siphon Intake Structure Bearing Capacity and Settlement Chugach Electric Stetson Creek Diversion and Cooper Lake Outlet 5/3/2012 10/10 APPENDIX B14 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam Outlet PROJECT NUMBER: 1011304 PROJECT COMPONENT: Siphon Outlet Riprap & Filter Blanket Sizing CLIENT: Chugach Electrical Association PERFORMED BY: Matthew Prociv CHECKED BY: Wade Moore DATE: 5/23/2012 DATE: 5/24/2012 REV. DATE BY CHECK NOTES 0 5/24/2012 MDP WPM Calculations acceptable. CALCULATION DESCRIPTION: Calculate riprap and filter blanket D50 sizes, gradations, and thicknesses. CRITERIA: USACE rip rap and filter blanket design via ASCE Manual 110, “Sediment Engineering Processes, Measurements, Modeling, and Practice.” . RESULT: The riprap and filter blanket calculations are acceptable. Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B15 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam PROJECT NUMBER: 1011304 PROJECT COMPONENT: Siphon Outlet Structure CLIENT: Chugach Electrical Association PERFORMED BY: BJB CHECKED BY: MB DATE: 5/25/12 DATE: 5/25/12 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: These calculations determine required thicknesses and rebar placement for the siphon outlet structure. CRITERIA: Refer to Design Basis Report for general structural criteria RESULT: See drawings Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B16 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam Outlet PROJECT NUMBER: 1011304 PROJECT COMPONENT: Siphon Pipe CLIENT: Chugach Electrical Association PERFORMED BY: D. Thompson CHECKED BY: B. Miskill DATE: 6/1/12 DATE: 6/1/12 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: Pipe design for the buried siphon outlet pipe through the existing Cooper Lake Dam spillway. CRITERIA: Buried steel pipe is designed in accordance with the requirements of American Water Works Association (AWWA) M11, Steel Pipe--A Guide for Design and Installation, Fourth Edition, 2004, and checked using American Iron and Steel Institute (AISI), Steel Plate Engineering Data - Volume 3, 1989. Criteria is per attached Input to AISI "Steel Water Pipe Design Software", Version 1.0, 1999. RESULT: 30" ID pipe, conforming to the requirements of ASTM A283, A572, A1011 or A1018, with a minimum yield strength of 42 ksi is required per the design. Minimum wall thickness will be 1/4" which has a 1/16" corrosion allowance (i.e., 3/16" wall required), even though the pipe will be coated with a 50 mil coating and lining. Stetson-Cooper Calc-Cover-Sheet.xls APPENDIX B17 Description:Stetson CreekSpillway cutoff wallBy:BJBDate:6/6/2012Page:1 of1Client:ChugachChkd by:MBDate:6/6/2012Job Number:1011304Ref: Dwg CV0134DimensionsKey width =2.0ftBottom EL =1178ftBottom Width =5.5ftTop EL =1207ftAssumed slope, 1:0.25ForcesELPressureWidthMu Vu1178 1810 7.5 20.4 10.9LF = 1.61180 1685 8.5 24.3 11.51182 1560 9.5 28.2 11.91184 1435 10.5 31.6 12.11186 1310 11.5 34.7 12.11188 1186 12.5 37.1 11.91190 1061 13.5 38.7 11.51192 936 14.5 39.4 10.91194 811 15.5 39.0 10.11196 686 16.5 37.4 9.11198 562 17.5 34.4 7.91200 437 18.5 29.9 6.51202 312 19.5 23.7 4.91204 187 20.5 15.7 3.11206 62 21.5 5.8 1.11207 0 22 0.0 0.0MomentRebar #7As =0.60sq.inSpacing =12inConcrete thickness =24inCover =4inMax Mu=39.4ft.KMn=50.5ft.KOKShearMax Vu=12.1KVn =22.3KOK APPENDIX B18 CALCULATIONS COVER SHEET 2353 130th Avenue N.E., Suite 200 Bellevue, WA 98005 OFFICE (425) 896-6900 / FAX (425) 602-4020 PROJECT NAME: Stetson Creek Diversion-Cooper Lake Dam PROJECT NUMBER: 1011304 PROJECT COMPONENT: Solar Panel Support CLIENT: Chugach Electrical Association PERFORMED BY: BJB CHECKED BY: MB DATE: 5/25/12 DATE: 5/25/12 REV. DATE BY CHECK NOTES CALCULATION DESCRIPTION: These calculations determine the required utility pole class and embedment to withstand design windloads. CRITERIA: Refer to Design Basis Report for general structural criteria RESULT: See drawings Use Class 6 Douglas-Fir utility pole, with 6' min embedment Stetson-Cooper Calc-Cover-Sheet.xls