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1 Santa Clara Valley Water District File No.: Agenda Date: 4/28/2017 Item No.: 6. BOARD AGENDA MEMORANDUM SUBJECT: Discussion on the Anderson Dam Seismic Retrofit Project. RECOMMENDATION: A. Receive an Overview and Update on the project; and B. Direct District staff to identify and provide the City with information about additional actions the City can take to advocate for federal, state or regional funding for Anderson Dam. SUMMARY: The Anderson Dam Seismic Retrofit Project (Project) was initiated in 2012 and is currently in the Design Phase. The purpose of this agenda item is to present staff s recommended modification for Anderson Dam s seismic retrofit, and its associated impacts to the Project cost, schedule, and interim risk reduction measures. Project Background In 2011, the District completed a seismic study of Anderson Dam, which indicated that material at the base and foundation of the dam embankment would weaken due to liquefaction in a 7.25 magnitude earthquake (the maximum credible earthquake (MCE)) on the Calaveras Fault, located approximately 1.2 miles from the dam. Such an event could significantly deform the dam embankment, risking an uncontrolled release from Anderson Reservoir. The 2011 study also indicated that an MCE could trigger fault offset on the conditionally active Coyote Creek-Range Front fault zone located in the vicinity of the dam, which would damage the existing outlet pipe. The District initiated the Anderson Dam Seismic Retrofit Project in 2012 to address the seismic deficiencies at the dam. The Project s Planning Phase was completed in July The Design Phase was initiated soon thereafter. Since 2009, the District has operated Anderson Reservoir under a restricted water level (approved by DSOD) as an interim risk reduction measure while the Project is being designed. Potential Failure Modes/Dam Deficiencies Identified during Design Phase Santa Clara Valley Water District Page 1 of 4 Printed on 4/26/2017 powered by Legistar

2 File No.: Agenda Date: 4/28/2017 Item No.: 6. Based on extensive geotechnical and geologic investigations that have been performed on and around the dam in 2015 and 2016, additional dam deficiencies have been identified which include: In addition to the potential for dam slumping due to liquefaction of unstable materials below the dam foundation, dam failure could result from potential seepage and internal erosion caused by a fault rupture beneath Anderson Dam; Anderson Dam does not have a functional transition zone within the dam embankment that would prevent internal erosion of the dam core material. If a fault rupture event results in cracking of the core, erosion of the dam s core material could allow water from the reservoir to seep through the dam s core and embankment and cause internal erosion (known as piping) of the embankment, which could lead to catastrophic failure of the dam. The materials of the dam s upstream embankment are also susceptible to liquefaction during a maximum credible earthquake on the Calaveras Fault Modified Seismic Retrofit Project As a result of the investigations, in December 2016, staff presented a modified seismic retrofit Project approach to the District s Board of Directors that would replace most of the existing dam with embankments that will meet modern dam safety and performance standards. Much of the material from the existing dam would be reused in the embankment reconstruction. The size of the reconstructed dam would be similar to that of the existing dam. As depicted graphically in, the new dam cross-section would be a compacted, zoned embankment dam with a central impervious clay core. It would include both a triple-layer chimney and horizontal blanket filter/drain/transition zones and compacted gravel shells. These features would address the previously-described dam deficiencies. All the liquefiable material at the base and foundation of the dam would also be removed. Because of the extensive earthwork to dismantle and rebuild the dam, the reservoir would be drained through two consecutive winters of construction. A diversion structure and appropriate construction staging and sequencing are being planned to minimize downstream flooding risk during these winter seasons. A detailed plan for reservoir operation during construction would also be developed. Interim Risk Reduction Measures The District has re-evaluated the Interim Risk Reduction Measures (IRRMs) which have been in place at Anderson Dam since 2011, including the reservoir operating restriction. These include: Temporary Operations Restriction (El. 602 ft, 45 feet below the crest, allowing about 61,800 ac-ft of available storage in the Reservoir). Note that DSOD does not allow operational restrictions as a permanent means to provide dam safety. Completion of the Seismic Retrofit Project Updated Dam Break Analysis Updated Emergency Action Plan Tailwater Alarm System Impact to Project Cost and Schedule The more extensive embankment retrofit to fully remediate all dam safety deficiencies would double Santa Clara Valley Water District Page 2 of 4 Printed on 4/26/2017 powered by Legistar

3 File No.: Agenda Date: 4/28/2017 Item No.: 6. the total Project cost from $200M to $400M (2016 dollars). Staff estimates that completion of the design and environmental documentation efforts for the modified Project will extend the start of construction by two years, to spring Due to the extensive additional earthwork involved in the dam s reconstruction, the modified Project s construction duration is expected to increase from three years to four years. Advocacy for Increased Funding The Anderson Dam Seismic Retrofit Project has an estimated project cost of $400 million (2016 dollars). Consequently, the District is seeking a path for federal funding of the project (Attachment 2). There is an existing federal interest, as Anderson Dam is under the jurisdiction of the Federal Energy Regulatory Commission (FERC) because it has a hydroelectric facility. At the state level, Governor Brown s February 24, 2017 proposal for increased funding to address dam safety and bolster water infrastructure relies mainly on voter-approved bond funding through Propositions 84, 1E, and 1. The surface water storage funding in these bonds is focused mostly on projects in the Delta and the Central Valley, or on projects with direct benefits for Delta water conveyance. Existing state bond funding, without geographic criteria precluding projects in Santa Clara County, is very limited. Consequently, the District is seeking amendments AB 18 (E. Garcia) and SB 5 (de León), the parks and water bonds now moving through the Legislature, to qualify project funding for Anderson Dam through a program for the retrofit and repair of dams with seismic safety restrictions. The District urges the City of San José to use its influence with the legislative leadership and in the Governor s office to support the following bond amendments. 1. Adopt Language for Funding the Retrofit of Dams with Seismic Safety Restrictions AB 18 and SB 5: Funding is needed to address the retrofit of dams with seismic safety restrictions. The sum of $300 million should be available to the Department of Water Resources for grants to local or regional water supply agencies for the seismic retrofit and repair of dams and appurtenant structures, with active restrictions due to seismic safety, as determined by the Department of Water Resources. Next Steps The Project work to be performed in the next few years includes: 1. Public Outreach: One or two public meetings every year to inform the community on Project progress and changes to the Project work and schedule. 2. Thirty percent (30%) design completion - June Sixty percent (60%) design completion - March Draft Environmental Impact Report (EIR) released for public review - mid Ninety percent (90%) design completion - December 2018 Santa Clara Valley Water District Page 3 of 4 Printed on 4/26/2017 powered by Legistar

4 File No.: Agenda Date: 4/28/2017 Item No.: 6. FINANCIAL IMPACT: The modified Anderson Dam Seismic Retrofit Project is estimated to increase from $200M to $400M (2016 dollars). The revised Project cost will be reflected in the District s Fiscal Years Capital Improvement Program that will be presented to the Board of Directors for approval in May CEQA: The recommended action does not constitute a project under CEQA because it does not have a potential for resulting in direct or reasonably foreseeable indirect physical change in the environment. ATTACHMENTS: : PowerPoint Attachment 2: Federal Funding Request UNCLASSIFIED MANAGER: Katherine Oven, Santa Clara Valley Water District Page 4 of 4 Printed on 4/26/2017 powered by Legistar

5 Anderson Dam Seismic Retrofit Project Joint SCVWD/City of San Jose Meeting April 28, 2017 Pg. 1 of 11

6 Project Overview Anderson Dam Existing Configuration Spillway Outlet Pipe Dam Embankment Crest of Dam Joint SCVWD/City of San Jose Meeting Pg. 2 of 11

7 Project Overview Problem Definition Magnitude 7.2 Earthquake on the Calaveras Fault or M6.6 on the Coyote Creek Fault Embankment slumps up to 25 feet due to liquefaction of lower fine fill and alluvium Outlet conduit buckles up to 4 feet due to fault rupture on the Range Front Fault Changes in Regulatory Requirements (DSOD and FERC) Outlet works does not meet current emergency drawdown criteria Spillway undersized for Probable Maximum Flood Joint SCVWD/City of San Jose Meeting Pg. 3 of 11

8 2013 Project: Liquefaction, New Intake and Outlets, Spillway / Crest Modifications Spillway modifications New High Level Outlet conduit New sloping intake 10 feet high cofferdam (drained reservoir) New lower level conduit right abutment alignment Upstream embankment buttress Downstream embankment buttress Abandon existing outlet pipe Pg. 4 of 11 Joint SCVWD/City of San Jose Meeting

9 June 2016: Dam Failure by Fault Rupture X X X Shown: Mapped traces of Coyote Creek Fault X Joint SCVWD/City of San Jose Meeting X X X Pg. 5 of 11

10 2016 Modified Project Cross-Section: 2013 Recommended Project Cross-Section: 2016 Modified Project New Transition Zone New Filter & Transition Zones New Gravel Fill Core Core Remnant Bedrock New Gravel Fill Joint SCVWD/City of San Jose Meeting Pg. 6 of 11

11 2016 Modified Project Footprint Remnant dam clay core to remain Existing dam footprint Existing dam clay core Post Project dam footprint Joint SCVWD/City of San Jose Meeting Pg. 7 of 11

12 Retrofit Includes High-Level and Low-Level Outlets Max Water Surface EL 628 ft 10% of Storage 90% of Storage High-Level Outlet 12-ft diameter Dam Crest Spillway Invert Anderson Dam Cross-Section Low-Level Outlet 6-foot diameter 8 Joint SCVWD/City of San Jose Meeting Pg. 8 of 11

13 2016 Modified Project Construction Sequence Full Height Over Winter (El 647 ft) Interim EL (570 ft) Winter 1 Interim EL (570 ft) Winter 2 Complete Construction (El 656 ft) Year 1: Dewatering, Outlet Tunnel Construction Dry Season* Year 2: Lower Dam to Interim Height (El 570 ft) Dry Season Year 3: Lower Dam to remnant core; re-build to Interim Height (El 570 ft) Dry Season Year 4: Build Dam to Full Elevation (El 656 ft) Winter Year 4: Reservoir begins to re-fill * Dry Season = April to October Joint SCVWD/City of San Jose Meeting Pg. 9 of 11

14 Project Schedule We are here NEPA/CEQA/Permitting NEPA / CEQA / Permitting Design Design Legend Construction Original Baseline December, 2016 Construction through 2024 Joint SCVWD/City of San Jose Meeting Pg. 10 of 11

15 Summary 2016 Modified Project More extensive embankment retrofit Increases total cost of Project from $200M to $400M Start of Construction extended to 2020 Supported by dam regulators and Board of Consultants Pg. 11 of 11

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17 AD Anderson Dam Seismic Retrofit Project Request: Find a path for federal funding of the Anderson Dam Seismic Retrofit Project. This project currently has an estimate project cost of $400 million. There is an existing federal interest as Anderson Dam is a Federal Energy Regulatory Commission (FERC) project as it has a hydroelectric facility. Project Importance: The water district is undertaking the Anderson Dam Seismic Retrofit Project to ensure public safety and secure a reliable water supply today and for future generations. It is estimated that a magnitude 7.25 earthquake on the Calaveras Fault centered less than 2 km (1.25 miles) from the dam; or a magnitude 6.6 earthquake on the Coyote Creek Fault centered beneath the dam could result in significant damage, which could lead to dam failure and the uncontrolled release of water. To reduce this risk, since 2009, the water district has been operating Anderson Reservoir at a restricted water level. This restriction limits the reservoir s storage capacity to two thirds of its total volume. This reduction represents almost 20% of the total surface water storage capacity in the 9 other reservoirs owned and operated by the water district, thus severely limiting the water district s ability to capture and store water. New findings during the design phase of the project indicated that there is a potential of greater damage to the dam from a severe earthquake. The extent of the seismic retrofit work has expanded. In early January 2017, the water district decided to restrict the maximum water surface elevation in the reservoir by an additional 10 feet (to 58% of total reservoir capacity). To remove the restriction and ensure a safe and reliable facility, this retrofit project aims to fix the problems with Anderson Dam. A catastrophic failure of Anderson Dam is projected to have a devastating impact on residents, businesses, and transportation infrastructure reaching far beyond the immediate dam vicinity. The geographic area vulnerable is projected to be an average of 3 mile wide swath that extends 44 miles south of the dam through the City of Watsonville to Monterey Bay and north 34 miles along US 101, through downtown San Jose to San Francisco Bay. Project Description: The Santa Clara Valley Water District is engaged in a major project to retrofit and strengthen Anderson Dam so it can safely withstand a strong earthquake. The effort is known as the Anderson Dam Seismic Retrofit Project. Status: The project is a complex undertaking and is currently in the design phase. Construction is anticipated to begin in spring 2020 and will take approximately four years to complete. Project Location: Anderson Dam is located in Morgan Hill. Project Cost: We currently estimate that the project will cost $400 million. Of that total cost, 15 to 20 percent will be spent on planning, design, and environmental studies and documentation, and the remaining will be spent for construction. These cost estimates may change as the project progresses. Anderson Dam Attachment 2 Pg. 1 of 2

18 2016 Modified Project Cross-Section: Original Project Concept Cross-Section: 2016 Modified Project Morgan Hill Public Meeting Attachment 2 Pg. 2 of Santa Clara Valley Water District 03/2017