Retrofit Project Update Public Meeting City of Morgan Hill| March - - PowerPoint PPT Presentation

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Anderson Dam Seismic Retrofit Project Update

Public Meeting – City of Morgan Hill| March 22, 2017

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Santa Clara Valley Water District serves…

2 million people 15 cities 4,700 well owners 13 water retailers

San Francisco Bay Area

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Water Supply from Imported Sources and Local Reservoirs Intricately Connected in County

10 reservoirs 3 pump stations 142 miles of pipelines 3 water treatment plants 1 advanced purification plant 393 acres of recharge ponds 275 miles of jurisdictional streams

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Anderson Dam: Key to County Water Supply

Anderson: 90,000 Acre-Feet

Lexington Guadalupe Coyote Chesbro Calero Almaden Stevens Creek Uvas Vasona

Total Countywide Storage: 169,000 Acre-Feet

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Map of Gauge Locations in Coyote Watershed

Anderson Reservoir Coyote Reservoir

Coyote Creek Streamflow Gauge Anderson Dam Storage Gauge Coyote Reservoir Rainfall Gauge

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Coyote Reservoir Rainfall: November 1 – December 30, 2016

0.5 1 1.5 2 2.5 3 11/1 11/3 11/5 11/7 11/9 11/11 11/13 11/15 11/17 11/19 11/21 11/23 11/25 11/27 11/29 12/1 12/3 12/5 12/7 12/9 12/11 12/13 12/15 12/17 12/19 12/21 12/23 12/25 12/27 12/29 12/31

Rainfall (inches) Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) Date

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Anderson Reservoir Storage: Nov. 1 – Dec. 30, 2016

0% 20% 40% 60% 80% 100% 120% 20,000 40,000 60,000 80,000 100,000 11/1 11/3 11/5 11/7 11/9 11/11 11/13 11/15 11/17 11/19 11/21 11/23 11/25 11/27 11/29 12/1 12/3 12/5 12/7 12/9 12/11 12/13 12/15 12/17 12/19 12/21 12/23 12/25 12/27 12/29 12/31

Percent Full Storage (acre-feet) Anderson Reservoir Storage (ALERT gauge 1480)

Reservoir Capacity (625.0 ft elev. / 91,373 af) Interim DSOD Restriction (599.5 ft elev. / 61,810 af)

Date

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Emergency Storage (20,000 af)

Note: Anderson Reservoir Actual Storage Level is solid blue line

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Coyote Creek Flows: November 1 – December 30, 2016

10 20 30 40 50 60 11/1 11/3 11/5 11/7 11/9 11/11 11/13 11/15 11/17 11/19 11/21 11/23 11/25 11/27 11/29 12/1 12/3 12/5 12/7 12/9 12/11 12/13 12/15 12/17 12/19 12/21 12/23 12/25 12/27 12/29 12/31

Flow (cfs) Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) Date

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Anderson Reservoir outlet release to Coyote Creek: 40 cfs – 50 cfs

9 Footer

0.5 1 1.5 2 2.5 3 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27

Rainfall (inches)

Coyote Reservoir Precipitation Gauge (ALERT gauge 6021)

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0% 20% 40% 60% 80% 100% 120% 20,000 40,000 60,000 80,000 100,000 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27

Percent Full Storage (acre-feet)

Anderson Reservoir Storage (ALERT gauge 1480)

Reservoir Capacity (625.0 ft elev. / 91,373 af) Interim DSOD Restriction (599.5 ft elev. / 61,810 af)

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Nov 1 to Dec 30, 2016

Emergency Storage (20,000 af)

Rainfall Coyote Creek Flows Downstream of Anderson Dam Anderson Dam Storage Levels (blue line)

10 20 30 40 50 60 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27

Flow (cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)

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Coyote Reservoir Rainfall: January 1 – February 28, 2017

0.5 1 1.5 2 2.5 3 1/1 1/3 1/5 1/7 1/9 1/11 1/13 1/15 1/17 1/19 1/21 1/23 1/25 1/27 1/29 1/31 2/2 2/4 2/6 2/8 2/10 2/12 2/14 2/16 2/18 2/20 2/22 2/24 2/26 2/28

Rainfall (inches) Coyote Reservoir Precipitation Gauge (ALERT gauge 6021)

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Date

Preliminary – subject to revision

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Anderson Reservoir Storage: Jan. 1 – Feb. 28, 2017

0% 20% 40% 60% 80% 100% 120% 20,000 40,000 60,000 80,000 100,000 1/1 1/3 1/5 1/7 1/9 1/11 1/13 1/15 1/17 1/19 1/21 1/23 1/25 1/27 1/29 1/31 2/2 2/4 2/6 2/8 2/10 2/12 2/14 2/16 2/18 2/20 2/22 2/24 2/26 2/28

Percent Full Storage (acre-feet) Anderson Reservoir Storage (ALERT gauge 1480)

Interim DSOD Restriction (599.5 ft elev. / 61,810 af) Emergency Storage (20,000 af) Reservoir Capacity (625.0 ft elev. / 91,373 af)

Date

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Preliminary – subject to revision

Note: Anderson Reservoir Actual Storage Level is solid blue line

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Coyote Creek Flows: January 1 – February 28, 2017

1000 2000 3000 4000 5000 6000 7000 8000 1/1 1/3 1/5 1/7 1/9 1/11 1/13 1/15 1/17 1/19 1/21 1/23 1/25 1/27 1/29 1/31 2/2 2/4 2/6 2/8 2/10 2/12 2/14 2/16 2/18 2/20 2/22 2/24 2/26 2/28

Flow (cfs) Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) Date

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Anderson Reservoir outlet

• pened 100% on 1/9 (~425 cfs)

Anderson Reservoir begins to spill on 2/18 Anderson Reservoir outlet is closed on 2/20 as spillway flows exceed 2,000 cfs Anderson Reservoir spillway flows peak at above 7,000 cfs Anderson Reservoir

• utlet

reopened

• n 2/24

Anderson Reservoir stops spilling on 2/28

Preliminary – subject to revision

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0.5 1 1.5 2 2.5 3 1/1 1/3 1/5 1/7 1/9 1/11 1/13 1/15 1/17 1/19 1/21 1/23 1/25 1/27 1/29 1/31 2/2 2/4 2/6 2/8 2/10 2/12 2/14 2/16 2/18 2/20 2/22 2/24 2/26 2/28

Rainfall (inches)

Coyote Reservoir Precipitation Gauge (ALERT gauge 6021)

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0% 20% 40% 60% 80% 100% 120% 20,000 40,000 60,000 80,000 100,000 1/1 1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26

Percent Full Storage (acre-feet)

Anderson Reservoir Storage (ALERT gauge 1480)

Interim DSOD Restriction (599.5 ft elev. / 61,810 af) Emergency Storage (20,000 af)

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Coyote Creek Flows Downstream of Anderson Dam

Reservoir Capacity (625.0 ft elev. / 91,373 af)

Jan 1 to Feb 28, 2017

Rainfall Anderson Dam Storage Levels (blue line)

2000 4000 6000 8000 1/1 1/3 1/5 1/7 1/9 1/11 1/13 1/15 1/17 1/19 1/21 1/23 1/25 1/27 1/29 1/31 2/2 2/4 2/6 2/8 2/10 2/12 2/14 2/16 2/18 2/20 2/22 2/24 2/26 2/28

Flow (cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)

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Anderson Dam Operations – Spring 2017

Estimate of timelines to draw down Anderson Reservoir to restricted level (presented to Morgan Hill City Council

• n March 15, 2017):

Weather Outlook

• Approx. No. of

days Anderson storage is projected to remain above DSOD restriction Approximate date storage falls below DSOD restriction Wetter Spring 55 - 65 Early May 2017 Average Spring 35 – 45 Mid-April 2017 Drier Spring 30 – 40 Early April 2017

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Summary

• Water District fully opened Anderson outlet valve
• n January 9, 2017.
• Water District continued releasing maximum

discharge from Anderson Reservoir until February 20, 2017.

• Outlet valve was fully re-opened on February 24.
• As of March 15th, Anderson Reservoir is 90% full.

It may take an estimated 30 – 65 days to return to restricted level.

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Meeting Purpose

► Objectives

► Provide the latest information on the seismic findings

and a modified project approach, an update on project status and schedule, and topics related to dam safety performance

► Address community questions and concerns ► Reinforce our commitment to public safety and

keeping the community informed as the project progresses ► Questions & Answers ► Informational Booths

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Background and Project Overview

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Seismic Activity in the Vicinity of Anderson Dam

Seismic environment

1989 Loma Prieta (6.9) 1979 Coyote Lake (5.7) 1984 Morgan Hill (6.1) 1911 Calaveras (6.5)

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Anderson Dam Historical Earthquake Impacts

1989 Loma Prieta Earthquake magnitude 6.9

Embankments - Minor longitudinal cracking on dam crest

1984 Morgan Hill Earthquake magnitude 6.1

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Problem Definition

► Magnitude 7.2 Earthquake on the Calaveras Fault

• r 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

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Existing Embankment Cross-section

Lower finer fill and alluvium predicted to liquefy during the maximum credible earthquake

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Initial Project: Address Liquefaction

10 feet high cofferdam (drained reservoir) Upstream embankment buttress Downstream embankment buttress

Existing outlet pipe

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Original Project: Liquefaction, New Intake and Outlets, Spillway / Crest Modifications

New sloping intake 10 feet high cofferdam (drained reservoir) Spillway modifications New High Level Outlet conduit Upstream embankment buttress Downstream embankment buttress New lower level conduit in tunnel

Abandon existing

• utlet pipe

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New Findings

X X X X X X X

Shown: Mapped traces of Coyote Creek Fault

X

Zone 1 Liquefaction

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Dam Failure by Fault Rupture

►

Key Findings

►

Downstream transition zone not functional

►

Impermeable core of the dam may crack

►

Seepage (piping) may occur

CRACK

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2016 Modified Project

► More Extensive Embankment Retrofit and

Additional Elements

►

Retrofitted embankment similar footprint to existing dam.

►

Remove all liquefiable material (compared to previous buttress approach)

► Other project elements remain unchanged

►

New high level and low level outlet

►

Spillway wall raise

►

Temporary cofferdam

►

New sloping intake

►

Crest raise for additional freeboard

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2016 Modified Project

Cross-Section: Original Project Concept Cross-Section: 2016 Modified Project

“ “

“ “

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2016 Modified Project Footprint

Existing dam clay core Remnant dam clay core to remain Post Project dam footprint Existing dam footprint

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2016 Modified Project Construction Sequence

Year 1:

Lower Dam to Interim Height (El 570 ft) Lower Dam to remnant core; re-build to Interim Height (El 570 ft)

Dry Season* Year 2: Dry Season Year 3: Dry Season Year 4: Winter Year 4:

Reservoir begins to re-fill Full Height Over Winter (El 647 ft) Interim EL (570 ft) Winter 1 Interim EL (570 ft) Winter 2 Complete Construction (El 656 ft) Build Dam to Full Elevation (El 656 ft) Dewatering, Outlet Tunnel Construction

* Dry Season = April to October

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Project Cost and Schedule

2017 2018 2019 2013 2014 2015 2016

We are here

2020

NEPA / CEQA / Permitting Design Construction 20202024

2021 2022

Project Cost:

► Modified Project Cost ~ $400M

Project Schedule:

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Morgan Hill Public Meeting 3-22-2017

Next Steps and Public Meetings

► 30% Design – June 2017 ► 60% Design – December 2017

► Public meeting in early 2018

► Draft Environmental Impact Report (EIR) for Public

Review – Summer 2018

► A public meeting for Draft EIR in late summer 2018

► 90% Design – September 2018

► Pre-construction meetings in 2019-2020

► Start of Construction - 2020

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Stay Informed

http://www.valleywater.org/Services/AndersonDamAnd Reservoir.aspx

► Sign up to receive project updates via email. ► View project reports, maps, history and other

information.

► Coming later in 2017: project blog

Peggy Lam

plam@valleywater.org (408) 630-2710

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Special Status Plants

Tiburon Paintbrush Coyote Ceanothus

• Mt. Hamilton Thistle
• S. Clara Valley Dudleya

Smooth Lessingia Metcalf Canyon Jewel-flower

Special Status Animals

California Red-Legged Frog Dusky Footed Woodrat Western Pond Turtle California Tiger Salamander

Anderson Geotechnical Investigations