anderson dam seismic retrofit project update · · 2018-02-05anderson dam reservoir capacity ......

1

Anderson Dam Seismic

Retrofit Project Update

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

22 Morgan Hill Public Meeting 3-22-2017

Santa Clara Valley Water District serves…

2 million people

15 cities

4,700 well owners

13 water retailers

San Francisco Bay

Area


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


Anderson Dam: Key to County Water Supply

Anderson: 90,000 Acre-Feet

Lexington

Guadalupe

Coyote

Chesbro

CaleroAlmaden

Stevens Creek

UvasVasona

Total Countywide Storage: 169,000 Acre-Feet


Map of Gauge Locations in Coyote Watershed

Anderson Reservoir

Coyote Reservoir

Coyote Creek Streamflow Gauge

Anderson Dam Storage Gauge

Coyote Reservoir Rainfall Gauge


Coyote Reservoir Rainfall: November 1 – December 30, 2016

0

0.5

1

1.5

2

2.5

3

11

/1

11

/3

11

/5

11

/7

11/9

11/1

1

11/1

3

11/1

5

11/1

7

11/1

9

11/2

1

11/2

3

11/2

5

11/2

7

11/2

9

12

/1

12

/3

12

/5

12

/7

12

/9

12/1

1

12/1

3

12/1

5

12/1

7

12/1

9

12/2

1

12/2

3

12/2

5

12/2

7

12/2

9

12/3

1

Rai

nfa

ll (i

nch

es)

Coyote Reservoir Precipitation Gauge (ALERT gauge 6021)

Date

1


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

0%

20%

40%

60%

80%

100%

120%

0

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

Perc

ent

Full

Sto

rage

(ac

re-f

eet)

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

2

Emergency Storage (20,000 af)

Note: Anderson Reservoir Actual Storage Level is solid blue line


Coyote Creek Flows: November 1 – December 30, 2016

0

10

20

30

40

50

60

11

/1

11

/3

11

/5

11

/7

11

/9

11/1

1

11/1

3

11/1

5

11/1

7

11/1

9

11/2

1

11/2

3

11/2

5

11/2

7

11/2

9

12

/1

12

/3

12

/5

12

/7

12

/9

12/1

1

12/1

3

12/1

5

12/1

7

12/1

9

12/2

1

12/2

3

12/2

5

12/2

7

12/2

9

12/3

1

Flo

w (

cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)

Date

3

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

99 Footer

0

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

Rai

nfa

ll (i

nch

es)

Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) 1

0%

20%

40%

60%

80%

100%

120%

0

20,000

40,000

60,000

80,000

100,000

11/1

11/8

11/1

5

11/2

2

11/2

9

12/6

12/1

3

12/2

0

12/2

7

Per

cen

t Fu

ll

Sto

rage

(ac

re-f

eet)Anderson Reservoir Storage (ALERT gauge 1480)



2

Nov 1 to Dec 30,

2016


Rainfall

Coyote Creek FlowsDownstream ofAnderson Dam

Anderson DamStorage Levels(blue line)

0

10

20

30

40

50

60

11/1

11/8

11/1

5

11/2

2

11/2

9

12/6

12/1

3

12/2

0

12/2

7

Flo

w (

cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)3


Coyote Reservoir Rainfall: January 1 – February 28, 2017

0

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

Rai

nfa

ll (i

nch

es)


Date

Preliminary – subject to revision


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

0%

20%

40%

60%

80%

100%

120%

0

20,000

40,000

60,000

80,000

100,000

1/1

1/3

1/5

1/7

1/9

1/1

1

1/1

3

1/1

5

1/17

1/1

9

1/2

1

1/2

3

1/2

5

1/2

7

1/2

9

1/3

1

2/2

2/4

2/6 2/8

2/1

0

2/1

2

2/1

4

2/1

6

2/1

8

2/2

0

2/2

2

2/2

4

2/2

6

2/2

8

Perc

ent

Full

Sto

rage

(ac

re-f

eet)





Date

5


Note: Anderson Reservoir Actual Storage Level is solid blue line


Coyote Creek Flows: January 1 – February 28, 2017

0

1000

2000

3000

4000

5000

6000

7000

8000

1/1

1/3

1/5

1/7

1/9

1/1

1

1/1

3

1/1

5

1/1

7

1/1

9

1/2

1

1/2

3

1/2

5

1/2

7

1/2

9

1/3

1

2/2

2/4

2/6

2/8

2/1

0

2/1

2

2/1

4

2/1

6

2/1

8

2/2

0

2/2

2

2/2

4

2/26

2/2

8

Flo

w (

cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)

Date

6

Anderson Reservoir outlet opened 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

outlet reopened

on 2/24

Anderson Reservoir stops spilling on 2/28


1313 Footer

0

0.5

1

1.5

2

2.5

3

1/1

1/3

1/5

1/7

1/9

1/11

1/13

1/1

5

1/1

7

1/1

9

1/2

1

1/2

3

1/2

5

1/2

7

1/2

9

1/3

1

2/2

2/4

2/6

2/8

2/1

0

2/1

2

2/1

4

2/1

6

2/1

8

2/2

0

2/2

2

2/2

4

2/26

2/2

8

Rai

nfa

ll (i

nch

es)


0%

20%

40%

60%

80%

100%

120%

0

20,000

40,000

60,000

80,000

100,0001

/1

1/8

1/1

5

1/2

2

1/2

9

2/5

2/1

2

2/1

9

2/26

Per

cen

t Fu

ll

Sto

rage

(ac

re-f

eet)




5

Coyote Creek FlowsDownstream of Anderson Dam


Jan 1 to Feb 28,

2017

Rainfall

Anderson DamStorage Levels(blue line)

0

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

Flo

w (

cfs)

Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082)6


Anderson Dam Operations – Spring 2017

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


Summary

• Water District fully opened Anderson outlet valve on 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.

16 | Morgan Hill Public Meeting 3-22-2017

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

|


Background and Project Overview


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)


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


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


Existing Embankment Cross-section

Lower finer fill and alluvium predicted to liquefy during

the maximum credible earthquake


Initial Project: Address Liquefaction

10 feet high cofferdam

(drained reservoir)

Upstream embankment buttress

Downstream embankment buttress

Existing outlet pipe


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

outlet pipe


New Findings

XX

X

X

XX

X

Shown:

Mapped traces of

Coyote Creek Fault

XZone 1 Liquefaction


Dam Failure by Fault Rupture

► Key Findings

► Downstream transition zone not functional

► Impermeable core of the dam may crack

► Seepage (piping) may occur

CRACK


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


2016 Modified Project

Cross-Section: Original Project Concept

Cross-Section: 2016 Modified Project

“ ““ “


2016 Modified Project Footprint

Existing dam clay core

Remnant dam clay

core to remain

Post Project dam

footprint

Existing dam footprint


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, OutletTunnel Construction

* Dry Season = April to October


Project Cost and Schedule

2017 2018 20192013 2014 2015 2016

We are here

2020

NEPA / CEQA / Permitting

Design

Construction 20202024

2021 2022

Project Cost:

► Modified Project Cost ~ $400M

Project Schedule:


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

|


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 [email protected]

(408) 630-2710

http://www.valleywater.org/Services/AndersonDamAndReservoir.aspx

mailto:[email protected]

Special Status Plants

Tiburon PaintbrushCoyote Ceanothus Mt. Hamilton Thistle

S. Clara Valley DudleyaSmooth Lessingia

Metcalf Canyon Jewel-flower

Special Status Animals

California Red-Legged Frog

Dusky Footed Woodrat

Western Pond Turtle

California Tiger Salamander

Anderson Geotechnical Investigations

anderson dam seismic retrofit project update · · 2018-02-05anderson dam reservoir capacity ......

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