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

Anderson Dam Seismic Retrofit Project Update Public Meeting – City of Morgan Hill| March 22, 2017 1

Santa Clara Valley Water District serves… 2 million people 15 cities 4,700 well owners San Francisco Bay Area 13 water retailers 2 Morgan Hill Public Meeting 3-22-2017

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 3 Morgan Hill Public Meeting 3-22-2017

Anderson Dam: Key to County Water Supply Total Countywide Storage: 169,000 Acre-Feet Almaden Calero Anderson: 90,000 Acre-Feet Chesbro Coyote Stevens Guadalupe Creek Lexington Vasona 4 Morgan Hill Public Meeting 3-22-2017 Uvas

Map of Gauge Locations in Coyote Watershed Coyote Creek Streamflow Gauge Anderson Dam Storage Gauge Anderson Reservoir Coyote Reservoir Rainfall Gauge Coyote Reservoir 5 Morgan Hill Public Meeting 3-22-2017

Coyote Reservoir Rainfall: November 1 – December 30, 2016 Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) 1 3 2.5 2 Rainfall (inches) 1.5 1 0.5 0 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 Date 6 Morgan Hill Public Meeting 3-22-2017

Anderson Reservoir Storage: Nov. 1 – Dec. 30, 2016 Note: Anderson Reservoir Actual Storage Level is solid blue line Anderson Reservoir Storage (ALERT gauge 1480) 2 120% 100,000 Reservoir Capacity (625.0 ft elev. / 91,373 af) Storage (acre-feet) 100% 80,000 80% Interim DSOD Restriction (599.5 ft elev. / 61,810 af) Percent Full 60,000 60% 40,000 40% Emergency Storage (20,000 af) 20,000 20% 0 0% 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 Date 7 Morgan Hill Public Meeting 3-22-2017

Coyote Creek Flows: November 1 – December 30, 2016 Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) 3 60 50 40 Flow (cfs) 30 Anderson Reservoir outlet release to Coyote Creek: 40 cfs – 50 cfs 20 10 0 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 Date 8 Morgan Hill Public Meeting 3-22-2017

1 Nov 1 to Dec 30, Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) 2016 3 2.5 2 Rainfall (inches) 1.5 1 0.5 Rainfall 0 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27 2 Anderson Reservoir Storage (ALERT gauge 1480) 120% 100,000 Reservoir Capacity (625.0 ft elev. / 91,373 af) 100% Anderson Dam 80,000 Storage (acre-feet) 80% Interim DSOD Restriction (599.5 ft elev. / 61,810 af) Storage Levels 60,000 60% (blue line) Percent Full 40,000 40% 20,000 20% 0 0% 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27 3 Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) 60 Coyote Creek Flows 50 Downstream of 40 Anderson Dam Flow (cfs) 30 Emergency Storage (20,000 af) 20 10 0 9 Footer 11/1 11/8 11/15 11/22 11/29 12/6 12/13 12/20 12/27

Coyote Reservoir Rainfall: January 1 – February 28, 2017 Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) 4 3 Preliminary – subject to revision 2.5 Rainfall (inches) 2 1.5 1 0.5 0 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 Date 10 Morgan Hill Public Meeting 3-22-2017

Anderson Reservoir Storage: Jan. 1 – Feb. 28, 2017 Note: Anderson Reservoir Actual Storage Level is solid blue line Anderson Reservoir Storage (ALERT gauge 1480) 5 120% 100,000 Reservoir Capacity (625.0 ft elev. / 91,373 af) 100% Storage (acre-feet) 80,000 Percent Full 80% Interim DSOD Restriction (599.5 ft elev. / 61,810 af) 60,000 60% 40,000 40% Emergency Storage (20,000 af) 20,000 20% Preliminary – subject to revision 0 0% 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 Date 11 Morgan Hill Public Meeting 3-22-2017

Coyote Creek Flows: January 1 – February 28, 2017 Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) 6 8000 Preliminary – subject to revision Anderson Reservoir spillway 7000 flows peak at above 7,000 cfs 6000 Anderson 5000 Flow (cfs) Reservoir 4000 outlet Anderson Reservoir outlet is closed on reopened 2/20 as spillway flows exceed 2,000 cfs 3000 Anderson Reservoir outlet on 2/24 opened 100% on 1/9 (~425 cfs) 2000 Anderson Reservoir begins to spill on 2/18 1000 0 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 Anderson Reservoir stops spilling on 2/28 Date 12 Morgan Hill Public Meeting 3-22-2017

4 Jan 1 to Feb 28, Coyote Reservoir Precipitation Gauge (ALERT gauge 6021) 3 2017 2.5 Rainfall (inches) 2 1.5 1 0.5 Rainfall 0 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 5 Anderson Reservoir Storage (ALERT gauge 1480) 120% Anderson Dam 100,000 Reservoir Capacity (625.0 ft elev. / 91,373 af) 100% Storage Levels 80,000 80% Interim DSOD Restriction (599.5 ft elev. / 61,810 af) Storage (acre-feet) (blue line) Percent Full 60,000 60% 40,000 40% Emergency Storage (20,000 af) 20,000 20% 0 0% 1/1 1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 6 Coyote Creek at Madrone Streamflow Gauge (ALERT gauge 5082) 8000 Coyote Creek Flows 6000 Downstream of Anderson Dam 4000 Flow (cfs) 2000 0 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 13 13 Footer

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): Approx. No. of days Anderson storage is Approximate date projected to storage falls Weather remain above below DSOD Outlook DSOD restriction restriction Wetter Spring 55 - 65 Early May 2017 35 – 45 Average Spring Mid-April 2017 30 – 40 Drier Spring Early April 2017 14 Morgan Hill Public Meeting 3-22-2017

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. 15 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 16 | | Morgan Hill Public Meeting 3-22-2017

Background and Project Overview 17 | Morgan Hill Public Meeting 3-22-2017

Seismic Activity in the Vicinity of Anderson Dam Seismic environment 1911 Calaveras (6.5) 1984 Morgan Hill (6.1) 1979 Coyote Lake (5.7) 1989 Loma Prieta (6.9) 18 | Morgan Hill Public Meeting 3-22-2017

Anderson Dam Historical Earthquake Impacts Embankments - Minor longitudinal cracking on dam crest 1984 Morgan Hill 1989 Loma Prieta Earthquake Earthquake magnitude 6.1 magnitude 6.9 19 | Morgan Hill Public Meeting 3-22-2017

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 20 | Morgan Hill Public Meeting 3-22-2017

Existing Embankment Cross-section Lower finer fill and alluvium predicted to liquefy during the maximum credible earthquake 21 | Morgan Hill Public Meeting 3-22-2017

Initial Project: Address Liquefaction 10 feet high cofferdam (drained reservoir) Upstream embankment buttress Downstream embankment buttress Existing outlet pipe 22 | Morgan Hill Public Meeting 3-22-2017

Original Project: Liquefaction, New Intake and Outlets, Spillway / Crest Modifications New sloping intake New High Level Outlet conduit Spillway modifications 10 feet high cofferdam (drained reservoir) New lower level conduit in Upstream embankment buttress tunnel Downstream embankment buttress Abandon existing outlet pipe 23 | Morgan Hill Public Meeting 3-22-2017