C A L I F O R N I A D E P A R T M E N T O F W A T E R R E S O U R C E S
Jamie Anderson, Ph.D., P.E. California Extreme Precipitation Symposium
DWR Delta Modeling Section June 2019
Exploring Flooding and Water Supply Risks from Sea Level Rise in the Delta
Delta Flooding and Water Supply Risks from Sea Level Rise
Background Projections Research Take Home Messages
Vital to Economy
• 2/3 of Californians rely on Delta water
• Los Angeles, San Diego, Silicon Valley, Contra Costa depend on Delta water
• 3 million of acres irrigated with Delta water
• Delta water supports about $400 billion of the California economy
Vital to Environment
• 80% of the state's commercial fish species live in or migrate through the Delta
• The Delta is home to over 700 species of plants and animals
• Several threatened or endangered species
Green Sturgeon
White Sturgeon
Delta Smelt
Splittail
Longfin Smelt
Greater Sandhill Crane
Tri-Colored Blackbird
Giant Garter Snake
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64
12
205
160
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5 Hi-Voltage Lines
100s Gas Lines
3 Railroads3 Highways
160,000 Homes
Delta People and Infrastructure
The Delta is a maze of channels that flow into San Francisco Bay
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Largest freshwater inflow: Sacramento River2nd Largest freshwater inflow: San Joaquin RiverTidal flows from San Francisco Bay/OceanWater pumped out of the South Delta
River flows PUSH salt towards SF Bay
Water is PUMPED out of
the Delta
Tidal flows SLOSH
water and salt back and forth
Delta flows and water quality are a combination of natural processes (e.g. tides) and human decisions (e.g. reservoir releases)
Delta Islands
7Image from Dave Mraz, DWR
are bowls
Bradford Island
Delta islands are below sea level
1100 miles of levees protect Delta islands from rivers whose water levels are above the island ground levels
Delta Flooding and Water Supply Risks from Sea Level Rise
Background Projections Research Take Home Messages
1989 Projections
5.6ft
What has changed since 1989?
• Sea level rise projections are higher
• Identified Delta impacts are the same– Levees
• Increased pressure on levees• Overtopping and flood risk
– Salt water intrusion– Managing reservoirs for water quality
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Ocean Protection Council Sea-Level Rise Guidance (2018)San Francisco
Medium - High Risk Aversion (RCP 8.5) Extreme Risk Aversion (H++)
The California Ocean Protection Council (OPR 2018) and the Governor's Office of Planning and Research recommend: • select sea-level rise projections based on risk tolerance• analysis should consider climate impacts throughout the intended lifespan of the project• If flooding consequences are severe and there is a low ability to adapt, the Medium - High and Extreme Risk Aversion
scenarios provide a time horizon to guide adaptation planning
Sources: Ocean Protection Council. (2018). State of California Sea-Level Rise Guidance: 2018 Update. Retrieved from Ocean Protection Council website: http://www.opc.ca.gov/webmaster/ftp/pdf/agenda_items/20180314/Item3_Exhibit-A_OPC_SLR_Guidance-rd3.pdf ; Governor’s Office of Planning and Research (OPR). 2018. Planning and Investing for a Resilient California. http://opr.ca.gov/docs/20180313-Building_a_Resilient_CA.pdf
Slide created by Delta Stewardship Council, adaptation by Jamie Anderson DWR
1 ft
7 ft
6 ft3 ft
Projections are available for Median, Likely (middle 2/3rds of projections), 1 in 20 (5%)Medium High (0.5%), and Extreme (rapid loss of West Antarctica ice)
Storm surge will increase impacts
From R. Flick
Photo by Rob Duvall Jan 1, 2006 Sherman Island
Delta Flooding and Water Supply Risks from Sea Level Rise
Background Projections Research Take Home Messages
Subsidence of Levees Sacramento-San Joaquin Delta
• High subsidence rates for some of the levees in the Delta:~0.4 to 0.8 inches per year.
• Subsidence + SLR + storms could cause overtopping or failure of the levees.– Could expose natural gas
pipelines and other infrastructure to damage or structural failure.
• At this rate of subsidence, levees may fail to meet the federal levee height standard between 2050-2080.
Brooks et al., 2018http://www.climateassessment.ca.gov/techreports/energy.html
Land Elevations
Levee Freeboard
Subsidence
SLR
SLR = Sea Level Rise
Delta water levels flood & sea level riseSan Joaquin River
Areas where water surface elevations exceed top of levee elevation
Maendly, 2018 http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-011.pdf
Levee crest elevation 10 year or 200 year flood, 1.27 ft sea level rise
During extreme floods, climate change hydrology has biggest impact
Impacts of climate change and sea level rise on water supply studyKey Assumptions• Current water project operating rules
– Includes 2008 & 2009 Biological Opinions– Current Delta water quality standards (X2)
• Water demands based on an estimated 2015 level of development
• Poster Session: Addressing Uncertainties in Climate Change Assessments by Jay Wang
Wang et al., 2018 http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-004.pdf
Mean Impact on Delta OutflowNet Delta Outflow increases significantly in the winter and early spring and decreases in late spring and summer
Increases in winter & early spring
Decreases in late spring & summer
Basin inflows increase in winter
Runoff shifts earlier in spring
Wang et al., 2018 http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-004.pdf
Sacramento Basin Inflows Upstream of Reservoirs
Net Delta Outflow
Salinity Intrusion from Sea Level Rise
• Increased salinity intrusion
• Need increased freshwater inflows to maintain water quality
• Impacts water supply and ecosystems
Tides
MorePUSH
Needed
SLOSH + More SALT More
PUSH NeededAffects
PUMPING
Salinity IntrusionX2 (km from Golden Gate with salinity of 2ppt)
Deltarevision.com
Salinity intrusion year round even during higher winter Net Delta Outflows
Average 1ft sea level riseX2 is up to 4.5km eastward with climate change and sea level rise
Wang et al., 2018 http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-004.pdf
X2 with SLR
Mean Impact South of Delta Exports
• Decrease by 10% (521 TAF) in 2060
• Range -44% to +21%
• 16 of 20 scenarios project export reductions
• 9 of 20 scenarios project wetting trend, but only 4 of 20 project export increases
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Del
ta E
xpor
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AF)
Exceedance Probability (%)
Exceedance Probability of Delta Export under 20 CMIP5 Climate Change Scenarios
CMIP5
95% confidence level
95% confidence level
Base
Impacts assessed at mid-century (centered around 2060)
Mean Delta exports reduced by 10%(range -44% to +21%)
Wang et al., 2018) http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-004.pdf
South Delta Exports during Drought
Wang et al., 2018) http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-004.pdf
During future severe drought episodes for the driest climate projection, Delta exports would reduce to half of the exports in historical severe drought episodes.
1987-1992 Drought & Climate Change1987-1992 Drought
1929-1934 Drought & Climate Change1929-1934 Drought
Decision-Scaling ApproachDelta related metrics
Schwarz et al., 2018 http://www.climateassessment.ca.gov/techreports/docs/20180827-Water_CCCA4-EXT-2018-001.pdf
Performance MetricGlobal Climate Model-Based Probability that Mid-Century Performance will be Inferior to Current Performance
Net Delta OutflowWinter 63%Spring 65%Summer 21%Fall 40%
Annual Delta Exports 93%
Delta Flooding and Water Supply Risks from Sea Level Rise
Background Projections Research Take Home Messages
Delta Flooding and Water Supply Risks from Sea Level Rise
• Triple Threat sea level rise + storms + subsidence• Levees may not meet height standards by 2050-2080• Inflows into the Delta are affected by
precipitation/runoff shifts AND management decisions• Increased reservoir releases are a likely response to
maintain Delta water quality due to salinity intrusion, even at 1ft sea level rise
• Delta exports likely reduced, especially in droughts
