Sea level rise and Delta subsidence—the demise of subsided Delta islands

Jay R. Lund, the Ray B. Krone Professor of Environmental Engineering, University of California – Davis

Aerial view of Jones Tract levee break 2004: DWR photo

Periodically, scientists point to the weaknesses of levees in the Sacramento-San Joaquin Delta.  The press and policy makers respond with astonishment, followed by local assertions of levee sustainability and pleas for greater subsidies.  This cycle has recurred several times in recent decades.

California relies on these Delta levees for a wide range of water supply, water quality, land use, and agricultural purposes.  Nevertheless, the state needs a realistic Delta levee policy, one that will not view every subsided Delta island as hallowed ground.

Here is a time line of published technical and scientific work and events indicating that many Delta levees are at substantial risk, involving independent researchers using diverse methods over several decades:

1931 – California decides that regulating flows into the Delta is more economical than building a barrier across the Delta near Benicia, in part because raising Delta water elevations would likely flood many Delta islands (Matthew 1930).

Frank's Tract

1937, 1938 – Frank’s Tract, a Delta island, floods and is eventually abandoned by its owners. Now a major fishing and state recreation area.

1953 – Biemond Plan, commissioned by the Department of Water Resources (DWR), proposed reducing the current 1,100 miles of Delta levees to 450 miles, with the newer levees having reconstructed foundations (Jackson and Paterson 1977)

1957 – Thompson (1957) in his Stanford dissertation on human settlement of the Delta notes many long-term challenges for the Delta’s levees, including: the heightening of flood flows due to the reclamation of marsh lands over which flood waters formerly spread; and higher channel beds from mining sediment in the late 1800s and early 1900s. (Many Delta channel bottoms are higher than nearby island interiors.)

1978, 1983 –University of California Berkeley engineers (Houston and Duncan 1978; Duncan and Houston 1983) find high failure probabilities for many Delta levees (US Army Corps of Engineers-funded).

1983 – Mildred Island levee fails, with the island being flooded and abandoned by its owners, and becomes a home for many fish species in the South Delta.

1990 – Logan (1989, 1990) finds the cost of improving many Delta levees is not economically justified.

Liberty Island--flooded in 1998 and abandoned by its owners.

1998 – Liberty Island levee fails, with the island being flooded and abandoned by its owners.  This is now a home for delta smelt.

2000 – CALFED and DWR commission a study of seismic risk (Torres et al., 2000).  Study involves local engineers and demonstrates high probability of levee failure due to earthquakes.

2003 – USGS (2003) estimates high probabilities of a major earthquake in the Delta and Bay Area.

Jones Tract flood in June 2004: DWR photo

2004 – Jones Tract fails on a sunny June day with a higher than normal tide.  Island is repaired at great expense to the state, due to major transportation infrastructure on the island.

2005 – Mount and Twiss (2005) find that many Delta levees are inherently weak and many islands are likely to become permanently flooded without unreasonably expensive levee subsidies from the state and federal governments.

2007, 2009 – Delta Risk Management Strategy (DRMS).  Major study commissioned by the Department of Water Resources (DWR 2009; URS Corporation and Jack R. Benjamin and Associates, Inc. 2007) finds that many islands are likely to fail due to earthquake and floods, would be very expensive to upgrade or repair, and that failure during an earthquake could have major effects of California’s Delta water supplies.

2009 – Subsided Bradford Island is almost sunk when hit by a straying freighter from the Port of Stockton.

Levee decision analysis based on property value and assets

2008, 2010 – Suddeth et al. (2008, 2010) and Lund et al (2008, 2010) find that about half of the Delta’s 36 subsided agricultural islands do not have sufficient economic value to justify major long-term upgrades for sea level rise or repair when they fail.

2011 – R. Bea of Berkeley declares the Delta levee network as “the worst damn mess I’ve ever seen, and I’ve seen some pretty bad ones” (Contra Costa Times);  USGS presentations to Delta Stewardship Council concludes that earlier studies have significantly underestimated seismic risk in the Delta.

Flooded trailer park in Mossdale, 1997.

For over a century, Delta reclamation districts and their engineers have worked valiantly to maintain Delta levees.  In this time, several islands have been abandoned, but many more have been repaired.  Nevertheless, continued subsidence, sea level rise, climate change, earthquake, and increasing repair and maintenance costs mean that many islands in the central and western Delta are unlikely to be repaired if flooded.

While local levee engineers and reclamation districts have done a remarkable job for local land owners in prolonging the lives of many Delta levees, numerous island failures seem inevitable, especially in the central and western Delta.  State policy should reflect this inevitability, and opportunity.  Whether these islands fail with a bang or a whimper seems less important than the fact that more islands in the central and western Delta will fail.

While the flooding of islands will harm local agriculture and some pose risks to water supplies, the large expanses of open water created will provide more habitat for fish and increased opportunities for water-based recreation including fishing and boating.  It is even possible, if highly uncertain, that the new open-water habitat will favor some Delta species now in serious decline such as delta smelt (Moyle 2008).

References and Further Reading

Duncan, J.M. and W.M. Houston (1983), “Estimating Failure Probabilities for California Levees,” Journal of Geotechnical Engineering (ASCE), Vol. 109, No. 2, February, pp. 260-268.

DWR (2009), Delta Risk Management Strategy, California Department of Water Resources, Sacramento, CA.

Finch, M. (1985), “Earthquake Damage in the Sacramento-San Joaquin Delta, Sacramento and San Joaquin Counties,” California Geology.

Houston, W. M. and J.M. Duncan (1978), “Probability of Failure of Levees in the Sacramento-San Joaquin Delta, California,” Final Report, Corps of Engineers, Sacramento District, Engineering Division, Foundation and Materials Branch, Sacramento, Calif.

Jackson, W. T. and A. M. Paterson, The Sacramento–San Joaquin Delta and the Evolution and Implementation of Water Policy:  An Historical Perspective, California Water Resources Center, Contribution No. 163, University of California, Davis, June, 1977.

Logan, S.H. (1989), An economic analysis of flood control policy in the Sacramento-San Joaquin Delta, Contribution 199, California Water Resources Center, Davis, CA, June.

Logan, S.H. (1990a), “Global Warming and the Sacramento-San Joaquin Delta,” California Agriculture, Vol. 44, No. 3, pp. 16-18.

Logan, S.H. (1990b), “Simulating Costs of Flooding under Alternative Policies for the Sacramento-San Joaquin River Delta,” Water Resources Research, Vol. 26, No. 5, May, pp. 799-809.

Lund, J., E. Hanak, W. Fleenor, W. Bennett, R. Howitt, J. Mount and P. Moyle, Comparing Futures for the Sacramento-San Joaquin Delta, University of California Press, Berkeley, CA, February 2010.

Matthew, R. (1930), Economic Aspects of a Salt Water Barrier Below the Confluence of Sacramento and San Joaquin Rivers, Bulletin 28, Division of Water Resources, California Department of Public Works, Sacramento, California.

Mount, J.F. and R. Twiss (2005), “Subsidence, sea level rise, seismicity in the Sacramento-San Joaquin Delta,”  San Francisco Estuary and Watershed Science, v. 3, article 5, 2005.

Moyle, P. (2008), “The Future of Fish in Response to Large-Scale Change in the San Francisco Estuary, California,” in Mitigating Impacts of Natural Hazards on Fishery Ecosystems. K.D. McLaughlin, editor. American Fishery Society, Symposium 64, Bethesda, Maryland.

Suddeth, R., J. Mount, and J. Lund (2008), “Levee Decisions and Sustainability for the Sacramento-San Joaquin Delta,” Appendix B to Comparing Futures for the Sacramento-San Joaquin Delta, Public Policy Institute of California, San Francisco, CA, August.

Suddeth, R., J. Mount, and J. Lund (2010), “Levee decisions and sustainability for the Sacramento San Joaquin Delta“, San Francisco Estuary and Watershed Science, Volume 8, No. 2, 23pp, August.

Thompson, J. (1957), Settlement Geography of the Sacramento-San Joaquin Delta, California, dissertation, Stanford University.

Torres R.A., et al. (2000), Seismic vulnerability of the Sacramento-San Joaquin Delta levees. Report of levees and channels technical team, seismic vulnerability sub-team to CALFED Bay-Delta Program. 30 p.

URS Corporation and Jack R. Benjamin and Associates, Inc., 2007, DRAFT Delta Risk Management Strategy (DRMS) Phase 1 Risk Analysis Report: prepared for the California Department of Water Resources (DWR).

USGS (2003), Earthquake Probabilities in the San Francisco Bay Region: 2002–2031, U.S. Geological Survey, Open-File Report 03-214.

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