Scientific integrity in DWR’s engineering: sea level rise

The WaterFix tunnel design assumes 18 inches of increase in water levels in the Delta by Late Long Term (2065) due to sea level rise. All structures, including tunnel intakes, tunnel shafts, the Intermediate Forebay, and the new parts of Clifton Court Forebay are being designed to withstand a maximum increase in water level of 18 inches. But hydrodynamic simulations by the U.S. Army Corps of Engineers show much greater changes in water levels in the Delta with 1.68 meters (5.5 feet) of sea level rise, which could be reached by the end of this century.

USACE water level change 168m

Simulated operations of the three intake, twin tunnels project have also only considered salinity intrusion with a maximum of 18 inches of sea level rise. Simulations by the U.S. Army Corps of Engineers show severe salinity intrusion with 1.68 meters (5.5 feet) of sea level rise.  These simulations do not include levee failure.

Max salinity intrusion with 1.68 m sea level rise                U.S. Army Corps of Engineers

The Department of Water Resources’ assumptions about sea level rise date back to 2009. By 2013, when the first BDCP Draft Environmental Impact Report / Environmental Impact Statement (EIR/EIS) came out, it was clear that the sea level rise estimates were obsolete. But the Department of Water Resources was reluctant to analyze higher values of sea level rise, stating in the Draft EIR/EIS that “the modeling analysis for BDCP had been designed and performed.” (Chapter 29, p. 13.)  Doing a new analysis would also have been expensive.

In a 2014 review, the Delta Independent Science Board was harshly critical:

The potential effects of climate change and sea-level rise are underestimated. . . . The potential direct effects of climate change and sea-level rise on the effectiveness of actions, including operations involving new water conveyance facilities, are not adequately considered. . . . We believe this is dangerously unrealistic.

DWR responded to the Delta ISB’s review, stating that “the scope of an EIR/EIS is to consider the effects of the project on the environment, and not the environment on the project.”

What could go wrong?

Jones Tract Flood 2004
Jones Tract Flood, 2004.      Source:  CA Water Blog

The graph below shows 2017 projections of sea level rise by the U.S. Army Corps of Engineers and NOAA Climate Change Center.  Under the highest rate of sea level rise, there is 18 inches of sea level rise by 2035 to 2040, when the Delta tunnel project would first start operating, and sea level rise would exceed 55 inches by 2065 to 2075 — within 30 to 40 years of initial operations.NOAA 2017 SLR 2100 SF

The Department of Water Resources quietly disclosed the risks of underestimating sea level rise in a new paragraph in an unrelated chapter of the December 2016 Final EIR/EIS:

• Underestimating sea level rise in the project design will result in harmful realized impacts such as flooding. Harmful impacts are more likely to occur if the project design is based upon a low projection of sea level rise and less likely if higher estimates of sea level rise are used. In situations with high consequences (high impacts and/or low adaptive capacity), using a low sea level rise value involves a higher degree of risk. (Examples of harmful impacts that might result from underestimating sea level rise include damage to infrastructure, contamination of water supplies due to saltwater intrusion, and inundation of marsh restoration projects located too low relative to the tides). (Chapter 9, section

The Ocean Protection Council’s Science Advisory Team Working Group released a new risk report for sea level rise in 2017. The highest sea level rise is projected for the highest greenhouse gas emissions. For the current climate change models, possible scenarios are called “Representative Concentration Pathways.” The highest Representative Concentration Pathway is RCP 8.5. For the RCP 8.5 scenario, there is a 28% chance that sea level rise at the Golden Gate will exceed 3 feet by 2100, and an 8% chance it will exceed 4 feet. Thus DWR’s use of sea level rise estimates of 18 inches for the WaterFix tunnels could result in a useful lifetime of less than 50 years for the project.

Sea level rise exceedance at the Golden Gate under highest GHG concentration pathway (RCP 8.5)

There is still significant uncertainty about catastrophic effects of climate change.    But these graphs show that using unrealistic assumptions for the $20 billion “WaterFix” project could result in severe and unanalyzed impacts on the project.

This post was revised on February 25, 2019 to include the new 2017 estimates of sea level rise from NOAA for the 4th National Climate Change Assessment and modeling of water level changes in the Delta by the US Army Corps of Engineers.


Griggs, G, Árvai, J, Cayan, D, DeConto, R, Fox, J, Fricker, HA, Kopp, RE, Tebaldi, C, Whiteman, EA (California Ocean Protection Council Science Advisory Team Working Group). Rising Seas in California: An Update on Sea-Level Rise Science. California Ocean Science Trust. 2017. Available at

National Research Council, Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future. Washington, DC: The National Academies Press. 2012. Available at

Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, J. Obeysekera, A. Sallenger. Global Sea Level Rise Scenarios for the US National Climate Assessment. 2012. Available at

Sweet, W.V., R.E. Kopp, C.P. Weaver, J. Obeysekera, R.M. Horton, E.R. Thieler and CZ. NOAA Technical Report NOS CO-OPS 083, Global and Regional Sea Level Rise Scenarios for the United States. 2017. Available at

U.S. Army Corps of Engineers, Sea Level Change Calculator. 2015. Available at

Delta Independent Science Board, Review of the Draft EIR/EIS for the Bay Delta Conservation Plan. 2014. Available at

Bay Delta Conservation Plan Public Draft EIR/EIS, Chapter 29 — Climate Change. 2013. Available at

WaterFix Final EIR/EIS, Volume IChapter 9 – Geology and Seismicity. 2016. Available at

California Water Research, Comments on Water Supply and Water Quality Modelling in the WaterFix RDEIR/SDEIS. 2015. Available at

Chris Clarke, New Sea Level Rise Study Calls Delta Tunnels Into Doubt, KCET. April 2016. Available at

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