Posted by: Deirdre Des Jardins | August 12, 2019

Delta tunnel: Sea level rise and elevation of the North Delta

On May 2, 2019, the Department of Water Resources published a fact sheet on “Modernizing Delta Conveyance Infrastructure Q&A.” The fact sheet states that the California Ocean Protection Council has recommended “that projects with a lifespan beyond 2050 be built to withstand 10 feet of sea level rise by 2100.” The Department of Water Resources is to be commended for recognizing the recommendations by the Ocean Protection Council.   Hopefully DWR will be using them in assessing climate change and “efforts to modernize Delta conveyance.” per Governor Newsom’s April 29, 2019 Executive Order.

DWR’s Q& A fact sheet goes on to state:

“A reliable underground conveyance system is needed to move high flows from the northern portion of the Delta, which is over 15 feet above sea level, to the point that it can be exported to water systems in the Bay Area, Central Valley and Southern California.”

The statement that the northern portion of the Delta is over 15 feet above sea level is a bit misleading.  The US Geological Survey gives the elevation of Hood as 7 feet.   Maps from LIDAR data show that elevations at Hood over fifteen feet are on River Road, on top of the Sacramento River levee.  To the east of the levee, Hood is at 7-8 feet of elevation.

Hoodelev

The difference between 15 feet and 7-8 feet is critical for the Delta tunnel engineering design. Under NOAA’s 10 foot sea level rise scenario, sea levels could rise 7-8 feet by 2080.  If the Delta tunnel was completed by 2040, that would be within 40 years of initial operation.

If North Delta levees are not adequately maintained and upgraded, there could be flooding even without sea level rise. Courtland, just south of Hood, is at -1 ft to 3 ft of elevation, and is subsiding.  The map below shows elevations from LIDAR data collected by DWR and URS corporation.

North Delta elev closeup

legend

Channel profiles from the US Army Corps of Engineers show that the Sacramento River bottom in the vicinity of Hood is over 20 feet below sea level (Mean Lower Low Water in Suisun Bay.) If there was widespread levee failure in the Delta, it is unclear how far salinity would intrude up the Sacramento River at low flows.

SacRiverbottom

 

DWR’s assessment of “efforts to modernize Delta Conveyance” should include a discussion of whether further modeling is needed to evaluate salinity intrusion at the North Delta intake locations with 5-10 feet of sea level rise.

This post was updated on 8/14 to include an elevation map of the North Delta.


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