Delta tunnel: US Army Corps application has new Eastern alignment

On Wednesday, June 17, 2020, the Department of Water Resources (DWR) submitted an application for a Section 404 Clean Water Act permit for the Delta tunnel to the US Army Corps of Engineers.  With the application, the Department of Water Resources submitted a map of the proposed project, which included the Eastern alignment for the main tunnel, and Intakes 3 and 5 (p. 37, shown below.)

USACE application map

In an accompanying announcement, the Department of Water Resources stated that the submission of the project map to the Army Corps of Engineers with the Section 404 application “is preliminary and should not be construed as a decision by DWR regarding its preferred project.” However, the evaluation of the project does represent a significant commitment of engineering resources, both by the US Army Corps and by the Department of Water Resources.

The selection of the Eastern alignment is a major change from the Central Delta alignment that has been studied for over a decade.  The change is likely driven by major logistical issues with construction of a tunnel and shafts through the Central Delta.

In December of 2019, an Independent Technical Review panel of engineers from five international tunneling companies found that the Central Corridor was logistically impractical.  The ITR panel’s report stated:

The shaft locations are located a significant distance from Interstate 5, accessible by only farm roads with hindrances such as narrow weight-restricted bridges and single lanes. This makes supporting large operations, which requires a constant transfer of materials and people in and out, impractical and expensive as well as difficult to price.

The panel further stated:

While it was recognized that extensive roadway, levee, and likely barge improvements could be constructed as part of the project for the Central Corridor… [t]he cost of improvements to provide reliable and safe access and egress at each site would exceed the cost of additional length of tunnel required for the East alignment.

One example of access issues was the construction of a tunnel shaft on Bouldin Island.  The tunnel shaft was originally planned to be 30 feet above sea level to ensure protection from 200 year floods plus sea level rise.  Since Bouldin Island is 18 feet below sea level, this would require construction of an enormous 48 foot high mound for the tunnel shaft pad.

Bouldin Island tunnel shaft
Simulated view of Bouldin Island Tunnel Shaft mound (closeup)    Source: DWR, 2018 WaterFix EIR

The Delta Conveyance Design and Construction Authority’s traffic analysis found that hauling the fill in to build the mound would require widening Highway 12 to four lanes, westbound from I-5.  A study for CALTRANS in 2006 found that widening Highway 12 to three lanes would cost over $77 million, which is over $98 million in 2020 dollars.  This was just one of extensive roadway improvements and barge landings that would be needed for the Central Delta route.

The change to the Eastern alignment has the added benefit of reducing impacts of the tunnel construction on boating and recreation in the Delta, as well as on historic Chinese and Japanese American districts in Locke and Walnut Grove.  The Eastern alignment also avoids constructing a tunnel shaft in the middle of some of the densest sandhill crane habitat on the west coast, which is shared with huge numbers of migratory waterfowl, with winter counts on Staten Island alone in the tens of thousands.

Sandhill Cranes small
Sandhill Cranes, Sacramento Delta      Source: Shutterstock   

Shifting the tunnel route to the east also significantly reduces the risks of tunnel boring. The Central Delta route tunneled under some of the most subsided islands in the Delta.  Delta Reclamation Districts and their engineers were very concerned about the risks of flooding if the tunneling compromised a levee.  They were also very concerned about the tunnel construction traffic compromising their ability to patrol levees during times of high water.

For these reasons, the selection of the Eastern alignment was greeted with celebration by the Discovery Bay based group, Save the California Delta Alliance.  However, the group did state that impacts of the Eastern alignment still need to be assessed.

The Delta Conveyance Design and Construction Authority’s traffic analysis did show unacceptable Levels of Service for traffic on Byron Highway during commute times for both the Eastern and Central tunnel alignments. The DCA is proposing to construct a new railroad spur adjacent to the Byron Highway to haul construction materials.  This would partially alleviate impacts on Byron Highway. Traffic on Highway 4 is projected to have small increases but to stay within acceptable levels of service.

Byron Highway Traffic
Eastern Alignment Traffic Analysis         Source:  DCA 5-27 presentation

The project is also expected to increase traffic on I-5 in Stockton by 1-4% during peak commute times.  The DCA’s traffic analysis projects that the Level of Service during peak commute times on I-5 will be unacceptable, but the congestion will be primarily due to pre-existing traffic.

I-5 traffic DCA
I-5 Traffic Analysis     Source:  DCA 5-27 presentation

3 thoughts on “Delta tunnel: US Army Corps application has new Eastern alignment

    1. Unfortunately, it isn’t a “done deal” yet. They have not “chosen” an alignment. But … that being said, we were all encouraged when DWR used the Eastern Corridor for their 404 permit instead of the Central … since in the past the Central was their primary focus. In no small part because Metropolitan Water District purchased several islands on the Central Corridor route years ago in anticipation. So we hope this is positive news for the construction phase not to destroy waterways and waterfowl … but I’m sure there are issues with the Eastern and with any tunnel, less water flows through the Delta.

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