Shani Wallis, TunnelTalk

California's affair with long distance water tunnels is set to continue with another mega project in the planning. Involving a possible 78 miles or 125km of 33ft (10m) i.d. tunneling, the new supply line is needed to divert water about 43 miles around the ecologically sensitive Sacramento-San Joaquin Delta to the south of San Francisco Bay, protecting the environment and securing California's fresh water supply.

Fig1. Underground all the way is favored

The project would to convey water from the Sacramento River at a point near the town of Hood, south of Sacramento, to huge pumping stations south of the Delta near Byron where water is lifted into the canal system of the California State Water Project. The fully underground option started gaining traction last year as a more socially acceptable, less environmentally damaging alternative to building canals (Fig 1).

Where the canal options include up to 17 miles (27km) of tunneling work, the all underground option calls for two parallel tunnels of about 33ft (10m) in diameter for about 35 miles plus a single tunnel of equal diameter for a further 8 miles for a total of 78 miles or 125km of proposed (37ft (11.2m) o.d.) EPB or slurry TBM tunnelling with precast concrete segmental linings.

The planned project builds the last part of the California State Water Project. At present water flows in natural watercourses across the Delta from the Sacramento River to pumping stations near Byron where it is lifted into the state delivery canal systems for transfer of water from the abundant north to the needy south. The current system is unsatisfactory on several levels, according to project reports. The fresh water as it flows across the Delta is vulnerable to contamination by the salt water of the estuary and the whole area is vulnerable to flooding by rising sea levels. The high capacity pumps are also depleting natural fish stocks in the Delta. To protect endangered species, including wild salmon and the Delta smelt, pumping operations are turned off during the spawning season. This causes systems downstream to be underutilized.

Table 1. A comparison of project cost estimates at Nov 2009

Table 2. Comparison of project option maintenance costs

The Inland Feeder system in Southern California for example, would benefit by the new project. The delivery system to Diamond Valley Lake east of Los Angeles came on-line fully last year with completion of its vital Arrowhead tunnels, but the system runs at only marginal capacity when delivery of is restricted by pumping operations in the Delta area. "These limits cause severe water conservation measures on farmers and consumers in the Southern California area," said a spokesman of the MWD (Metropolitan Water District) of Southern California explained. "The plan is to channel a proportion of the fresh water that flows across the Delta into a protected channel of canals and/or tunnels" to safeguard the environment, protect the endangered species, restore environmentally damaged areas, and secure California's fresh water supplies by lifting limits on when and how much water can be delivered by the pumping station into the State Water Project system.

The multi-billion project is managed on behalf of the state Department of Water Resources by the Bay Delta Conservation Plan (BDCP), a coalition of environmental agencies and beneficiary water authorities, most notably San Joaquin Valley water companies and the Southern California MWD. The BDCP selected the all underground option for further study at its meeting last week on Thursday (11^th February) in Sacramento.

When compared to the two canal-tunnel alternatives, the all tunnel option is the most expensive at up to $11.6 billion. The lowest estimated alternative is the East canal-tunnel alignment at about $9 billion and the West alignment project has an estimate of about $10 billion. Beneficiary water agencies, including the MWD of Southern California, have agreed to pay for the project, passing the costs on to end users. The all tunnel option however suggests savings on annual maintenance costs.

Engineering firm URS is working on preliminary design studies for the project and steering it through the environmental impact process. A draft environmental study is not expected until the end of 2010. It would then progress towards approval by wildlife agencies to satisfy the Endangered Species Act. Preliminary reports are based on a eight-year construction period starting in about 2013 and finishing in 2022. Many TBMs working simultaneously would be required to meet that construction schedule. EPB or slurry TBMs would be needed to work through the deep, waterbearing sedimentary deposits of the Delta geology. The twin 33ft (10m) i.d. tunnels and their necessary six pumping stations would transfer water at up to 15,000ft3/sec. The project has been under discussion for some time and has attracted a high political profile. Millions of Californians and vast tracts of farmland already depend on the Delta for water supplies and diverting more to feed the high demand areas of the south is seen by many as non-viable and damaging to their economy in the long term. Most Delta residents also oppose the project with many lawsuits already mounted against property owners who refuse access for surveys and site investigation studies for the canal options. The full tunnel option is seen as mitigating much of this opposition by minimizing environmental damage and limiting substantially land appropriation needs. The administration of state Governor Schwarzenegger has also weighed in, supporting the plan and stating it has the legal authority to go ahead with project construction.

Comparing the options West canal East canal All tunnel Construction cost(billions) $9.1-10.8 $8.6-9.4 $10.2-11.6 Canal miles 38 40 - Tunnel miles 17 2 78 Bridges 20 18 - Utility conflicts 300 150 70

A new governor however will be in charge from November this year when Governor Schwarzenegger's second term comes to an end. The deputy director of the DWR is reported as saying that the Department is pleased that the tunnel option is being studied and environmental groups involved are reported as agreeing to further study of the tunnel option but have yet to support its construction.

References

2009 in retrospect - Arrowhead comes on-line - TunnelTalk, December 2009
Final breakthrough for Arrowhead - TunnelTalk, August 2008
Clawing success from the extreme at Arrowhead - TunnelTalk, December 2007

The Bay Delta Conservation Plan

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