California Aqueduct, Central Valley Project, Delta-Mendota Canal, Ecosystem, Fisheries, Intertie, Jones Pumping Plant, SLDMWA, State Water Project, Water Supply, Westlands

Record of Decision for the Delta-Mendota Canal / California Aqueduct Intertie

The California Aqueduct and Delta-Mendota Canal; courtesy of Bureau of Reclamation.

Last week, in the final days of 2009, it was announced that the long-planned Delta Mendota Canal/California Aqueduct Intertie project finally got its Record of Decision from the U.S. Department of the Interior. The federal government, in its Interim Action Plan for the Bay-Delta (PDF), released on December 22, 2009, also listed the Intertie as a priority project to expedite, aiming to have construction start by June 2010 and completed by October 2011.

The $34 million proposed Intertie, which will be located in Alameda County generally west of Tracy, would connect the Delta-Mendota Canal, a federal facility, to the California Aqueduct, a state facility. The proposed project takes the form of a pipeline connection from milepost 7.2 of the Delta-Mendota to milepost 9 of the Aqueduct, where the state and federal projects are only about 500 feet apart. The Intertie would be owned by the U.S. Bureau of Reclamation, but operated by the San Luis and Delta-Mendota Water Authority (SLDMWA), which consists of numerous members, mostly federal contractors, including Westlands Water District. The basic goal is to increase the operational flexibility of the state and federal projects. The Intertie project includes a 467 cfs pumping plant on the Delta-Mendota to pump water underground a vertical distance of 50 feet up to the Aqueduct, and it would also permit a 900 cfs reverse flow by gravity from the Aqueduct to the Delta-Mendota.

While the Intertie is largely advertised as a project that would be useful during both emergency outages and rounds of maintenance, it would also serve as a regular supplement to current levels of pumping. Both the federal and state projects have committed themselves to deliver more water to contractors than they can realistically provide most of the time. The situation is amplified by an evolving understanding of how to regulate the flows that are needed in the Delta to protect fisheries and maintain water quality, as captured in subsequent decisions from the State Board. And so, while the Intertie would allow for operational flexibility in an emergency, it also facilitates making the most of the capacity at Jones on a regular basis — increasing at least somewhat the volume of Delta water pumped, and aiding Reclamation in its struggle to more reliably deliver supplies to its south-of-Delta contractors.

The issue is that there is some extra federal project capacity that currently cannot be used. The Jones Pumping Plant is authorized to pump at 4,600 cfs capacity, which is the full design capacity of the Delta-Mendota Canal. However, the O’Neill Pumping Plant, which pumps water into the O’Neill Forebay, has a capacity of 4,200 cfs. Because of this bottleneck, during fall and winter, Jones pumps below its design capacity. That 400 cfs of extra capacity could be captured, however, if the Intertie pumps the remainder to the California Aqueduct, and then to San Luis Reservoir.

The short table below briefly summarizes average pumping activity at Jones and Delta-Mendota deliveries from 2005 to 2007, as reported by the Bureau of Reclamation:

Year Jones Pumping Plant (cfs) Delta-Mendota Canal (af)
2005 3,736 2,705,829
2006 3,587 2,598,435
2007 3,571 2,586,383

The model considers the annual demand for CVP water flowing through the Delta-Mendota to be 3,332 TAF. But the demand is largely seasonal, peaking between May and August. Especially during those months, demand outpaces capacity, requiring that deliveries be supplemented with 782 TAF of water stored in San Luis. Meanwhile, pumping can increase between October and March, both to deliver supplies and to fill San Luis. In the unrealistic scenario of Jones consistently pumping at maximum capacity with the Intertie, the difference from the status quo is the pumping of an additional 136 TAF per year. Factoring in seasonal restrictions on pumping, there would be an average annual increase of 35 TAF.

The Bureau considered two other substantive alternatives in its NEPA analysis. One alternative is very similar to the proposed project, but is located about four miles to the south — where the two facilities are further apart, but avoids 500-kV transmission lines of the California-Oregon Transmission Project. Another alternative contemplates a temporary intertie about half-mile south of the proposed project, and this alternative takes advantage of the State Water Project’s unused conveyance capacity at the Banks Pumping Plant to convey the additional CVP water to San Luis Reservoir, resulting in an average annual increase in 27 TAF (compared to 35 TAF for the proposed project).

Intertie project area. Courtesy of U.S. Bureau of Reclamation.

The idea to connect the state and federal projects south of the Delta pumping plants has been lingering for awhile. As early as 1988, the Bureau examined such a project jointly with Westlands to augment supplies conveyed to Westlands or San Luis Reservoir. In 2000, the intertie was a component of the CALFED program Record of Decision. Then, in 2005, Reclamation and the SLDMWA again studied the project. From the environmental assessment Reclamation concluded that the project would not result in significant environmental impact, and the SLDMWA issued a Mitigated Negative Declaration. A lawsuit subsequently challenged the FONSI, and Reclamation then prepared a full EIS for the Intertie, ultimately concluding that the most of the changed conditions were not significant adverse effects, and those that were could be mitigated.

One potential source of concern in the future is the way that the CALSIM II model used in the Bureau’s simulation has shaped our general understanding of the Intertie. The simulation yields outputs on a monthly scale, taking into account many globally relevant operational requirements. These include: water allocated under the CVPIA, Decision 1641 salinity standards, the Vernalis flow requirements, and other operational requirements from throughout the large CVP/SWP geographic area. The model, however, is unable to report on a short-term basis (day-to-day, or week-to-week) the effects of operating the Intertie, and this more fine-tuned analysis would give a better sense of the project’s true impacts on fisheries (which the Bureau has so far claimed will not be adversely affected by the Intertie, and in some cases, may even benefit from it). In addition, CALSIM II employs past conditions from the years 1922-2003 to produce future outputs. Although this is a long span of time that has witnessed a wide variety of hydrologic conditions, these data are not necessarily reliable indicators of the future changes in hydrologic conditions that have been predicted as the result of climate change.



One thought on “Record of Decision for the Delta-Mendota Canal / California Aqueduct Intertie

  1. I really appreciate the time you took to analyze the Intertie here–even though I may not understand the entire picture ;>

    Posted by Dan | 13 April 2010, 11:31 am

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