Pacheco expansion considered necessary for California, despite increased costs

The Pacheco dam expansion project in California, USA, is now likely to move ahead again, having been put on hold for three years, following the discovery of unstable rock at the site area. Contractors had discovered the need to excavate to a depth 10 m greater than expected to reach bedrock, and this, together with other factors, greatly increased the cost of the project.

It is estimated now that the project could take eight years, instead of five, to construct, and that the cost will increase by around US$ 1 billion to a total of US$ 2.5 billion. However, the severe water shortages in California in recent years have led members of the board of the Santa Clara Valley Water District, based in San José, to decide that the project, should go ahead, despite the higher cost.

The scheme has long been considered as a key part of water supply strategy for around 2 million people, in an area which has suffered from severe drought. Pacheco would be the largest dam and reservoir scheme to go ahead in the Bay area of California in at least 20 years.

The project will involve a 97 m-high dam on Pacheco Creek, which will replace a 33 m-high structure, currently impounding the Luis reservoir with a capacity of around 6.7 x 106m3. The enlarged reservoir formed by the higher dam will have an operational capacity of around 172.7 x 106m3.