Calaveras dam in San Francisco Bay Area is finally finished

Calaveras Dam, the larger dam built in Bay Area in 20 years, is finally completed.

The 220-foot tall dam is located in the area east of Interstate 680 on the Alameda-Santa Clara County. Being the tallest structure built in the Bay since 1998, it is a significant part of the Hetch Hetchy water system, which provides drinking water to 2.7 million people in Alameda, Santa Clara, San Mateo and San Francisco counties. It was constructed to replace an older dam (built in 1925) which was at the risk of collapse in a major earthquake on the Calaveras fault, according to inspections in 2001. If the old dam collapsed, huge floods would strike Fremont and neighboring communities, threatening hundreds of lives. The new structure will be able to withstand a M_w 7,25 earthquake, according to experts.

The construction of the dam was a difficult achievement. In the beginning, workers found 2 ancient landslides in the location and were forced to carve away tons of debris to anchor the dam in a more solid basis. Moreover, hillsides had to be supported more than expected and a flood in winter of 2016-2017 delayed the construction work by 3 months. The project was supposed to cost $409 million and be completed in 2015 according to a 2009 report. However, the actual cost reached $823 million, more than twice its initial expectation. Some parts including paving of nearby roads and installing electrical equipment and sensors in the dam will be finished in 2019 thus the final delay of the project will exceed 3 years.

Engineering experts state that the delays were unfortunate but also inevitable. "They didn't do anything wrong. It's like home remodeling. When you buy an old home, the walls all look sound. But when you go to replace the windows, you realize you have dry rot. But you still have to fix it," said Nicole Sandkulla, a civil engineer and CEO of the Bay Area Water Supply and Conservation Agency.

Inspectors ordered Calaveras reservoir to not exceed 40% of its capacity in order to minimize earthquake risks. The reservoir is now 25% full. Dan Wade, director of water capital projects for the San Francisco Public Utilities Commission said: "If we have a wet winter, it can fill in one year. But it could take four years. Or if we're in a drought, it could take longer."

Some people wondered why San Francisco didn't enlarge Calaveras reservoir, since the dam was replaced. Mr. Sandkulla stated that officials were worried about lawsuits and the difficulties of getting permission to accomplish a larger reservoir. In any case, Wade ensures that in a future case of exceeding needs, the dam has the potential to be raised 150 feet more, quadrupling reservoir's size.