Reconstruction & development |
Strengthening Anderson Dam
Chris Hakes, Deputy Operating Officer at Santa Clara Valley Water District in the US, gives an update on the Anderson Dam Seismic Retrofit Project
Below: Valley Water manages ten local reservoirs located across Santa Clara County that were constructed in the 1930s and 1950s. When full, Anderson Dam can hold more than the other nine reservoirs combined
SILICON VALLEY, LOCATED IN the heart of Santa Clara County, is the world’s tech capital and stands as one of the largest economies on the planet. Valley Water (Santa Clara Valley Water District) is the public agency responsible for providing safe, clean water, flood protection and stream stewardship to residents, businesses and farms in Santa Clara County. To help meet the region’s water supply needs, Valley
Water manages ten local reservoirs located across Santa Clara County. The reservoirs, constructed in the 1930s and 1950s, catch storm runoff that otherwise would flow into San Francisco Bay. It’s largest reservoir, Anderson, is in Morgan Hill and is vital to the region’s water supply. When full, the 71.6m high earthen dam can hold more than 112Mm3 of water, more than Valley Water’s other nine reservoirs combined.
Anderson Dam is located near the Coyote Creek Fault and Calaveras Fault and could be damaged by a large earthquake. In a worst-case scenario, a major earthquake could lead to the dam’s failure and an uncontrolled release of water. Because of the seismic concerns, Valley Water
operated Anderson Dam at 66% capacity from 2008 to 2017. The operating capacity was further reduced
22 | March 2022 |
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to 58% after 2017. Currently, Valley Water is retrofitting Anderson Reservoir to modern-day seismic safety standards, which will allow Valley Water to maintain the reservoir at maximum capacity.
Strengthening Anderson Dam Since Valley Water first began efforts to strengthen the
dam in 2012, the scope of the Anderson Dam Seismic Retrofit Project (ADSRP) has significantly expanded. Valley Water learned in 2016 that the dam itself needed a more extensive retrofit than initially thought. In 2017, following one of the wettest winters on record in the Sierra Nevada, the California Division of Safety and Dams changed the design criteria for spillways. Their decision required the existing spillway at Anderson to be completely replaced as opposed to repaired. On 20 February 2020, the Federal Energy Regulatory Commission (FERC), the agency that has oversight of Anderson Dam at the federal level, ordered Valley Water to lower water level in the reservoir to 3% capacity. FERC also ordered Valley Water to expeditiously build a new, larger outlet tunnel that could safely drain the reservoir in an emergency; and to continue working swiftly to complete design of the retrofit and obtain permits. In October 2020, Valley Water started lowering the
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