Dive Brief:
- Officials broke ground on the $200 million second phase of upgrades for California's Isabella Dam, according to KBAK & KBFX Eyewitness News.
- In phase two, workers will raise the dam 16 feet and mend existing leaks, as well as increase the ability of the auxiliary dam to withstand a seismic event. The dam straddles an active fault, so crews will also add filters, drains and a new 300-foot-wide spillway, according to KGET.
- An earlier investigation by Eyewitness News into the dam's safety led the Army Corps of Engineers to develop a strategy to strengthen the structure and protect the approximately more than 300,000 people living below it. In 2006, an internal report obtained by Eyewitness News noted the Isabella Dam had an "unacceptably high probability of failure combined with a very high consequence of failure."
Dive Insight:
Although the Army Corps has been working to improve Isabella Dam's safety for more than a decade, the spotlight has been on California dams since the Oroville Dam spillway failure last February. The event led to the evacuation of 188,000 Sacramento-area residents and kicked off inspections of other dams in the state.
Since then, a California Department of Water Resources (DWR) memo has surfaced indicating potential structural issues with seven other dams. The memo, which the DWR sent to the California Division of Safety of Dams (DSD) and Federal Energy Regulatory Commission (FERC), reflected engineers' concerns that the dams in question were similar in age, construction and design to the one in Oroville and that the potential existed for "geologic, structural or performance issues that could jeopardize their ability to safely pass a flood event.” The seven dams in the memo are also classified as hazardous, meaning a failure would likely cost lives.
The American Society of Civil Engineers (ASCE) found that more than 90,000 U.S. dams are, on average, 56 years old and that 70% of dams will be more than 50 years old by 2025. In addition, more than $64 billion, according to the Association of State Dam Safety Officials, is required to repair all federal and non-federal dams. The U.S. Army Corps of Engineers has said it will need more than $25 billion to repair the dams under its control.
