Oroville Dam annual inspections found water “seepage” on the face of the dam and have been warning about potential structural steel failures since 2014.
Breitbart News has obtained through Agenda 21 Radio the Oroville Dam’s annual ‘Inspection of Dam and Reservoir in Certified Status’ by State of California Division of Safety of Dam for the years 2014, 2015 and 2016.
According to the September 18, 2014 inspection report, Oroville Dam had water seepage issues on the face of America’s tallest dam that that were described as a “long established wet area at the mid-slope of the left end of the dam.” Although the area was dry in 2014 due to drought, inspectors only approved “interim use” of the dam based on the implementation of a long term monitoring of the “phreatic surface within the dam.”
Inspectors also commented that the cracking around the cement seams at the gates on top of Oroville Dam’s main spillway were a serious concern because “tendon anchors are about 50-year old and could experience problems in the future based on the history of tendon breakage at dams of similar age and construction.”
According to the Civil Engineering Dictionary, such dam seepage means that the phreatic line of the top of the ground water table is evidence of water leaking through a dam’s internal barrier wall that should be impervious to water.
Although the Division of Safety of Dam did not detail in 2014 why the face of Oroville Dam had a long term history of suffering from seepage, the International Water Power and Dam Construction Magazine in a 2008 article titled, ‘Dangers at Embankment Dam Boundaries and Embedments,’ pointed to Oroville Dam as the text book example of issues associated with stress cracking within an earthen dam’s internal water barrier.
According to the article, during 1960s construction, a 900 foot long and 120 foot high concrete block wall was built on the dam’s rock foundation as a water barrier. But the “thrust” pressure as a sloping dirt wall was piled up to a height of 770 feet, caused rotation in the concrete barrier wall. As a result, longitudinal cracking developed in the top 50 feet of the barrier block wall, which was only made of unreinforced concrete.
With “block and longitudinal cracking with openings of several inches,” the barrier wall cracks and joints were supposedly sealed by “injection of cement grout.” Instrumentation at the time supposedly showed that the remedy was “successful.”
The State of California Division of Safety of Dam 2015 inspection again only approved the Oroville Dam for “interim use” due to seepage. But the report also highlighted numerous cracks on the top of the Oroville Dam’s spillway and cracking in the pillars and construction joints of the dam’s water release gates. The report for the first time suggests that the high-tensile structural steel anchor tendons “may be approaching the end of their useful life.”
The Division of Safety of Dam’s 2016 inspection gave Oroville Dam another “interim use” approval, based on the same concerns as the 2015 report. But the Board of Safety of Dam specifically “expressed concern” about the risk of tendon anchors breaking due to age and stated that they “will make strong recommendations about the need to carefully monitor and test the tendons using the latest tools.”
When Breitbart News contacted the California Division of Safety of Dam to request interviews with the dam inspectors and copies of any follow-up reports regarding the 2014, 2015 and 2016 inspections of Oroville Dam, we were informed that all questions would require filling in writing a Freedom of Information Act request.