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#Post#: 13916--------------------------------------------------
Oroville Dam
By: Kerry Date: February 13, 2017, 11:16 pm
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First I heard that there was a problem with the Oroville Dam but
that it posed no danger to anyone. That's what the local paper
HTML http://www.orovillemr.com/general-news/20170207/oroville-dam-spillway-damaged-dwr-says-no-public-danger?source=most_viewed<br
/>reported too:
Oroville >> The Lake Oroville spillway was damaged by increased
water releases Tuesday, prompting the Department of Water
Resources to shut off the flow temporarily.
The public is not in danger, DWR said.
DWR had planned to increase releases via the spillway to 65,000
cubic-feet per second Tuesday morning, but halted around noon
due to erosion of the spillway, the cause of which is being
investigated, according to a press release issued by the
department Tuesday afternoon.
So the public was not in danger, eh? So they said. Not too
much later, that changed. Again from the local paper
HTML http://www.orovillemr.com/general-news/20170212/180000-evacuate-because-of-emergency-spillway-danger:
Oroville >> An estimated 180,000 people were ordered to evacuate
along the Feather River on Sunday afternoon after erosion raised
fears the emergency spillway at Oroville Dam could fail.
The state Department of Water Resources said about 3 p.m. Sunday
a hole developed in the emergency spillway as water cascaded
down the dirt ravine. The erosion appeared to be spreading
upward toward the structure.
If the emergency spillway structure — a concrete lip on the
north side of the dam — were undercut by the enlarging chasm, it
could fail, and the water behind that barrier would come down
the hill uncontrollably into the diversion pool and down the
Feather River, setting the stage for the possibility of massive
flooding into Oroville and communities farther south, officials
said.
Another story
HTML http://www.orovillemr.com/general-news/20170210/recent-oro-dam-spillway-inspections-found-nothing-suspect?source=most_viewed<br
/>gave more details about past inspections:
Oroville >> The most recent inspection of the Oroville Dam
spillway was conducted about six months ago, according to the
Department of Water Resources, and nothing at the spillway
seemed amiss, according to the reports.
This newspaper requested the most recent inspection reports of
the spillway and received documents from August 2016, July and
February 2015, and a report from June and August in 2014.
At Friday’s afternoon press conference, DWR civil engineer Kevin
Dossey, said spillway voids are common and confirmed Oroville’s
spillway surface was repaired in 2013 near where Tuesday’s
failure occurred. He said the spillway has never undergone major
repair.
The inspections were conducted by the Division of Safety of
Dams. The reports list no aspect of the spillway as
unsatisfactory or out of the ordinary.
Both the most recent report and the report from February 2015
note a “long-standing diagonal crack” on the left pier for one
of the gates, but they say the crack had not extended to the
point where it required an investigation.
The emergency spillway weir was described as stable appearing
and unchanged from previous inspections.
During the inspection in 2015, in July, the structure was again
found to be stable and satisfactory. Although, inspectors looked
at the discharge channel “from some distance” rather than
walking it, the report says. Inspectors determined there were no
visible issues with the concrete.
But then we have this from the Mercury News
HTML http://www.mercurynews.com/2017/02/12/oroville-dam-feds-and-state-officials-ignored-warnings-12-years-ago/:
More than a decade ago, federal and state officials and some of
California’s largest water agencies rejected concerns that the
massive earthen spillway at Oroville Dam — at risk of collapse
Sunday night and prompting the evacuation of 185,000 people —
could erode during heavy winter rains and cause a catastrophe.
Three environmental groups — the Friends of the River, the
Sierra Club and the South Yuba Citizens League — filed a motion
with the federal government on Oct. 17, 2005, as part of
Oroville Dam’s relicensing process, urging federal officials to
require that the dam’s emergency spillway be armored with
concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy
Regulatory Commission. They said that the dam, built and owned
by the state of California, and finished in 1968, did not meet
modern safety standards because in the event of extreme rain and
flooding, fast-rising water would overwhelm the main concrete
spillway, then flow down the emergency spillway, and that could
cause heavy erosion that would create flooding for communities
downstream, but also could cause a failure, known as “loss of
crest control.”
“A loss of crest control could not only cause additional damage
to project lands and facilities but also cause damages and
threaten lives in the protected floodplain downstream,” the
groups wrote.
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