Spillway actually, not the dam. From The Landslide Blog:
Oroville Dam: extraordinary erosion, and a crisis, on the spillway
The Oroville Dam in California is the tallest dam in the USA. with a height of 230 m, this is an earthfill embankment dam built between 1961 and 1968 for the purposes of water supply, hydroelectric power generation and flood control. After years of drought, California is suffering a series of huge rainstorms – so-called atmospheric rivers – that have rapidly raised the water level in the dam. To allow flood control, the dam has been undergoing controlled discharges of water through the spillway.
On Tuesday, after such a release water, major damage was noted on the spillway, apparently caused by the failure of the concrete base and then erosion of the underlying substrate.
Over the next few days further discharges of water have been undertaken to test the spillway and to control the water level in the lake.
Unsurprisingly, the condition of the spillway has dramatically deteriorated:
The issue is that if they do not use the spillway, the water level could over-top the dam itself - something it was not designed for. San Francisco station KQED is following the story:
With Oroville Spillway Damage Spreading, Officials Prepare for Reservoir to Overflow
Update, 9:20 a.m. Friday: Two things have changed overnight at Oroville Dam and the giant reservoir behind it.
First: Inflow from the Feather River watershed into Lake Oroville, while still very high, has dropped from its peak levels Thursday.
Second: California Department of Water Resources managers followed through with a plan to ramp up releases down the dam’s wrecked spillway (for their rationale for doing that, see our earlier updates, below).
More at the site.
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