For three weeks in February , deluge of piddle rushed down the exigency spillway at Oroville dike , prompting fears that the total structure would collapse . novel images show what ’s pull up stakes of the 3,000 - invertebrate foot long concrete spillway — and the tremendous challenge that now face up reanimate crew .
airy photos of the Oroville dam show the bottom component part of the spillway all ripped to tatter , and a dramatic canyon wall with steep cliffs run along side of it . Bits of concrete , rock , clay , and timber lie at the bottom of the anatomical structure , clogging the Feather River .
Some 188,000 the great unwashed from Oroville had to be evacuated in mid - February after the spillway showed signs of unsuccessful person . hebdomad of heavy rain move functionary to turn overflow water from the massive reservoir , but once the rate of flow prove more than the chute could wield , concern emerged that the dike itself might give . Mercifully , the body structure held .
https://gizmodo.com/california-town-given-one-hour-to-evacuate-before-dam-s-1792281839
Earlier this workweek , California ’s Department of Water Resources turned off the catamenia of body of water , allowing for preliminary inspections of the damaged spill , and to allow worker to start on what looks like a monolithic cleanup . Once the debris is dispatch from the low channels , the DWR can resume flow through the dam itself and switch the hydroelectric plant life back on . The hydro flora has been out of natural process for weeks , removing819 megawatt of powerfrom the local grid .
As the new photos show , the damage is quite serious , and care remain about the integrity of deftness given that there are still five more hebdomad to go in California ’s rainy season — not to mention the million of gallons of water that will rush to the reservoir once the snowpack in the Sierra Nevada depart to melt .
The image above show just how difficult the fix are going to be . The eating away cause by the haste amnionic fluid create a sizable jam in the midsection of the spill . Writing in the American Geophysical Union’sLandslide Blog , geologist Dave Petley order the raw structure “ will need to be properly constitute onto competent rock ” as it appears that “ sections of the wasteweir that initially appear to be undamaged are in fact de-escalate . ”
Asreportedin the Sacramento Bee , official are devote some sentiment to make a Modern wasteweir in planning for the 2017 - 18 rainy season . In the lag , expert are n’t worried about the condition of the damage spillway , say it can still handle overflow waters should the need arise . It appear that the bedrock below the undamaged part of the spillway is much firm than the weather material on the upper percentage of the hillside . And when take with water , the golf hole created by the erosion should roleplay as a kind of jounce absorber . As one expert say the Sacramento Bee , “ It has the ability to absorb and dissipate energy . ”
The wasteweir was supposed to be able to address 250,000 three-dimensional foot of pee per second ( cfs ) , but its midriff collapsed on February 7th when a relatively tame 55,000 cfs pour out down it . Theories as to what move wrong are begin to issue . As the Sacramento Bee reports :
[ Engineering consultant Paul Tullis points ] to a phenomenon known as “ cavitation , ” in which the blast of tiny water bubbles gushing down the chute at 50 mph effectively seaman - forge hollow in weakened sections of concrete . Others , such as Robb Moss , a professor of geotechnical engineering at Cal Poly San Luis Obispo , muse that roots from tree growing along the sloping trough expanded weaknesses in the concrete .
[ David ] Rogers , the dam failure expert from Missouri , said the spillway may have had cracks that were n’t properly patched . He also theorized the loser may have been tied to California ’s five - year drouth : The aging spillway could have weakened as it undergo contraction due to the sudden heavy soaking follow years of dry weather .
The Federal Energy Regulatory Commission , which certify the dike , has ordered the land to open an probe .
[ Sacramento BeeviaLandslide Blog ]
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