Tallest US dam has a damaged spillway which causes the evacuation of about 188000 people

About 188,000 residents near Oroville, Calif., were ordered to evacuate Sunday after a hole in an emergency spillway in the Oroville Dam threatened to flood the surrounding area. Thousands clogged highways leading out of the area headed south, north and west, and arteries major and minor remained jammed as midnight approached on the West Coast — though by early Monday, Lake Oroville’s water level had dropped to a point at which water was no longer spilling over, and the crisis appeared to be stabilizing.

The lake level reached its peak of 902.59 feet at about 3 a.m. Sunday and dropped to 898 feet by 4 a.m. Monday, according to the Sacramento Bee. Water flows over the emergency spillway at 901 feet.

“The drop in the lake level was early evidence that the Department of Water Resources’ desperate attempt to prevent a catastrophic failure of the dam’s emergency spillway appeared to be paying dividends,” the Bee reported Monday.

Repair crews are hoping boulders will help be the stopgap against erosion at the Oroville Dam emergency spillway. The California Department of Water Resources says the plan is to drop large rocks and boulders, called rip-rap, into the erosion causing concern at the emergency spillway. DWR’s hope is that they’ll be able to drop enough rock to protect the impacted area from further erosion. Helicopters will be used to drop in the boulders.

A spillway failure could cause 35 foot wall of water to hit some of the town below the dam.

Rain is forecasted for this Thursday and Friday.

The 770-foot-tall Oroville Dam is the nation’s tallest, about 44 feet higher than the Hoover Dam on the Colorado River. The lake is the linchpin of California’s government-run water delivery system, sending water from the Sierra Nevada for agriculture in the Central Valley and for residents and businesses in Southern California.

Officials doubled the flow of water out of the nearly mile-long primary spillway to 100,000 cubic feet per second. The normal flow is about half as much, but increased flows are common at this time of year, during peak rain season, officials said.

After a record-setting drought, California has been battered by potentially record-setting rain, with the Northern California region getting 228 percent more than its normal rainfall for this time of year. The average annual rainfall of about 50 inches had already been overtaken with 68 inches in 2017 alone.

There was never any danger of the dam collapsing. The problem was with the spillways, which are safety valves designed to release water in a controlled fashion, preventing water from topping over the wall of the colossal dam that retains Lake Oroville.

Lagging infrastructure maintenance

For decades, there has been lagging maintenance of American infrastructure

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