We go more rain than past few weeks than I can remember in 20, perhaps 30 years . I was complaining about my favorite fishing spots not melting out until July...!
But I’m sure glad I don’t live near Oroville Dam (north of Sacramento), because while the main dam is not at risk “a this time”, it looks like the never used emergency spillway is digging quite a gully, which could result in uncontrolled release of water if it back-cuts into the hillside and thence allows untold billions of gallons of water to rush downstream. The emergency spillway was put into use after the main spillway had a massive gap open up about 1/2 down from the top.
People downstream are under a mandatory evacuation order as of 5PM today:
"This is not a Drill. Repeat this is not a drill,” the National Weather Service said Sunday, urging people living below Oroville Dam to evacuate. The evacuation was ordered because of a “hazardous situation” involving the Northern California dam's emergency spillway. The National Weather Service said the auxiliary spillway is expected to fail and could send an “uncontrolled release of flood waters from Lake Oroville.”
DWR Press Release: February 12, 2017 6:20p.m.
EVACUATION FOR LOW-LYING COMMUNITIES
Oroville, CA — Based on information received from the California Department of Water Resources (DWR) and the incident command team managing Lake Oroville, counties and cities near Lake Oroville and the surrounding area issued evacuation orders for residents. The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville. Those potential flows could exceed the capacity of downstream channels.
To avert more erosion at the top of the auxiliary spillway, DWR doubled the flow down its main spillway from 55,000 cubic feet per second (CFS) to 100,000 CFS The next several hours will be crucial in determining whether the concrete structure at the head of the auxiliary spillway remains intact and prevents larger, uncontrolled flows.
Current flows are contained with downstream channels.
Flow over the auxiliary spillway weir began Saturday morning and has slowed considerably. DWR officials expect that flow to stop entirely soon, which will reduce the erosion on the downstream side of the structure.
Oroville Dam itself is sound and is a separate structure from the auxiliary spillway.
As I understand it, there is another major storm due this week.
Even with no more damage, it might not be safe for use as a more than half full reservoir for a long time—and it’s a very important reservoir. Now that’s a “shovel ready” project if I ever saw one. Will it takes years to approve repairs, fight lawsuits against repair, plan for, and then repair it? Hopefully not.
California can sure use the rain, but decades of building no new major dams to store rain and snowmelt means that most of it will run into the sea. Go bullet train to nowhere! Meanwhile, the Santa Barbara area remains in severe drought as a peculiar dry spot, though that might change this week.
At least in my area, the ground is super saturated. One modest temblor could cause major damage from mudslides and similar.