Monday, February 13, 2017
The dam and spillway situation at Lake Oroville in Northern California are apparently severe enough to cause the evacuation of around 200,000 residents of the City of Oroville and towns downstream on the Feather River. Flooding is either happening right now or is expected throughout the Sacramento Valley thanks to heavy rains, saturated soils, and rivers and streams overflowing their banks.
The problems with Lake Oroville are on top of an already difficult situation.
I'm paying attention to this rather more than I might otherwise do because the region under flood warning and evacuation is part of my old stomping grounds in California. I lived mostly in and near Sacramento, but I traveled all over the Valley, particularly north of Sacramento, and my work often took me to the area under evacuation and flood warning. I got to know many people there and I still have friends in the area. So many people have been evacuated, and there is still risk to many more. It's a horrible situation for many whose peace of mind has been shattered and whose world is overturned. My sympathies are with them, though there's little I can do from out here in the Central New Mexican wilderness.
For now, it seems the situation has at least partially stabilized. The lake level is down enough (a/o Monday morning, c.. 3:00 am) that water is no longer flowing over the auxiliary spillway and the immediate danger of spillway erosion and collapse is mitigated. Releases are apparently continuing from the damaged main spillway, lowering the lake level enough to allow more runoff and snowmelt to enter. More rain is predicted for later in the week, and depending on how much their is, the situation could return to critical very quickly.
The problem with the auxiliary spillway as I understand it is that erosion of the upper part of the spillway has been severe due to the over-top releases yesterday and the day before; authorities are afraid that the erosion will compromise the integrity of the spillway and lead to collapse of that section of the lake-wall (not the dam itself). If that were to happen, an immense flood of lake water would be sent down the Feather River, almost as if the dam had broken, and people in the path of the flood would be at severe risk.
Because that risk is somewhat less now than it was yesterday afternoon, I'm sure people who have evacuated are fuming, thinking perhaps they shouldn't have been told to move so suddenly.
From the views I saw of the spillway yesterday, however, it was clear that the situation was developing fast and there was no certainty at all that the lip of the spillway would hold. Given the flood situation throughout the Valley already, it was reasonable to declare a precautionary emergency and to get people out of the path of any potential Lake-flood.
In the meantime, as chaos spreads, it's well to remember that flooding (though not this kind of threat) is relatively frequent in the area, and most residents are able to cope one way or another.
News is available at the Sacramento Bee, KCRA, and KNVN. There are other news outlets in the area as well, but these some of the main ones.