Operators of Oroville Dam – the nation’s highest – shut down its main spillway Monday so that debris could be cleared and the dam’s hydroelectric turbines could be restarted.
It was merely the latest of many operational adjustments state and federal officials have made this year to cope with an unprecedented series of rain and snow storms that swept through the state, putting maximum pressure on its complex system of dams, reservoirs, river channels, canals, bypasses, weirs and other man-made water-control devices.
By necessity, they operated on the fly as conditions changed, often suddenly, with Oroville being the centerpiece.
As heavy runoff from the Feather River’s vast watershed pushed Lake Oroville’s level sharply upward, operators increased outflow on its concrete spillway, only to see portions crumble.
The outflow was reduced, even briefly to zero, to prevent further damage, but when tropical storms melted snow at lower elevations, inflow quickly rose to 1.5 million gallons every second. The lake reached maximum capacity and a never-before-used emergency spillway automatically began flowing.
However, the hillside below the emergency spillway was “unarmored” dirt, for the most part, and it quickly eroded – so much so that dam operators worried that the lip of the spillway would collapse, sending a destructive wall of water racing down the Feather and endangering nearly 200,000 people in several downstream communities.
Authorities ordered immediate evacuations, and the roads filled with refugees. Meanwhile, Oroville’s operators increased releases on the damaged main spillway to lower the lake below the emergency spillway’s lip.
It worked. The main spillway has held, more or less, and the lake has been lowered 63 feet – enough, along with drier weather, that the Department of Water Resources could shut down the main spillway again for much-needed channel clearance.
What happened – or didn’t happen – at Oroville was just the most dramatic example of how professional water managers, both state and federal, and emergency personnel have made hour-by-hour adjustments to cope with heavy flows and will continue doing so as the massive snowpack melts.
Another example: Folsom Lake on the American River has been lowered to less than half its capacity, angering some nearby residents. But federal operators know there’s a heavy snowpack that will melt and want enough space in a too-small lake to handle it without flooding.
Have water managers performed perfectly? Of course not. They’re fallible human beings. But they did the best they could under constantly changing conditions and averted what could have been a massive disaster by making decisions whose outcomes could not be fully predicted.
Gov. Jerry Brown paid brief homage to the state’s water managers during a press conference last Friday, calling the circumstances – accurately – “quintessentially expert kinds of things” and adding, “We have a very expert Department of Water Resources.”
Yes, we do.