Major rains along with record snow pack could amount to danger

California has not seen rain like we're having in many years. That's extremely helpful to filling the Golden State's water starved dams; especially the major mega dams tens of millions of Californians depend on. But, with precipitation, too much of a good thing requires intense oversight and management, round the clock, by reservoir and dam operators.

Most major California dams have two main purposes. One: hold as much water as possible for use when rains end. Two: prevent downstream flooding by not releasing too much water in rainy season when creeks and rivers are high while still leaving enough room in the reservoir for incoming storms.

Joshua Viers, a watershed scientist at UC Merced. "It is a delicate balancing act, and it's one that I think keeps a lot of engineers up late at night," said Professor Viers.

The disastrous 2017 overtopping of the Oroville Dam was a direct result of three massive storms, over a short period of time. It overwhelmed the dam's ability to safely hold and safely release water, severely damaged it and destroyed its spillway. A hundred and eighty-eight thousand people downstream were evacuated  

That was then. This is now.

Professor Noah Diffenbaugh, A Stanford University Climate Scientist. "This is a really long string of storms that we've had. Climate change is affecting that both in terms of the intensity of precipitation and also how much rain versus snow we get during storms and at what elevations," said Professor Diffenbaugh.

Besides the chain of storms themselves, California's record snow pack, 225% above average so far, could be big trouble for dams and reservoirs if it gets too warm or if warm rains fall on it and melts it too soon.

Yes. This is all about a changing warmer climate. "That rain on snow event can actually mobilize a tremendous amount of water in a short period of time that we've seen to be catastrophic," said Viers. "It takes time to release water from those reservoirs to create additional space," said Diffenbaugh.

Once again: a high stakes balancing act. "Often times, we have to release a lot more water from these reservoirs in anticipation that there might be more rain to come," said Viers. "Inherent in our system is this, you know, this balancing act," said Diffenbaugh. 

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Example: essentially full, Lake Mendocino. It has only enough space left to try to prevent flooding on the already swollen Russian River. "Our Army Corps of Engineers controls that flood pool. So, they'll see when that water needs to be released to obviously protect at the dam," said Andrea Rodriguez, Somoma County Water Agency’s spokesperson.

At the same time, climate change is accelerating. "The three highest flows that we've ever recorded in the last 115 years, have all occurred in the last 25 years," said Viers. A balancing act indeed.