Replies

There’s 25 million+ acre feet of water in the form of snow in the Sierras as of the last reports, this has likely increased with multiple days of snowfall, and will gain even more this weekend.

To put that into perspective, the California central valley is roughly 7 million acres. If it was exactly flat, that means about 3’7” of water for every single square inch of the central valley. As it isn’t flat, and quite a number of people live along the rivers in the central valley, there will be prolonged and severe flooding.

Some of the previous high water marks for Don Pedro occurred not in the middle of heavy winter rains but in August when some late July summer rains melted considerable reserves in the sierras. There are a number of ski resorts which have issued ski passes for 4th of July weekend; they’re extremely sure that they’ll be still open then.

IF northern California gets one or more ‘atmospheric river’ events, that of a warm and very wet stream of moisture, it could easily slice into that huge snowpack and cause quick and sudden melting. That 50 feet of available space in places like Oroville Dam could be filled within a day and a half.

The emergency spillway they destroyed with minimal flow was designed to mitigate sudden snow melt, sending a sheet of water like a ski jump, high into the air and to fall much further down the hillside.

So, anyway, yes, there can be serious flooding from snowmelt, and absent dam managers emptying out reservoirs to much more sane levels, the flooding will be prolonged and intense.

Just to put everything in perspective: the Governor’s Mansion in Sacramento was raise to 3 floors after the prolonged floods of 1861 drowned the city in 10 feet of water for nearly 4 months. Dams like Oroville, Don Pedro, Shasta, etc were designed not just for water storage and distribution, but also as a regulator for snow melt and hydro-logic events.