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Wet winter produces record-breaking runoff
don pedro spills pic1
The snow is expected to continue melting at high volumes, making the 2016-2017 water year the highest runoff year on record. - photo by Journal file photo

Thanks to recent months that saw plenty of rainfall, the Sierra Nevada snowpack is currently holding 1.9 million acre feet of water content – and that’s after the month of April produced nearly a 100 percent increase in acre feet of runoff from April of last year. The snow is expected to continue melting at high volumes, making the 2016-2017 water year the highest runoff year on record.


The main months that see snow melt are April, May, June and July, according to Turlock Irrigation District utility analyst Jason Carkeet, but right now – the end of May – to around mid-June is when peak snow melt numbers occur. Despite the above-average amount of melting snow, Carkeet stated that flooding is not something that should be anticipated near the Tuolumne River.


“Because there is so much snowpack, we’re keeping total Don Pedro releases high,” said Carkeet. “With high flows, we try to keep the river within a narrow range so it’s not moving wildly, and you’ll start to see the river slowly come down as irrigation numbers go up.”


TID made 48 inches of surface water available this irrigation season thanks to both record rainfall in the region and the incredible amount of snow in the mountains. As of Friday, the average snow water equivalence in the Sierra Nevada snowpack was reported at 29.2 inches.


Snow water equivalence roughly equates to the amount of water that would hypothetically result if the entire snowpack suddenly melted. The snowpack on average provides about 30 percent of California’s water once it melts in the spring and early summer, and the greater the snowpack, the greater the runoff into California’s reservoirs.


In April, the Tuolumne River Watershed saw 526,000 acre feet of runoff. According to Carkeet, a typical April yields 270,000 acre feet of runoff. It’s impossible to know how much more snow will melt, but just over 4.6 million acre feet of runoff is the most on record, which occurred in 1983. Carkeet anticipates that this year, there is a 90 percent probability that the runoff will be equivalent to the amount recorded in 1983 or greater.


“There are pretty high odds that this could be the highest runoff year on record, and the record goes back to 1897,” said Carkeet.


Because TID is closely monitoring water levels at Don Pedro, the large snowpack may only result in somewhat increased flows in the Tuolumne River – no flooding.



“It’s good because we’ll have a full reservoir,” said Carkeet. “But, there’s no need to head for the hills.”