Operators ready reservoirs to hold large snowpack


Issue Date: April 12, 2017
By Christine Souza
In operating Don Pedro Reservoir, the Turlock Irrigation District says it wants to supply farmers with the irrigation water they need while carrying over as much water as possible for the future.
Photo/Turlock Irrigation District

As Gov. Brown declared an official end to the California drought emergency last week, reservoir operators continued preparations to handle runoff of a Sierra Nevada snowpack that stood at roughly 170 percent of average at the start of the week.

The governor's order maintained water-reporting requirements and prohibitions on practices such as hosing off city sidewalks and irrigating ornamental turf on public street medians. It also ordered state agencies to continue requiring agricultural and urban water suppliers to "accelerate their data collection, improve water system management and prioritize capital projects to reduce water waste."

At the California Department of Water Resources, State Climatologist Michael Anderson said recent "cold air" storm systems brought "rainfall all of the way from Los Angeles up to the Oregon border, with more accentuated values in the mountains both on the coast and in the Sierra Nevada."

The April storms will "augment that snowpack a little further," Anderson said, "which means it should hang in there further into summer and give us more water that we can manage."

Managing the water falls in part to reservoir operators around the state such as the Turlock Irrigation District, which maintains Don Pedro Reservoir, a joint project of TID and the Modesto Irrigation District.

TID Assistant Manager of External Affairs Michelle Reimers said the reservoir on the Tuolumne River is experiencing a "historic water year."

"The snowpack is double the amount that we usually have, and we have a pretty full reservoir," Reimers said, "plus, we're still in flood-control space. Right now, we're running full tilt."

That means improved water supplies for farmers in the two districts.

Officials from MID, which kicked off its irrigation season with a 42-inch-per-acre water allocation, said that based on the snowpack in the Tuolumne River watershed, increased releases are likely to continue through the summer and perhaps beyond. Likewise, TID is supplying irrigators with a water allocation of 48 inches per acre, or the maximum amount of water, with the opportunity to purchase additional water.

TID noted that the Tuolumne River watershed has a projected 2.235 million acre-feet of snowpack. Recent storms were expected to bring up to 11 inches of rainfall to the Tuolumne River watershed, which is about 550,000 acre-feet of expected runoff, or about 200,000 acre-feet above the average runoff.

In February, saying it needed to maintain space to capture anticipated runoff, TID opened the spillway at Don Pedro.

"Our main concern is getting through this spring without having to open the spillway again," Reimers said. "A second concern would be to make sure we have full carryover for next year, which looks like that will be the case. Our whole goal is to supply our farmers with as much water as they need and also carry over as much as we possibly can without carrying over into the flood-control space. It looks like we will be able to do that this year for the first time since 2013."

Reimers and other water officials have expressed concern about warm spring temperatures rapidly melting the snowpack, causing too much water to run off into the water system.

"We have a ton of water and we are watching very closely, all of these storms," Reimers said. "What is really important is the temperature of these storms."

With days getting longer, this is the time of year when the snowpack begins to melt. At DWR, Anderson pointed out that, starting this month, "I think we're going to see the storminess drop off and the warm weather start to increase."

"Mid-May is when we tend to get the peak of the snowmelt, and from there it is just melting off at an even pace as the snowpack decreases," he said. "That tailing off goes all of the way through July, but this year, we will have water feeding into the reservoirs all of the way into July, which is fantastic. We haven't seen that since 2011."

As it manages water in California reservoirs, DWR is also trying to ensure there is enough room for flood control, Anderson said.

"The challenge has been we had so much water in the winter, particularly in the San Joaquin system, they are really constrained in how much water they can release from the reservoirs, so they have to release as much as they can for a very long period of time," he said. "Aside from the extremes that we had to navigate during January and February, we have the abundant snowpack that we were hoping for and it's looking like it will melt off in a rather well-behaved manner."

(Christine Souza is an assistant editor of Ag Alert. She may be contacted at csouza@cfbf.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.