March wasn’t exactly miraculous this year but it did OK by California’s snowpack, bringing it from a dismal 40-ish% of average up to above 60% of average in the northern Sierras.
The bump wasn’t so great in the southern Sierras where snowpack is still at 40% to 46% of average for the Kaweah, Kern and Kings river watersheds, according to Department of Water Resources runoff forecasts compiled as of March 24. The Tule River watershed is clocking in at a dire 27% of average, according to the DWR forecast.
Meanwhile, in the center of the state, March storms left a watershed a cliffhanger on the San Joaquin River.
Per a 2006 legal settlement, the river gets more or less water for environmental “restoration flows” depending on the type of water year.
“We’re right on the knife’s edge between a critical high or dry year,” explained Peter Vorster, a hydrologist and hydrogeographer with The Bay Institute, a party to the San Joaquin River settlement agreement.
Critical flows
A critical high year is actually drier than a plain old dry year, which means the river gets less water in critical high years, per the settlement.
The goal of the restoration flows is to keep water in the San Joaquin all the way to the Merced River in order to bring back native salmon populations, which once flourished in the river. The San Joaquin was dried up in the early 1950s after Friant Dam was constructed and almost all the river water was directed to towns and farms in the south via the Friant-Kern Canal.
“In a critical high year, we’re hanging on to every drop just to keep the river connected,” Vorster said.
The river gets about 71,000 acre feet for restoration flows in a critical high year. In a dry year, it gets 155,000 acre feet — a huge increase.
To conclude the year type, the Bureau of Reclamation uses snowpack survey data, plus runoff forecasts and calculates what the unimpaired flow of the San Joaquin River would be if Friant Dam and other structures had never been built.
All of that has to add up to more than 669,000 acre feet for a dry year. As of March 20, the Bureau calculated the unimpaired flow at 670,000 acre feet, just a hair over the threshold, Vorster explained.
Dueling forecasts
At the same time, runoff forecast models by DWR and the National Weather Service are giving vastly different information. DWR is predicting about 100,000 acre feet less runoff than NWS.
Without greater confirmation of a dry year type, the San Joaquin River Administrator has said he will manage the river’s flows as if they are in a critical high year in order to hold enough cold water at the base of the Friant Dam for salmon to get through the hot summer months, Vorster said.
Vorster and others are hoping that the April 1 physical snowpack check by DWR combined with data from the Airborne Snow Observatory (ASO) — along with more snow from a few incoming storms — will put the San Joaquin River watershed solidly into the “dry year” category.
Tech to the rescue
Vorster felt this kind of nail biting over how to manage key portions of the state’s water resources could be alleviated by a full commitment by the state, feds and water contractors to fund regular ASO flights.
ASO flights started as a joint project between NASA’s Jet Propulsion Laboratory and DWR using LIDAR, light detection and ranging technology, along with imaging spectrometry, to measure the depth and weight of snow across large watersheds.
The Friant Water Authority was an early participant in ASO flights, with its members chipping in to pay for regular surveys of the San Joaquin River watershed starting in 2017.
It’s not cheap at about $90,000 per flight. And it has drawbacks, such as no flights on cloudy days.
And it makes more sense for larger, more remote watersheds that don’t have adequate storage, said Kern River Watermaster Dana Munn.
In Kern County, where Isabella Lake at full capacity can store 570,000 acre feet and average runoff of the Kern River is 450,000 acre feet a year, ASO makes less sense than the San Joaquin River watershed where Millerton Lake can only store 540,000 acre feet and runoff can be three times that amount, Munn said.
“There are some spots where ASO makes sense, but it’s pretty expensive,” he said.
Where information from physical checks and scattered snow sensors is spotty, the ASO information can be an invaluable data bridge.
“It would be awesome data to have right now,” said Steve Haugen, watermaster for the Kings River when interviewed before the March storms. “We have 10 snow sensors in our watershed, which is a million acres. That’s not a lot of data points to draw some pretty big conclusions.”
The ASO information wouldn’t just help in dryer years, like this one, but it would be a huge help in potential flood years for dam operators to know how much water to expect and how fast.
“It’s beyond the research point,” Haugen said. “It’s ready to roll.”
He estimated it would cost $15 million a year for enough ASO flights to cover watersheds from Kern to Trinity.
So far, there haven’t been any successful attempts at funding legislation.
