Despite the relatively wet characterization of snow, data extracted from this month’s snow course measurement has revealed wintry powder throughout the Tuolumne Basin to be momentously dry.
“The March 1 snow course measurements this year are significant in how dry they reveal the snowpack to be,” said Turlock Irrigation District utility analyst Jason Carkeet. “This year, the basin water content is approximately 17 percent of the historical average.”
According to Carkeet, snow course measurements are used to determine the water content in snow at a given location, one of which is the Tuolumne Basin.
To extract core samples of the snow pack, the California Cooperative Snow Surveys Program utilizes metal tubes over the course of a few days surrounding the first of February, March and April.
Once the samples are secured, they are weighed to determine their water content, which is expressed in inches of water, otherwise known as the Snow Water Equivalent.
“One way to think of the water content in terms of inches of water is to imagine taking that core sample of the snow pack, melting it down, and measuring how many inches high it would fill the same sampling tube,” explained Carkeet.
This month’s measurements also reveal that higher water content is evident at higher elevation snow courses near 9,000 feet, however, Carkeet reports that this does not necessarily apply to the Tuolumne Basin, as only 15 percent of the watershed is at or above 9,000 feet elevation.
“The thing to remember is that the higher the elevation, the less of a percentage of the watershed that is represented,” said Carkeet.
After all snow course data is calculated, the Department of Water Resources has the ability to produce runoff of water supply forecasts for each of the basins included in the CCSSP. Each forecast is issued near the beginning of the month, followed by a weekly update that reflects up-to-date precipitation data.
“Whereas electronic instruments can sometimes fail, snow course measurements are important because they are physical, observable samples of the snowpack,” said Carkeet. “The data produced are a large part of the input for the water supply forecasts produced by DWR.
“Granted, they are only a part of the picture when looking at the snow pack and trying to predict water supply by various means, but they are a significant part of that picture,” Carkeet continued.
This month’s significantly dry snowpack will undoubtedly play a role in this year’s irrigation season—the starting date of which is still up in the air.
“It’s up to the Board of Directors to set the date to start irrigation and the amount of water available,” said TID spokesperson Calvin Curtin. “As of today, we are anticipating recommending to the Board a start date of April 9. Of course, if weather ends up either extremely wet or extremely dry, that date could change."
At a number of grower meetings in January, Turlock Irrigation District assistant general manager of water resources Tou Her revealed that his department could also potentially recommend an irrigation cap of less than 18 inches—a number that is dependent on whether the region experiences an additional 10 inches of rain falling in February and March.
During his water report on Tuesday, Carkeet revealed that accumulated watershed precipitation throughout the month of February up until March 1 was 4.25 inches.
The district also said during the January meetings that they are planning to pump 90,000 acre feet of groundwater for the 2015 season, 30,000 acre feet more than last year. Although planning to rent more pumps than ever before, pump owners in one area of the district will not be asked to help out.
Her said that due to efficiency concerns, the district would not be renting pumps located in the northeast quadrant — east of Faith Home Road and north of Harding Road. However, those pump owners will receive information on pumping for credit.