Skip to main content

Surveying the Sierra snowpack

March 1, 2011

Los Angeles Department of Water and Power hydrographers weigh an empty tube, called a tear, used for surveying snow at the beginning of the day. Dustin Taylor wears the scale around his neck and does the data entry, while Brian Norris carries the tube. Photo by Mike Bodine

The air is crisp at Tom’s Place at 8 a.m. The slight breeze blows around ice crystals, dazzling in the sun light, tiny floating prisms. Drips of coffee freeze to the side of the mug.
“Do you have extra clothes? Bring all you’ve got,” says snow-surveyor Brian Norris, “It’s cold up there.”
It only takes a few minutes outside of the car to numb fingers, cheeks and nose and there’s still another 3,000 feet to go up to the first survey spot.
But for Norris and Dustin Taylor, hydrographers for the Los Angeles Department of Water and Power, this is just another day on the job. It’s the monthly trek up Rock Creek to check the snowpack. This is one of four snow survey courses that DWP has used since it first started keeping track of snowpack in 1926. The other three are Cottonwood Canyon, Big Pine Canyon and Mammoth Pass. A course is about 1,000 feet long with a set series of markers or poles, about 100 feet apart. These courses are followed year after year.
In fact, this is the very course Taylor’s father, uncles and great-grandfather followed as surveyors for the department. Taylor’s a fourth generation snow surveyor, and the fifth working with the department.
The lure of the job is obvious for anyone who enjoys the outdoors. Beyond wanting to carry on the family tradition, Taylor said, he gets paid to have fun – drive a snowcat and snowshoe to remote spots in winter and spend summers around creeks and rivers checking gauges and flow.
Norris and Taylor are a part of the larger team that determines how much snow and water is in the Sierra backcountry.

History of Surveying

The Sierra Nevada range has been compared to giant wells, holding water in the winter as snow and ice that melts in the spring and summer, providing water for a large swath of people and agriculture.
According to DWP, approximately 65 percent of the water for the City of Los Angeles and its 3.5 million inhabitants comes from Eastern Sierra surface water runoff. Water runoff to the west side helps support the agriculture of the Central Valley which produces more than 20 percent of the nation’s supply of cheese and milk and more than 50 percent of the nation’s fruits, nuts and vegetables.
The science of snow surveying in the Sierra is more than 100 years old. Dr. James Church of the University of Nevada at Reno began measuring snow in 1906 on Mount Rose. Church was studying the relationships between snow content and water runoff. In the process, his measurements helped settle disputes between landowners near Lake Tahoe and those downstream by regulating runoff, preventing waste and flooding. Church’s techniques are still in use today.
Now, in addition to crews on the ground, such as Taylor and Norris, taking manual measurements, there are water content transducers and ultrasonic depth sensors to give as accurate a survey as possible.
The attention to detail is evident when Norris and Taylor get ready for their first course. The first of the day, the upper course, is at an altitude of approximately 10,000 feet, just west of Rock Creek Lake.

The Survey

Before getting out of the cab of the new Pisten Billy Scout Snowcat, Taylor takes a few passes with the blade to create a platform to stand on and put on snowshoes. The tops of road signs barely poke out above the powder.
Taylor is the recorder and Norris will be doing the snow drilling for this course. Taylor wears a hooked scale around his neck and carries a notebook in one hand. Norris screws together the three-foot aluminum tubes used to poke in the snow and collect core samples. The tubes are calibrated with inch marks and have slits cut in the sides to provide views of the ice and snow layers.
Before heading out, Taylor makes a tear, or weighs the tube empty. When a core sample is taken and weighed, the difference in weights determines the water content of the snow pack. Tears are done at the beginning, middle and end of a course. Taylor explained that as the day wears on and the tubes warm, water can collect on the sides of the tube and increase its weight.
Norris breaks trail to the first stake of the survey. Norris is careful that he takes measurements from the same side, east or west, of the pole every time. The surveys start in January, and are done once a month through March. His first survey is done away from the post and each month he moves closer to the post. He says he does this to get a clean sample every time in a spot that has not been unnecessarily packed down or trampled by the surveyors themselves, and to avoid mistakenly hitting the same hole two times in a row.
Norris drives the pole into the powder, shoving down hard enough to hit dirt, but not too much. He jerks the pole out quickly and checks to see if he’s hit bottom – looking for dirt or PNND, pine needles and duff. He notes to Taylor the snow depth, and the core depth, which is the amount actually in the tube.
Taylor takes a stick and carefully scrapes out the bit of earth stuck in the end and then measures how much has been scraped away. The amount of soil can vary from none to two inches depending on the ground, and that amount is subtracted or “cut” from the initial measurement.
The tube is then weighed. The weight of the tube is subtracted from the weight of the full tube to give a reading of water content. At the first post of the upper course, the filled pole weighed 63.0 and the tear was 50.5. Then the two weights are subtracted, leaving 12.5 inches of water content at that point of the course.
Chris Plakos, public information officer for DWP, said mathematical formulas have been created based on the poles and their weight in order to calculate the measurements and come up with an amount of water in inches.
Norris keeps the snow in the tube while he snowshoes to the next marker. He said the snow doesn’t stick in a cold tube. As the day progresses and the poles heat up in the sun, it becomes harder and harder to get the snow out of the tube. Sometimes Taylor has to hack at the end to try and loosen it. When the snow and ice start to stick to the inside of the tube, Taylor busts out the “rat.” The rat is a lightly greased rag tied to a long string; a weight is tried on the other end of the string. The weigh is pushed through the tube then, with a tug of the string, the rat is pulled through, cleaning out the pole.
Through the three courses of the day, measurements varied widely. However, according to Taylor and Norris, this is normal considering the inconsistency of snow depths due to blowing or drifting snow, proximity to trees and other vegetation and amount of sunshine received at a spot.
The second course is a survey at the snow pillow next to the Rock Creek Pack Station.
The pillow is a large rectangle of four, four-foot square steel plates. The plates are welded together with an antifreeze inside the layers. When snow falls, the antifreeze is pushed out into a pressure sensor that then coverts the amount of snowfall to water content.
The pillow is also the spot of a minimalist weather station, recording water content of the snowpack, temperature, wind and solar radiation. There is an ultrasonic depth sensor above the pillow. All of this information is transmitted to California Department of Water Resources in Sacramento via satellite.
This wealth of information is used to gain the most accurate and detailed water content survey available.

The Results

Plakos explained by phone that numerous agencies throughout the state, public and private, with snow courses just like the one at Rock Creek are taking similar measurements. The data is given to the Water Resources Department and used to make predictions and forecasts.
These numbers are used by DWP to produce “precipitation averages,” Plakos said. These averages are based on 50-year averages.
“It’s in both the public’s and government’s interest to know what the conditions are, what to expect,” Plakos said.
The department publishes graphs of current snow water content and precipitation conditions in the Eastern Sierra at http://www.ladwp.com/ladwp/cms/ladwp006428.jsp.
According to the most recent graph, as of Feb. 22, the Rock Creek snow pillow read 18.7 inches, or 187 percent of normal. Mammoth Pass has 44.1 inches of water, consistent with an average year.

Premium Drupal Themes by Adaptivethemes