|
Thermistors will determine North Slope tundra opening 2003 travel study increased tundra opening; new standard of snow and subsurface temperature offers heads-up for seismic Kristen Nelson Petroleum News Editor-in-Chief
The Alaska Department of Natural Resources has changed the way it measures ground hardness for North Slope tundra openings.
The standard for opening the coastal plain last year was six inches of snow and 12 inches of frost, measured by a drop hammer, a test of ground hardness.
The new standard, based on results of the division’s tundra travel study, is based on snow cover and subsurface temperature measured by thermistors at 16 North Slope sites.
The division has been working on a more science-driven management of tundra openings since 1970 and since then its measurements have become increasingly sophisticated, Bob Loeffler, director of the department’s Division of Mining Land and Water, told an Alaska Oil and Gas Association project conference Oct. 19.
By 2000, he said, the division realized it needed to do something to address the shortened on-tundra work season, which had dropped from 200 days to around 100. In 2002 the division split the North Slope into four tundra opening areas and standardized measurement sites, standardized drop hammer measurements of tundra hardness and did a pilot study of effects “that indicated our management may, in fact, be too conservative.” Tundra travel study In 2003 the division began a tundra travel study with twin goals of increasing the winter work window and enhancing its ability to prevent damage to the tundra.
Loeffler said results of that study showed underground temperature to be a good measure of ground hardness, with minus 5 degrees Celsius about as hard as it gets.
In the coastal plain, or moist sedge tundra, 75 drops per foot on the hammer replicated minus 5 degrees C; in the tussock foothills area, 25 drops of the hammer per foot replicated minus 5 degrees C. That was the measurement the division used in 2004, based on results of its study.
“This year we’re going to a complete thermistor system,” he said.
A thermistor is an electronic device, Loeffler told Petroleum News. A piece of metal is inserted in the ground and measures the temperature. Based on results of its tundra travel study, the division is interested in the temperature 12 inches down, he said. Some of the devices at the 16 permanent stations are recording, he said “but none of it’s electronically transmitted,” so some data is downloaded and some of the thermistors are energized and read on the spot.
This year six inches of snow and minus 5 degrees C measured by thermistors is the coastal plain opening standard; in the foothills nine inches of snow and the same temperature is the standard, he said.
In 2002 the winter season was 104 days; last year, Loeffler said, based on standards from the 2003 study, “the winter season was 161 days.” Weather conditions were better, but Loeffler said a gain of 20-30 days can be attributed to the new standards.
Use of thermistors also allows some predictability, he said. The division found it takes about 10 days for the temperature to go from minus 1 degree C to minus 5 degrees C, allowing the seismic industry a heads-up for planning the beginning of the on-tundra season.
The situation with ice roads is different he said. There the emphasis is on pre-packing, which gives industry a 13 to 38 day advance to begin building its ice roads, and also offers further environmental protection with a lower level of tussock damage.
| 