After posting “Ice Roads (1)”, I came across this article, courtesy of Alan Bailey at Petroleum News. It gives a little more detail.
Northern Alaska’s vanishing highways
Evolving ice road construction techniques are enabling oil companies to adapt to varying winter and tundra conditions. Alan Bailey – Petroleum News
Ice roads have proved to be the technique of choice for accessing remote North Slope drilling and construction sites for quite a few years now. But the monitoring of the impacts of these “vanishing highways” combined with some construction ingenuity are enabling people to refine the ways in which ice roads are constructed.
At a presentation to the Alaska Forum on the Environment on Feb. 11 Gary Schultz of Alaska’s Division of Mining, Land and Water described the results of a study into the effect of ice roads on the tundra. With increasing oil prices driving increased North Slope oil exploration and development, ice road construction has boomed in recent years, Schultz said. “Compared to a gravel pad and gravel road system … you can build ice roads that have very little (environmental) impact,” Schultz said.
Traditionally, companies have started ice road construction after the Alaska Department of Natural Resources has opened the North Slope tundra for winter off road travel. DNR’s criteria for the tundra opening ensure that there is adequate snow cover and a sufficient depth of frozen ground to ensure that vehicles will not damage the delicate tundra surface.
Once the tundra is open for travel, a first step in ice road construction is to break up the hard-pack snow along the road route, to ensure that the road ice forms a solid contact with the underlying tundra, Schultz said.
“For standard ice roads you want to have good contact between the water that turns to ice and the tundra,” Schultz said. “If you have air pockets in there the ice roads will end up breaking up when you start hauling heavy loads on it.”
A light water truck then sprays water along the route to create a thin layer of ice. Placement of a layer of snow and ice chips on the initial ice is then followed by the addition of more water. Then, once the primary road surface is formed, a heavy water truck can come in to add more layers of ice.
“Ice roads are really hungry for water,” Schultz said. “… A traditional ice road would take about a million gallons per mile of ice road.”
But increasingly short winter tundra travel seasons have resulted in a trend to start ice road construction before the tundra travel opening date. An early start to ice-road construction can extend the exploration drilling season and thus enable more wells to be drilled in a single winter season.
In the winter of 2002-03 ConocoPhillips built a one-mile section of demonstration ice road, starting the construction one month ahead of the tundra travel opening, Schultz said. That demonstration section formed part of a road to the Alpine field — the company continued to construct the bulk of the road after the tundra travel opening.
DNR could then compare the appearance of the tundra under the demonstration section with the impact of standard construction of the remainder of the road.
“We went out the following summer and we looked at measured impacts along the ice road route,” Schultz said.
Environmental consulting company ABR conducted a similar study for ConocoPhillips, he said.
In doing its study, DNR looked at three primary types of tundra: wet sedge, moist sedge and tussock. And the investigators found that the surface disturbance from the ice road was significantly different for those different tundra types.
In areas of wet sedge there was almost no impact on the tundra under either the demonstration road section or under the standard road. In moist sedge, on the other hand, the active layer of the tundra deepened to 5 inches in the demonstration section, compared with 2 inches on the route of the standard road section, Schultz said.
The ecological significance of deepening the active layer is not clear, although it may change the proportions of different types of cotton grass, Schultz said.
Tussock tundra underwent significantly more impact, with effects varying from no disturbance through to tussocks that were shattered and destroyed.
The investigators devised a system for categorizing the tussock impact using a scale of zero to three, with zero representing no impact and three representing shattered, crushed or removed plants. Then, by counting from one summer to the next the numbers of individual tussocks and the number of tussock land plots with different levels of impact, the investigators could systematically measure the ice road impacts and recovery of those impacts over a period of several years.
These measurements indicated less tussock disturbance under the standard road compared with the demonstration road section. But multi-year monitoring showed that after two to three years a significant amount of the level-two disturbance had dropped to a lower level of disturbance, while level-one disturbance disappeared in a similar timeframe. Monitoring of a more severe scrape in the tussocks suggests that that damage will take about 10 years to recover.
But people have made much progress in devising techniques for starting road construction early without causing detriment to the environment.
Essentially, it is possible to go out on the tundra prior to the winter tundra travel season using low-impact vehicles such as Rolligons that are certified for summer off-road use. These vehicles can pack the snow down along the ice road route, perhaps doing several runs along the route between periods of snow.
In general, pre-packing extends the ice road season by about a month and minimizes any impact on the tundra, Schultz said.
Packing the snow down reduces the insulating effect of the snow and thus accelerates the freezing and hardening of the ground as winter approaches. The packing also improves the uniformity of the freezing.
“You don’t have one area of the ice being adequately frozen and another area not being adequately frozen,” Schultz said.
Pre-packing also stabilizes the snow cover, to minimize the loss of snow during strong winds.
“In 2004 in the Alpine ice roads, the wind blew all the snow away except for where they’d gone out there and pre-packed,” Schultz said.
Pre-packing can be augmented by the side casting of water onto the road route from a Rolligon.
And poor snow cover at the start of the last couple of winters has led to another pre-packing technique that involves spreading a layer of snow and ice chips from lakes along the road route. Water can then be sprayed into the road surface to form the solid ice road structure.
“They did a great job with it (last year) and there was very little impact,” Schultz said.
So, are there any lessons to be learned from all of this on the optimum road construction methods?
First of all, route selection is important because of the differing sensitivities of different type of tundra to ice road construction.
“It’s good to get out there in the summer when you can see what kind of vegetation there is and stake the ice road at that time, and avoid the tussock tundra if you can,” Schultz said.
And the heightened sensitivity of tussock tundra to ice road construction leads to the perhaps surprising result that ice roads have the least impact in areas of wet sedge tundra — conventional wisdom tends to regard wet areas as being especially sensitive to environmental impacts.
Pre-packing, although expensive, pays dividends in protecting the tundra while also extending the ice-road season. But, especially in the early stages of road construction, experience has shown that highly skilled machine operators can reduce the likelihood of accidental tundra damage.
“When you’re in the pioneer phase of the ice road get the best operators that you can,” Schultz said.
It’s also important to change the road routes from one winter to the next, at least on tussock tundra, to give the tundra an opportunity to recover from a previous year’s road construction, Schultz said.