Tundra Travel Management Strategy

December 2, 2004

The Problem:
A serious problem is confronting oil exploration in this state: the winter oil exploration season is becoming ever shorter. The Department of Natural Resources, Division of Mining, Land and Water (DNR) opens the North Slope tundra to exploration when the ground is frozen enough that companies can explore over snow without significantly damaging the tundra. But these openings were coming later and later because of warming weather, regulatory changes, and changes in measuring techniques. In fact, the winter exploration season has been effectively cut in half since the early 1970s.

Shorter seasons have serious consequences to those who are trying to get the work done. It's also a problem for oil production that relies on the exploration, and for Alaskans who rely on the oil industry: in other words, for all of us. We need to lengthen the season, but we need to do so in a way that respects the environment.

Solving the Problem:
To solve this problem, DNR worked with the US Department of Energy to develop scientifically valid, peer-reviewed research to find ways to extend the season without compromising the environment. The study focuses on advancing opening dates because 85% of the lost season length is due to later opening dates. The study analyzes the changes on tundra test plots when various equipment used for exploration were driven on the plots during various stages of tundra freeze up and snow conditions. Much data has been collected from the test plots over the course of a year and half. The results give us a statistical model of what expected tundra disturbance will be experienced as the result of using various vehicles in certain conditions.

Now that the study is complete, this document addresses how DNR will incorporate the results into management decisions for the 2004-2005 winter work season. The results are supportive of lengthening the oil exploration and development season by providing an earlier tundra opening date. This document also explains the transition from historical tundra opening standards to new standards based on actual environmental conditions that are scientifically related to limits of disturbance.

General Overview of the Study Results:
The DNR Tundra Model project found that the hardness of frozen ground, the depth of snow cover, and the formation of hard snow slabs within the snow profile influence resistance of tundra to disturbance by hydrocarbon exploration vehicles, depending upon the vegetation community type. Also identified in the study were certain trends in the development of winter time conditions of these ground and snow characteristics that may be useful in interpreting the data to assist management decisions.

Engineering literature cited in the study suggests that hard frozen ground resists compression and ductile deformation. The hardness of the ground increases with lower temperature, to a certain point, after which frozen soil may be subject to fracture failure. The data from the study sites, as well as that from the existing scientific literature, suggests that the freeze-up and hardening of tundra ground exhibits a statistical sinusoidal pattern in both the Coastal Plain and Foothills regions of the North Slope. This means that there is a slow advent of ground hardness, followed by a rapid increase in hardness, quickly tapering off to a slow increase in hardness as winter progresses. Soil freeze up occurs from two directions within the active layer. The first advance of ground freezing occurs at the bottom of the active layer (nearest the permafrost) towards the surface. After a several week lag time, air temperatures are sufficiently cool to begin freezing the ground from the surface down. Temperatures remain fairly constant within the soil profile for a period of two to four weeks as the latent heat of soil water tempers the change in soil temperature. Once freeze up is complete, the soil temperature drops markedly, leading to a quick increase in ground hardness.

Once the hardness of the ground reaches this point, represented by the top inflection point on the statistical sinusoidal curve, the functional contribution of further hardness to resistance plateaus. Thus, it appears no additional benefit in terms of increased resistance to deformation/compression disturbance is realized through further cooling of the ground.

Data from the University of Alaska Fairbanks Geophysical Institute seems consistent with this observation. Soil temperature arrays located within 1/8 mile of the coastal/wet sedge study site and 1/8 mile of the foothills/tussock tundra appear to show a similar freeze-up pattern in the top foot of soil (See Table 1a,b).

According to results from the DNR study, the point at which functional hardness reaches a plateau seems to be at approximately 75 drops per foot of ground penetration with the DNR slide hammer in wet sedge meadow tundra and 25 drops per foot of ground penetration in tussock tundra (See Table 2 a,b). As shown in these tables, there was an accelerated freezing of the ground with corresponding increase in ground hardness between November 13 and December 4. There was also a marked decrease in the rate of change after December 4.

Table 1: Soil Temperature by Test Date in a One Foot Profile (Temperature expressed in degrees Celsius at cm depths).

a. Coastal Plain/Wet Sedge Study Site

 

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

15 cm

-0.42

-1.49

-6.21

-8.01

-8.15

-14.72

23 cm

-0.28

-0.88

-5.25

-7.65

-8.01

-14.19

30 cm

-0.13

-0.38

-4.34

-7.28

-7.87

-13.66

b. Foothills/Tussock Tundra Study Site

 

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

10 cm

-0.52

-2.46

-7.42

-7.62

-12.34

-10.22

18 cm

-0.08

-1.31

-6.51

-6.78

-11.50

-9.95

30 cm

-0.04

-0.71

-5.49

-5.95

-10.57

-9.86

Table 2: Ground Hardness by Test Date (Hardness Measured by Total Slide Hammer Drops to Penetrate One Foot of Ground � dpf)

a. Coastal Plain

Date

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

Hardness

11 dpf

27 dpf

74 dpf

89 dpf

83 dpf

105 dpf

b. Foothills

Date

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

Hardness

3 dpf

4 dpf

25 dpf

23 dpf

18 dpf

25 dpf

Snow deposition on the North Slope exhibits a bimodal pattern with heavy snow early in the winter, followed by a long period of cold dry conditions. Snow fall accumulation increases again late in winter near the onset of spring with the renewed appearance of relatively humid air masses. A stable snow depth that averaged 15 to 18 cm was present over wet sedge tundra throughout the study period; an average of about 23-25 cm of snow was present throughout the study in the tussock tundra. The available literature suggests that snow depth protects the tundra surface from mechanical disturbance. However, lack of variability in snow depth over the course of the DNR study prevented a thorough investigation of the degree of contribution increasing snow depth provides. It does appear, though, that the level of snow during the study experiments did make a substantial contribution to disturbance resistance. What the minimum threshold is, and what level provides the maximum contribution, is unknown at this time, but by requiring the average minimum that was present for the study allows us to predict the tundra resistance. (See Table 3a,b).

Table 3: Average Snow Depth by Treatment Date and Study Site (cm)

a. Coastal Plain

Date

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

Snow

15.24

12.58

16.00

15.52

16.03

18.65

b. Foothills

Date

Oct 30

Nov 13

Dec 04

Dec 18

Jan 05

Jan 20

Snow

23.28

27.96

22.21

29.77

28.7

27.88

Finally, the model found that snow slab thickness provided a significant contribution toward tundra resistance to disturbance. The thicker the snow slab, the less the degree of change recorded in depth of active layer and change in soil moisture. No minimum threshold was found.

Tundra Opening Criteria
DNR intends to specify tundra opening criteria that will achieve the same level of environmental protection realized over the course of the last 10 years. DNR was able to model anticipated levels of change with differing combinations of snow and ground characteristics. After a review of study results and the available scientific literature, DNR has established the minimum combination of ground and snow conditions which are needed to achieve the level of protection that past year's openings provided for the tundra for both major ecosystems, the wet sedge tundra and the tussock dominated tundra. Last year, DNR opened the East Coastal Tundra Opening Area December 23 rd , West Coastal Area January 9 th , and the Lower and Upper Foothills on January 28 th .

Criteria:
DNR will implement tundra opening for general cross country travel in wet sedge tundra when a minimum 15 cm (6 inches) of snow cover is available and ground hardness reaches a minimum of 75 drops of the slide hammer to penetrate one foot of ground. At this combination of ground and snow conditions, no significant change in the depth of active layer, soil moisture, or vegetation composition and structure is anticipated.

DNR has determined that once a minimum threshold of 23 cm (9 inches) of snow cover and a ground hardness of 25 drops of the slide hammer for one foot of soil penetration has been attained, general tundra opening in tussock tundra can proceed without a significant change in active layer depth, soil moisture, or vegetation community composition and structure.

Although snow slab thickness has a significant effect on disturbance resistance, there was not sufficient data to thoroughly explain the relationship. In order to collect more data, DNR now requires the northern region staff to measure snow slab thickness as a routine part of its North Slope field measurement protocols. With additional data, DNR will evaluate its decision matrix to determine if snow slab thickness can be effectively incorporated.

By identifying combinations of snow and ground hardness characteristics and attendant disturbances associated with overland travel, DNR believes it can effectively ensure a level of protection for tundra resources equal to or greater than that attained under previous management while increasing the time available for overland travel. For example, were conditions across the North Slope last year like those found in the study sites, DNR is confident it could have opened tundra to off road travel on December 4, 2003 and still attained the environmental protection benefits realized by the more traditional dates. As a result, this could have increased exploration time by up to 45 days without any increase in environmental disturbance effects.

Monitoring
It is imperative to verify this decision with real time field monitoring to determine the accuracy of the model. Therefore, DNR employees will accompany initial deployment of vehicles at the time of general tundra opening for subsequent measurements regarding disturbance consequences. As a result, DNR staff will field verify disturbance levels associated with this management approach in the summer of 2005. These monitoring requirements must be a part of the authorization pursuant to this management strategy. In addition, we will continue to monitor the sites over several years to assess the resiliency of the tundra.

For more information contact

Wyn Menefee
Division of Mining, Land and Water
Phone 269-8501
Email: wyn_menefee@dnr.state.ak.us

 

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