Tactic P-4: Minimizing Physical Damage to Tundra
Cleanup of a spill on tundra almost inevitably results in some degree of physical damage, caused by one or more of the following:
- Repeatedly walking over the same area when the active layer of soil is thawed.
- Driving vehicles or heavy equipment on tundra when the active layer of soil is thawed.
- Repeatedly driving vehicles or heavy equipment over the same area at any time.
- Excavating (Tactic CR-13), trimming (Tactic CR-12) or trenching (Tactic CR-9).
- Using high-pressure or hot water to flood (Tactic CR-7) or flush (Tactic CR-8).
- Injuring the root mat while burning (Tactic CR-10) or scraping (Tactic CR-12), especially when the soil is very dry.
Vehicle and foot traffic over thawed tundra can destroy vegetation and permanently compress organic soils. These ruts or compressed areas may change site drainage patterns, causing drying of some areas and inundation of others. Damage to vegetation and compression or removal of organic soils may reduce their insulating effects on the tundra surface, which can cause underlying permafrost to thaw and the soil to subside (thermokarst). Thermokarst can change dry or moist tundra to wet or aquatic tundra by creating depressions that fill with water. Once the thermal regime and drainage of an area are disturbed, the changes may be essentially permanent.
Traffic on wet tundra during summer can result in a disturbance that is highly visible, because vegetation and soil are compressed and the tracks fill with water. However, the wetland sedges that dominate wet tundra vegetation often recover rapidly from mild to moderate disturbance. The main concern with summer travel on wet tundra is the relatively high potential for vehicles to become stuck, which may result in more substantial damage that requires treatment. Traffic on dry tundra may appear to cause less damage because there are fewer plants and no standing water, but the physical effects are likely to persist for longer than in wet tundra.
In order to minimize physical damage to tundra during spill cleanup:
- Limit foot and vehicle travel on tundra as much as possible.
- Avoid following the same path repeatedly (enter and exit the site from different paths, if possible).
- Use existing roads (gravel, peat, or snow) as much as possible.
- Use snow ramps to access tundra from gravel roads and pads.
- Use existing gravel and ice pads for staging where possible.
- Use plywood or interconnecting rig mats as boardwalks or working platforms for light equipment (Fig. 13).
- Use snowshoes when repeated trips on foot cannot be avoided.
- Limit use of invasive treatment tactics (e.g. trimming) as much as possible.
- Replace displaced tundra sod back into original divot, or transplant tundra sod (Tactic TR-10) to replace soil and vegetation that have been removed.
- Restore natural contours and drainage by filling excavations.
Considerations and Limitations
- Boardwalks should be light enough to be moved manually, so they can be easily moved around the site as needed (Fig. 14).
- If treatment tactics require heavy equipment, tundra travel permits, proper road construction, or use of rig mats may be required (Tactic P-5).