Volumes of gravel removed from each site ranged from approximately 

 8,000 m to 630,000 m , with the largest volumes removed from Dietrich 

 Ri ver-Upstream, Phelan Creek, Aufeis Creek, and Sagavan irk tok River. Refer 

 to Table 4. Scraping was the most common removal method used, but four sites 

 were operated as pits and another four sites were operated as combinations 

 of scrapes and pits. Nine of the sites were developed in connection with 

 construction of the Trans-Alaska Pipeline System. Most North Slope sites 

 were opened in connection with oil exploration and drilling activities, 

 wh i le al I Seward Peninsula and most Southern Interior sites were developed 

 in connection with local highway projects. More detailed information on site 

 use is presented in DESCRIPTION OF STUDY RIVERS. 



Permafrost conditions at most of the study sites are unknown. There 

 normal ly is a thaw bulb associated with rivers in permafrost areas. In 

 continuous permafrost, the thaw bulb may be a transitory feature present 

 only during summer flows. However, in discontinuous permafrost and for large 

 rivers in continuous permafrost, the thaw bulb persists year-round although 

 it may shrink considerably in winter. A 1969 study on the Sagavan i rk tok 

 River I I km south of Prudhoe Bay (Sherman 1973) showed that in summer the 



thaw bulb associated with the main channel was 12 m deep and had a cross- 



2 2 



sectional area of 762 m . In winter, this thaw bulb shrank to 167 m with a 



maximum 7 m depth. Depending especially on whether underflow occurs, thaw 



bulbs may or may not be present outside the main channel. 



A major gravel use in arctic and subarctic Alaska is directly related 

 to the need to provide a gravel overlay sufficient to carry traffic and to 

 prevent permafrost degradation (progressive thawing). The minimum overlay 

 thickness to prevent thawing can be calculated as a function of the local 

 thawing index. The thickness is 1.5 m at Prudhoe Bay and increases as one 

 moves southward (e.g., it is 2.1 m at Galbraith Lake and in Fairbanks it 

 would approach 6m). A 1.5 m gravel overlay has generally been used for 

 roads, drillpads, airstrips, and other permanent facilities at Prudhoe Bay. 

 However, it has been shown that a 60-cm thick gravel overlay with 5 to 10 cm 

 of polystyrene insulation is thermally equivalent to 1.5 to 2.1 m of gravel. 

 This represents a 60 percent reduction in gravel thickness and a 64 percent 



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