Introduction and Site Description 33 



IBP site 2 (Weller and Holmgren 1973). For example, on 7 July 1971 the 

 average wind speed (m sec"') at 0.25, 1, 2, 4, 8 and 16 m above the ground 

 was 2.5, 4.4, 4.5, 4.9, 5.2 and 5.5, respectively. 



Hydrology 



The vertical relief near Barrow is small; consequently the drainage is 

 poorly developed and small ponds and lakes are common. There are no 

 large rivers in this part of the coastal plain and the small streams are found 

 only where polygonal ground is absent. There is some overland drainage 

 from polygonal areas but only during the snowmelt or during rare periods 

 of heavy precipitation when the ponds become completely filled. As a 

 result, the two detailed studies that have been made concentrated on small 

 streams with well-developed channels. One of these streams is located on a 

 drained lake basin about 8 km northeast of Barrow (Brown et al. 1968), In 

 this basin the total elevation change is 0.3 m, the area 1 .57 km^ and open 

 water covers about 5% of the area. The other study was carried out by the 

 U.S. Geological Survey on two creeks near Barrow Village (Dingman et 

 al. in press). 



The snowpack reaches its maximum depth in February, March, and 

 April (Table 2-1). The actual depth of the snowpack in any one place 

 depends upon the microrelief, the wind during the snowstorms, and the 

 amount of time available for the snow to age and harden before the next 

 period of high winds. Not only is snow removed by the winds, but also 

 there is almost continual drifting so that huge drifts accumulate behind 

 every house and small drifts behind each ridge or hummock. Thus, even 

 the ponds, which usually have a complete snow cover, will have a variable 

 depth of snow cover depending upon their immediate surroundings. 



The snowfall and snowpack are highly variable from year to year 

 (Table 2-2) and averaged 91.7 and 41.3 cm, respectively, over the past 

 decade. 



In April and May there is an increase in insolation (Table 2-1 ) but the 

 continuous snow cover still has an albedo of 85% so little melting occurs 

 (Figure 2-4). Finally, in late May, the rising air temperatures and the 

 increasing solar radiation cause the first snowmelt. As the snowpack 

 begins to decrease and becomes saturated with water, the albedo falls and 

 more solar radiation is absorbed. Dingman et al. (in press) have 

 summarized the heat balance for the Barrow site for six periods in 1971 

 (Figure 2-5). The sudden change in the amount of energy going to melt the 

 snow is mostly caused by the sudden decrease in albedo from 85 to 48%. 



The snow has a mean extinction coefficient of 0.10 cm "' (Weller and 

 Holmgren 1974). Thus, little insolation penetrates the snow, and the pond 

 ice does not begin to melt until all the snow is gone. Most of the melting 

 occurs at the surface but some radiation also penetrates to the bottom 



