4 J. Brown et al. 



The relief of the Coastal Plain reflects the lakes, river terraces, ice- 

 wedge polygons and occasional pingos. Along the 1800-km coastline 

 relief averages 2 to 5 m, with some bluffs and cliffs exceeding 20 m. The 

 75-m topographic contour is taken as the boundary between the northern 

 Foothills and the plain. Because of the very low relief and the presence of 

 permafrost, drainage is poor and stream channels meander widely. Only 

 one major river, the Inaru, lies completely within the plain. It flows only 

 for a few weeks during spring melt. Other rivers that flow north through 

 the plain originate in the foothills or mountains of the Brooks Range and 

 generally flow throughout the summer. The largest river to traverse the 

 Coastal Plain, the Colville River, drains 60,000 km^ of the Foothills and 

 western Coastal Plain (Walker 1973). It rises in the western Brooks 

 Range and flows eastward through the Foothills, then northward across 

 the Coastal Plain to the Beaufort Sea . The Colville intercepts drainage 

 from the Brooks Range, and thus limits the distribution of calcareous al- 

 luvium derived from the mountains to the area south and east of the river 

 (Figure I-I). 



The coastal climate is one of long, dry, cold winters and short, 

 moist, cool summers (Table I-I). At Barrow, the northernmost point in 

 Alaska, the sun is above the horizon continuously from 10 May to 2 

 August, and below the horizon from 18 November to 24 January. Air 

 temperature remains below freezing for nine months of the year and can 

 fall below freezing during any of the three summer months. The micro- 

 climate is strongly influenced by the presence of an insulating snow cover 

 20 to 40 cm thick in winter, and by the underlying permafrost. A gradual 

 warming trend begins in April and there is a definite transition toward 

 summer conditions during May. Snowmelt, however, does not normally 

 begin until early June. Thirty-seven percent of the annual precipitation 

 falls as rain during the summer. The windspeed varies little during the 

 year, averaging 5.3 m s"', with the fall months being the windiest. Fog 

 and clouds persist through the summer; the average humidity is consis- 

 tently above 80<^o from June through September. 



Based on the 30-year normal for Barrow, the period during which 

 daily average temperatures remain above 0°C lasts 91 days (13 June to 12 

 September). By our definition the thaw season begins when there are at 

 least three successive days with average temperatures above freezing and 

 ends when there are at least three successive days with temperatures 

 below freezing. This period is extremely variable and can begin as early 

 as 1 June and end as late as the end of September. An average of 251 

 degree-days above 0°C accumulates (30-year normal) and the wet tundra 

 soils thaw to approximately 30 to 40 cm. The initiation of the plant grow- 

 ing season coincides with the occurrence of snow-free conditions for a 

 particular tundra site. This date is also variable based on both season and 

 microtopography; however, it generally follows within several days of 



