Physics 67 



Over the entire year, about 37% of the precipitation runs off the pond 

 site drainage basin. This is much lower than other reported values for 

 permafrost areas. For small watersheds at Barrow, Brown et al. (1968) 

 assumed that all the winter snowfall runs off as well as 5% of the summer 

 rainfall to give a total of 52% for the year. Dingman (1973) summarized 

 arctic data and reported that in tundra areas in the USSR the runoff 

 ranged from 70 to 76% of the total precipitation. In the Brooks Range 

 where the drainage basin was steep and rocky, Hobbie (1962, 1973) found 

 that 85% of the total precipitation ran off over the entire year, a value 

 similar to that found by Kuzin (1960, quoted in Sater 1969) for Novaya 

 Zemlya. For a study of nutrient budgets of a high arctic, nearly 

 vegetationless drainage basin (Char Lake), Schindler et al. (1979) and de 

 March (1975) assumed that all snow and rainfall ran off. 



The percentage runoff from the Barrow ponds is low because of the 

 high evaporation and the very low precipitation. Most of the surface of the 

 watershed is standing water for some or all of the summer, so evaporation 

 and transpiration rates are always the highest possible. This loss lowers the 

 water level so that any summer precipitation fills up the ponds rather than 

 running off. If the total precipitation were increased, then almost all of this 

 increase might well run off and in this way increase the percentage. 

 Ultimately, the low runoff is caused by the flat ground, the many small 

 catchment basins formed by polygonal ground, and the low amounts of 

 precipitation. 



Evaporation and Pond Levels 



Evaporation was measured daily in the summers of 1971, 1972, and 

 1973 in a standard 1.21-m-diameter pan supported above the tundra 

 surface by a 5-cm-high wooden platform. It is well known that this method 

 overestimates the true evaporation from a free water surface by as much as 

 140 to 150% in dry regions (Harding 1942) but no correction values are 

 available for cold climates. Actually, the depth of the evaporation pan, 25 

 cm, was similar to the pond depths and the water temperatures were 

 virtually the same as in the pond. Therefore, we assume that the pan does 

 give an estimate of pond evaporation rates (Table 3-9). Other workers at 

 Barrow have found that evaporation from a pan was much greater (250%) 

 than the evapotranspiration from the surface of the tundra (Brown et al. 

 1968). 



Pond water levels were read daily in 1972 and weekly in 1970, 1971, 

 and 1973 from staff gauges anchored in the permafrost. The pattern of 

 water level changes (Figure 3-8) is similar in all the measured ponds for a 

 given year but there are year-to-year changes caused by the interactions of 

 precipitation and evaporation. Thus, the ponds begin to decrease in depth 

 in mid-June. The decrease was continuous throughout the summer in the 



