36 



BULLETIN 1017, U. S. DEPARTMENT OF AGRICULTURE. 



SNOW. 



In the Eed Eiver Valley snow has an important effect on run-off 

 during March and April. Snow accumulates in varying quantities 

 during parts or all of the months of November to March, inclusive. 

 The run-off resulting from this stored precipitation was studied for 

 the period for which data were available, 1893 to 1920, inclusive. 

 Weather Bureau records of snow and ice conditions, showing the 

 amount of stored snow remaining on the ground each week from 



SOUTH DAKOTA 



Fig. 13. — Maximnm 3-day storm rainfall on watershed of Red River of the North, 



July 20-22, 1909. 



December to March, inclusive, were -summarized and are shown in 

 figure 15. It was found that when a considerable portion of the 

 watershed was covered with snow to a depth exceeding 15 inches 

 during the winter, and when near March 1, 12 inches or more of 

 snow remained on the watershed, high stages would occur in the 

 principal streams. In 1893, 1897, 1904, 1907, 1916, and 1920, when 

 flood stages occurred, this relation was found to be true. The only 

 exception was 1917, when the Red Eiver did not quite reach flood 

 stage, although there was quite a heavy snow covering on the water- 

 shed (see fig. 15). On March 1, 1920, the snow was from 6 inches to 

 15 inches in depth (average about 10 inches) : this snow melted 

 rapidly during the first half of March and the run-off therefrom 



