36 BULLETIN 1017, U. S. DEPARTMENT OF AGEICULTUEE. 
SNOW. 
In the Red River 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 
CANADA 
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 River 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 
