46 



BULLETIN 1017, TJ. S. DEPARTMENT OF AGRICULTURE. 



of precipitation and run-off are shown in Tables 6 and 4. During 

 the period 1882 to 1919, maximum monthly precipitation occurred 

 8 times in May, 13 times in June, 11 times in July, 5 times in Au- 

 gust, and once in September. Maximum precipitation for a single 

 month during the 38-year period occurred in June, 1915. June is 

 recorded also as the month having the highest mean monthly pre- 

 cipitation during the period. For this same period the maximum 

 monthly run-off occurred once in March, 24 times in April, 4 times 

 in May, 3 times in June, 4 times in July, once in August, and once 

 in October. Maximum run-off during a single month occurred in 



III 



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Mlttcfsll lllllltlllll lllllltlllll W^R 





MMlfSX^^ 



Fig. 18. — Monthly precipitation and run-off, Red River of the North watershed above 

 Grand Forks, N. Dak., for 1882, 1896, 1897, and 1916. 



April, 1897, while the month having the highest mean monthly run- 

 off for the period also is April. Thus the records show June to be 

 the month of greatest precipitation, and April the month of greatest 

 run- off. 



Various combinations of maximum monthly precipitation and run- 

 off as recorded for the watershed above Grand Forks for the period 

 1882 to 1919, are shown in figure 17. Quantities of a similar kind 

 for 1882, 1896, 1897, and 1916 are shown in figure 18. These dia- 

 grams indicate that during the period of April to November, inclu- 

 sive, excessive monthly precipitation tends to produce high run-off 

 during the next following month, and that the excessive precipita- 

 tion is not reflected to any marked extent in the run-off for the same 

 month in which such precipitation occurs. 



