46 
BULLETIN 1017, U. S. DEPARTMENT OE AGRICULTE/RE. 
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 
™r*mm%faxnrxA \ aaB ffl%m B r& aa * a A w^mm mnr**** i — jmrn-m^M 
mmmmk mwrnmi mmmmi mmnnm 
Fig. 18. — Monthly precipitation and run-off, Red River of the North watershed above 
Grand Forks, X. 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. 
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