OVERFLOW OF RED RIVER OF THE NORTH. 
45 
lent to the percentages shown in the table will occur during any 
year when annual precipitation is maximum in depth. 
Table 11. — Probable maximum annual run-off. 
Streams. 
Station. 
Drainage 
area. 
Ratio of 
annual 
run-off to 
annual pre- 
cipitation. 
Grand Forks, N. Dak 
Sq. mi. 
25, 755 
6, 435 
5,320 
1,080 
Per cent. 
15 
Do 
Fargo, N. Dak 
15 
25 
25 
TC4KH- 
IIIMItttSII 
Fig. 17.— Precipitation and run-off. Red River of the North watershed above Grand Forks, 
N. Dak., for selected months, 1882-1919. 1, Maximum monthly precipitation ; 2, run- 
off during months of maximum precipitation ; 3, monthly run-off immediately following 
maximum monthly precipitation ; 4, precipitation during months of maximum run-off ; 
5, maximum monthly run-off ; 6, monthly precipitation immediately preceding maximum 
monthly run-off. 
Investigation shows conclusively that run-off can not be determined, 
by considering it merely as a fixed percentage of precipitation. The 
part of precipitation that supplies demands of evaporation and plant 
transpiration is much greater and is more nearly uniform in quan- 
tity from year to year than is the part that goes into run-off. For 
the watershed above Grand Forks, comparisons of annual run-off and 
annual precipitation are shown in figure 16. Monthly distribution 
