OVERFLOW OF RED RIVER OF THE NORTH. 
47 
. KUN-OFF DUE TO STOKM PRECIPITATION. 
Only casual examination of the data is required to make it appar- 
ent that storm precipitation during summer months often has marked 
effect on run-off in the Red River watershed. The effect is relatively 
greater and is more apparent on small watersheds of tributary 
streams than on large areas, because the most intense storm precipi- 
tation occurs on comparatively small areas. In figure 19 the pre- 
cipitation during four summer storm periods, each on a different 
5 10 15 20 
JULY 
Fig. 19. — Accumulated storm rainfall and run-off. 
watershed, is indicated in comparison with run-off which followed 
the storms. 
On watersheds of 10.000 square miles or less, storm precipitation 
sometimes causes maximum run-off; but on the larger watersheds, 
such as that above Grand Forks, spring run-off due to melting snow is 
greater. Accordingly', figure 19 as well as other data on storm pre- 
cipitation and summer run-off have been used largely in estimating 
probable maximum run-off for the smaller watersheds (see Table 5). 
