48 
BULLETIN 1017, U. S. DEPARTMENT OF AGRICULTURE. 
While figure 19 does not alone form sufficient basis fcfr estimating 
maximum future run-off. yet the relations existing between volumes 
and intensities of precipitation and run-off. time periods, and areas 
are of importance in estimating future run-off which may result j 
from summer storms. 
ESTIMATES OF PROBABLE RUN-OFF. 
In Table 5 are shown the estimated rates of run-off for various 
subdivisions of the Red River watershed. The basis for these esti- !: 
mates is all available run-off records for annual, monthly, and daily I J 
periods, and for flood periods during spring and summer seasons, • j 
as well as data on precipitation and the results of a study of the 1 
various other conditions that affect run-off. As may be noted from 
Table 5, the rates of run-off shown are not expected to occur in such 
relation with respect to time that the excessive flow from all sub- j 
divisions will concentrate in the outlets. 
Frequently, in connection with engineering reports on undertak- 
ings similar to the Red River project, certain formulae or equations I 
are developed or equations previously evolved are adopted for use (j 
in estimating run-off. In the present instance, however, each water- 
shed is a problem of itself and any attempt to calculate run-off for vi 
the larger watersheds (say those of more than 200 square miles) by 
formulae is likely to give results which would be quite unreliable i j 
owing to the wide variation of the influencing conditions and to the > I 
difficulty of assigning definite values to them. Accordingly no 
formula, equation, or curve has been developed and none is to be 
recommended. • 
KTJN-OFF FKOM SMALL WATERSHEDS. 
For small watersheds, containing less than about 200 square miles, 
the size of watershed drained is usually the dominating feature in 
determining the rate of run-off. For such areas a run-off formula 
in which the area of watershed is the principal factor may give satis- 
factory results if care and judgment are used in applying the 
formula. 
Table 12. — Estimated run-off. per square mile, from small watersheds. 
Area (square miles). 
Minne- 
sota. 1 
Cu.ft. 
per sec. 
12.0 
North - • 
Dakota. 2 
Cu.ft. 
per sec. 
13.4 
11.8 
11.2 
10.0 
8.4 
7.7 
Area ' square miles 
2',.. 
30.. 
49.. 
50.. 
75.. 
100. 
1.50. 
200. 
Minne- 
North 
sota. 1 
Dakota 2 
Cu.ft. 
Cu.ft. 
per sec. 
per sec. 
8.7 
6.7 
8.5 
6.6 
8.3 
6.4 
8.1 
6.2 
7.8 
5.9 
7.7 
5.8 
7.3 
5.3 
7.0 
5.1 
By J. T. Fanning, 1886. 
2 Bv J. T. Stewart, 1907. 
-A 
