64 
BULLETTX 1017, IT. S. DEPARTAIEXT OF AGRICULTURE. 
was selected because the heaviest run-off for the first six months of 
a year was recorded during that year. The precipitation for these 
periods is shown in figure 7. It will, be noted that the heaviest pre- 
cipitation occurred over the eastern and southern parts of the water- 
shed, and that the precipitation diminished in intensity toward the 
northwest. It is thought that this combination, which includes the 
July, 1909, storm, will give a greater annual run-off than has ever 
actually occurred from the watershed of the Wild Eice Eiver in 
Minnesota. A comparison of figures 6 and 7 shows that the com- 
bined precipitation is heavier than that which occurred on the Wild 
Eice watershed in 1896 r the year of maximum recorded annual pre- 
cipitation over the Eed Eiver watershed. 
In computing quantities for which storage and outlet capacities 
must be provided in order to control the run-off, it is necessary to take 
into account the amount of evaporation from the water surface of the 
reservoir. Using figures shown in Table 10, these quantities were com- 
puted in billions of cubic feet for an area of 35 square miles, the area 
of the exposed water surface at elevation 9?9. Any rise above this 
elevation would cause only slight increase in the surface exposed. 
These quantities were deducted from the estimated inflow to the 
reservoir. 
A study of the relation of the run-off to rainfall in the watershed 
of the Wild Eice and the Mustinka. which latter is the principal trib- 
utary to Lake Traverse, indicated that the ratio was approximately 
the same for both watersheds. 
Available data indicated that the run-off per square mile from the 
Lake Traverse watershed might be expected to be as large as may 
occur from the Wild Eice watershed and that the monthly distribu- 
tions during the year would be nearly the same. The Lake Traverse 
watershed is 1.6 times as large as that of the Wild Eice. Accordingly, 
the run-off from the Wild Eice for the period January to June. 1916, 
and July to December, 1909, was increased by 60 per cent : and to 
make allowance for the earlier spring in the Lake Traverse water- 
shed, one billion cubic feet was transferred from April to March. 
The monthly evaporation from Lake Traverse was then deducted 
and the remainder was taken as the maximum amount of water for 
which provision must be made. Monthly and accumulated quanti- 
ties thus estimated are as follows, stated in units of billions of cubic 
feet. 
Jan. 
Feb. 
Mar. 
Apr. 
May. 
June. July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
An- 
nual. 
Monthly 
Accumulated 
... 0.13 
... .13 
0.06 
19 
1.24 
1.43 
2. S3 
4.26 
2.47 
6.73 
3. 10 7. S3 3. 76 
9. 83 17. 66 21. 42 
0.88 
22.30 
0.2S 
22. 58 
0. 51 
23. 09 
0.34 
2. 343 
23.43 
