64 



BULLETIN 1017, U. S. DEPARTMENT 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 Kiver in 

 Minnesota. A comparison of figures 6 and 7 shows that the com- 

 bined precipitation is heavier than that which occurred on the Wild 

 Rice watershed in 1896, the year of maximum recorded annual pre- 

 cipitation over the Red River 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 979. 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 Rice 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 Rice 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 Rice. Accordingly, 

 the run-off from the Wild Rice 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. 





0.13 

 .13 



0.06 

 19 



1.24 

 1.43 



2.83 



4.2G 



2.47 

 6.73 



3.10 

 9.83 



7. S3 

 17.66 



3.76 

 21.42 



0. ss 



0.28 



0.51 

 23.09 



0.34 

 2. 343 



23.43 



Accumulated 



22. 30 



22. 5S 





