62 BULLETIN 1017, TJ. S. DEPARTMENT OF AGRICULTURE. 
The information collected shows very clearly that the highest 
floods are those caused by melting snow, combined in some instances 
with rains at a time of the year when the ground is more or less im- 
pervious to water. However, the floods that have caused the greatest 
loss to crops have been those caused by heavy rains over the watershed 
during the period from May to August. The natural drainage is not 
capable of removing the run-off from heavy storms, such as occurred 
in 1916. in time to prevent flooding and serious damage to crops. In 
many instances where an attempt has been made to relieve this condi- 
tion by constructing ditches, it has not been possible to secure a safe 
factory outlet or the drains have been dug too shallow and too small. 
THE PKOBLEM. 
- In order to relieve the conditions just described, it is necessary 
either to provide channels of sufficient capacity to remove the run-off I 
from storms and spring thaws without flooding or so to control this 
run-off that the drainage channels shall not be overtaxed. A combi- 
nation of the two methods is recommended as most advantageous. A 
number of different plans for accomplishing these results were given 
careful study. Xo discussion will be given of the several plans con- 
sidered but not adopted. 
In reaching conclusions as to the conditions which must be met* 
in planning the improvements extensive and detailed studies were 
made of all available precipitation and run-Off records. These 
studies and the methods used in estimating requirements have been 
discussed, and only those phases that apply to this project in par- 
ticular will be taken up here. 
In planning for the drainage of this watershed provision has been 
made only for outlet drainage. Only those works have been in- 
cluded that will require joint action of the three States interested. 
Some suggestions are made as to lateral drainage, but it is believed 
that these local drains can be constructed most economically under 
the drainage laws of the State in which the drains are located. 
THE DETENTION RESERVOIR. 
The reservoir, by means of which it is proposed to control the run- 
off from the Lake Traverse watershed, would include that part of 
the present bed of the lake between Browns Valley. Minn., and the 
north line of sections 2± and '33. T. 128 N. Along this line, which 
is about 4 miles south of White Eock. S. Dak. (see PL V. fig. 
2), it is planned to build the earth dam extending to high ground 
on both sides. The proposed sluiceway for controlling the outflow 
is located at the intersection of the dam with the Boise de Sioux chan- 
nel, and the spillwav for protecting the dam from damage bv over- 
