OVERFLOW OF RED RIVER OF THE NORTH. 69 



for an area as large as that draining to Lake Traverse. A discharge 

 from the reservoir of 4,000 second-feet would flood the lands below 

 the dam during the time that rate was maintained, and for a short 

 time afterwards. It appears, however, that ample capacity with a 

 safety factor for the most extreme conditions that will occur will be 

 provided by the proposed works, and that the necessity for discharge. 

 at the rate of 4,000 second-feet would occur only at long intervals, 

 if ever. The factor of safety in the case of the reservoir is some- 

 what higher than would be considered necessary in designing chan- 

 nels for the uncontrolled disposal of run-off. This is. considered ad- 

 visable in view of the cost of the reservoir, and the extent of damage 

 to the controlling works which would follow failure of the dam, as 

 well as the disastrous results in the valley below. 



THE OUTLET CHANNEL. 



The location and courses of the proposed outlet channel are shown 

 in figure 3, sheets 2, 3, and 4. Typical cross sections are shown in fig- 

 ure 4. As planned, the channel would follow the general course of 

 the Bois de Sioux River with such cut-offs as are considered advan- 

 tageous. It is possible to obtain a uniform slope of 0.0001 (about 

 one-half foot per mile) for the entire length of 22| miles. For 

 the first 13 miles the proposed channel has a bottom width of 40 

 feet, widening out to 52 feet just above the entrance of lateral 1 

 of the secondary system (see fig. 3, sheets 2 and 3) and continuing 

 thus for 4^ miles to the mouth of the Rabbit River where the bottom 

 width again increases and continues at 80 feet to the end of the ex- 

 cavated channel, about 5| miles south of Wahpeton. Side slopes of 

 1.1 are planned throughout. To obtain the necessary capacity in 

 the Bois de Sioux channel between the end of the excavated channel 

 and Wahpeton, it would be necessary to clear out the brush, trees, 

 and debris, but no excavation is contemplated here. The sluiceway 

 in the dam would discharge directly into the upper end of the outlet 

 channel, and the spillway overflow would reach it just below through 

 a short channel (see fig. 3, sheet 2). 



The normal capacity of the upper 13 miles of the channel is 1,000 

 second-feet, increasing to 1,300 second-feet and 2,000 second-feet at 

 the outlets of lateral 1 and Rabbit River, respectively, to provide for 

 the additional flow entering at these points. A 10-foot depth of flow 

 is sufficient to give these capacities, although a somewhat greater 

 depth is available at all points below the outlet of lateral 1. To pro- 

 vide for extreme conditions it is planned to make the spoil banks 

 on both sides continuous as far down as the outlet of lateral 1. 

 This will permit a flow of 2,000 second-feet, which is 1,000 second- 

 feet in excess of the normal capacity, without overflowing the ad- 

 joining land. The increased flow can be taken care of below this 



