OVERFLOW OF RED RIVER OF THE NORTH. 65 



This run-off represents conditions that would obtain if, after a wet 

 spring, a storm such as occurred in 1909 should cover the Lake 

 Traverse watershed. 



The relation between the precipitation and run-off for the storm of 

 July, 1919, was investigated in the same manner. It was found that 

 approximately the same percentage of run-off occurred from this 

 storm as from the storm of 1909 on the Wild Rice watershed ; but as 

 would be expected, on account of the greater storm area and less 

 intensive precipitation, the run-off extended over a longer period of 

 time. Plans were then worked out to control a run-off from the 

 Lake Traverse watershed of 23.43 billion cubic feet, which consti- 

 tutes the total run-off for the hypothetical maximum year. It is 

 equivalent to 25 per cent of the maximum annual precipitation 

 recorded on the watershed. 



OPERATION OF THE EESEEVOIE. 



The reservoir is designed so to control the run-off from the tribu- 

 tary watershed that there will be no outflow from it in the spring 

 before May 1 and, except under extraordinary conditions, the dis- 

 charge through the sluiceway into the outlet channel will at no time 

 exceed 1,000 second-feet. After May 1, such a flow can be accommo- 

 dated by the river below without difficulty, except possibly at times 

 of heavy storm run-off in the lower valley which may cause tem- 

 porary high river stages. To relieve the lower channel under such 

 conditions, the reservoir may be entirely closed for a period of at 

 least 15 days at any time necessary, thus eliminating for such a period 

 the flow from the Lake Traverse watershed. 



The flow through the sluiceway, as planned, can be maintained at 

 1,000 second- feet under varying head, by regulating the gate open- 

 ing, and at high reservoir stages over 2,000 second-feet can be dis- 

 charged when necessary. It is proposed to place the spillway crest 

 at elevation 983.0, which would give a storage capacity in the reser- 

 voir of 9.849 billion cubic feet when overflow begins. The spillway 

 is planned to discharge at a rate of 2,000 second- feet when the water 

 reaches elevation 985.0, which is 3 feet below the top of the dam. 

 With the water at this elevation the reservoir would hold 12.035 

 billion cubic feet and the spillway alone would be discharging at a 

 rate almost as great as the maximum rate of inflow which has been 

 recorded. Table 15 gives the storage capacities of the reservoir at 

 the different water surface elevations. 

 70352°— 22 5 





