OVERFLOW OF RED RIVER OF THE NORTH. 63 



flow is placed at the extreme east end. Both of these structures are 

 to be of reinforced concrete. For the location, elevation, and dimen- 

 sions of the dam see figure 3, sheet 2, and figure 4. A levee at the 

 south end of the lake, near Browns Valley, will be necessary to pre- 

 vent overflow into Bigstone Lake. A channel extending about 2 miles 

 back into the reservoir is planned to facilitate flow to the sluiceway. 

 The embankment of the railroad spur from Browns Valley to the 

 grain elevator at the south end of Lake Traverse must be raised to 

 avoid interruption of traffic by water in the reservoir. (See fig. 

 3, sheet 1.) On account of the navigation on Lake Traverse it is not 

 permissible to lower the water surface of the lake artificially below 

 elevation 972, the present low-water stage. As the breaking of the 

 reservoir when full would cause a great flood and much damage to 

 property and crops, it has been made of such dimension as will give a 

 large factor of safety, and it will store the run-off from a storm much 

 larger than any on the Red River of which we have a record. 



RUN-OFF TO BE CONTROLLED. 



Fairly complete precipitation records from about 1893 to date are 

 available, as are also data (April, 1917, to date) from which the dis- 

 charge of the Mustinka River into Lake Traverse can be computed, 

 and for the discharge of the Bois de Sioux for 1919 and 1920. In 

 addition there are some data relative to flood heights and a few 

 measurements of run-off made in the watershed. Also, there is avail- 

 able considerable information in regard to run-off from other drain- 

 age areas in the watershed of the Red River. The records of dis- 

 charge are shown in Table 3. In view of the paucity of actual flood 

 discharge measurements it was necessary, in order to decide upon 

 the probable run-off from the watershed under consideration, to es- 

 tablish some relation between precipitation and run-off. 



In studying the available records of run-off, as shown in Table 3, 

 it was found that by far the greatest run-off per square mile that 

 has ever been recorded in any watershed tributary to the Red River 

 occurred in the Wild Rice watershed in Minnesota as a result of 

 the storm of July 21-23, 1909. (See Table 9.) Computations of 

 monthly and annual run-off for the period July, 1909, to December, 

 1917, also show that the maximum monthly and half-yearly run-off 

 measured during that period occurred on the Wild Rice River during 

 1909. 



As the run-off from January to June, 1909, was not measured and 

 a maximum year could not be estimated therefrom, the records from 

 January to June, 1916 (showing maximum half-yearly run-off since 

 1909), and from July to December, 1909, were combined as though 

 they had occurred in one year. The period January to June, 1916, 



