OVERFLOW OF RED RIVER OF THE NORTH. 53 



tance back from the banks. The fall along its course is for the most 

 part slight and somewhat variable. Along the Bois de Sioux the 

 fall is about 0.3 foot per mile ; from Breckenridge to Fargo, about 1 

 foot per mile ; and from Fargo to the Canadian line from 0.6 to 0.3 

 foot per mile. (See fig. 2.) 



The channel of the upper Bois de Sioux is small and poorly de- 

 fined (see fig. 4 and Plate IV, fig. 1), but in the vicinity of Brecken- 

 ridge the banks are between 20 and 25 feet high, and from 100 to 200 

 feet apart. At this point there is a further increase in size due to 

 the entrance of the Otter Tail, and from Breckenridge on for the 

 greater part of its length the stream has an inner or low-water 

 channel with banks of varying height, with one or more terraces on 

 each side which bring the outer banks up to or slightly above the 

 level of the adjacent land. The outer banks, in places on the lower 

 part of the river, are from 1,000 to 1,200 feet apart. 



The course is extremely crooked for most of its length, with many 

 loops, bends, and side channels. The channel often doubles back 

 upon its course and flows a considerable distance without gain in the 

 general direction of flow. Over the greater part of its length the 

 channel — especially the outer flood channel — is badly obstructed by 

 trees and brush (see PI. IV, fig. 2) and many buildings, fences, and 

 other structures are situated within the outside banks. Many of the 

 county wagon bridges have been built on the inner banks, spanning 

 only the low- water channel (see PL IV, fig. 3) ; at flood stages these 

 are either washed out or completely covered, thus forming addi- 

 tional obstruction to flow. 



Owing to the slight fall in the stream bed and the fact that the 

 slope decreases downstream as more water is added, the velocities of 

 flow are small and channel erosion is comparatively slight. The 

 stream under these conditions has not a channel of sufficient capacity 

 at all points to carry the volumes of water present at high stages, and 

 the situation is rendered the more acute by the obstructed state of 

 the channel. As a result, heavy run-off from the watershed causes 

 the stream entirely to fill the channel and spread widely over the 

 contiguous country. 



The upper part of the Bois de Sioux has practically no channel 

 (PI. IV, fig. 1) and at times of high water the adjacent land to the 

 west becomes a part of Lake Traverse. The land to the east rises 

 sharply a short distance from the stream. Farther down, the chan- 

 nel gradually develops until at a point about 10 miles upstream 

 from Breckenridge it attains a capacity of 2,000 second-feet (see fig. 

 2 and fig. 4) . At Breckenridge there is a sharp increase in slope and 

 size of channel which gives a capacity of about 4,000 second-feet 

 within the inner banks and about 8,500 second-feet for the entire 

 channel. From Breckenridge to the international boundarv there is 



