OVERFLOW OF RED RIVER OF THE NORTH. 55 



bed and into the main river. In many cases they parallel the river 

 for some distance before finding outlet. They have sinuous courses 

 and the channels are more or less obstructed by vegetation. Many 

 of them originally spread out as marshes over the flats along the 

 Red River and had no definite channels for some distance. Some of 

 these streams have been improved through the flat areas by artificial 

 channels which carry the water coming down from the higher parts 

 of the basin and also provide outlet for the drainage of the marsh 

 lands. The flow in the lower parts of most of these tributaries is 

 sluggish, and many are subject to overflows during heavy run-off. 

 Overflow near the mouth is caused in some cases by backwater from 

 the Red River. 



EFFICIENCY OF THE NATURAL DRAINAGE SYSTEM. 



The general condition of the natural streams of the watershed 

 results, during periods of heavy run-off, in constantly augmented 

 bodies of water coming down badly obstructed channels of small and 

 constantly diminishing slope, piling up as they progress, overflowing 

 stream banks, and finally all uniting in a common channel charac- 

 terized by the same conditions of slight fall, obstruction to flow, 

 and diminishing slope; all this resulting in the overflow of large 

 areas of flat land along the main stream. A study of the various 

 streams of the basin shows that, with the exception of those with 

 relatively small contributing areas, the channels are or can be made 

 sufficient to carry the run-off during the summer months without 

 overflow. In cases of intense local storms over limited areas, serious 

 damage has at times resulted from flooding during the summer, but 

 where the drainage area involved is greater than about 6,000 square 

 miles the extent of heavy precipitation and the concentration of the 

 run-off is not great enough to cause damaging overflow. It is the 

 spring run-off, resulting from melting snow and ice and the general 

 spring rains, that causes the floods which cover a large portion of 

 the valley. 



ARTIFICIAL CHANNELS. 



Artificial drainage channels serve the double purpose of facilitat- 

 ing the movement of the flood waters to the natural channels and of 

 providing outlet where natural drainage is lacking or inadequate. 

 In the former capacity they provide a means for the rapid escape 

 of the excess surface water during periods of snow melting and 

 heavy precipitation, removing it quickly to the natural channels. In 

 swamp regions they remove the permanent excess of water, making 

 possible the agricultural development of the land. They are, in 

 short, an elaboration of the natural drainage system of the watershed. 



