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 rinding 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 clown 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. 
