8 BULLETIN 101*7, U. S. DEPARTMENT OF AGRICULTURE. 



ditions of flow are suited for this purpose there is no need for irri- 

 gation. 



Under the conditions existing in this valley the most important 

 function of the watercourses is the removal of excess water. This 

 constitutes a combined problem of drainage and flood control which 

 is of vital interest over practically the entire watershed. This 

 problem is discussed later in the report. 



The Red River and its tributaries are the source of the water 

 supply for nine cities and towns having a total population of about 

 69,000. The most important considerations in the use of streams 

 for municipal water supply are the quantity and quality of the water. 

 It is not sufficient that the total amount of water passing through 

 the stream channel during the year be great enough to supply de- 

 mands ; the flow must be so distributed, either naturally or by arti- 

 ficial means, that at no time will it fall below a minimum consistent 

 Avith safety. To insure a sufficient degree of dilution of impurities 

 and provide for future increased demands, this minimum flow should 

 always be many times greater than the rate at which the water is 

 withdrawn from the stream for use. In populated districts stream 

 water is seldom of such quality that it can safely be used for domestic 

 purposes without treatment. Where the streams furnish the water 

 supply the flow is abundant except at certain points on the Red Lake 

 River where the flow during exceedingly dry seasons becomes so 

 small as to occasion concern over the concentration of impurities. 

 The increase in minimum flow planned for this river as a part of the 

 Red Lake project would improve this condition. In some of the 

 smaller tributaries the dry-season flow is so slight that water supply 

 from this source is impracticable. In most cases the water taken 

 from the streams is passed through filters which remove the greater 

 part of the suspended impurities, and in the upper parts of the 

 streams such treatment is sufficient to render the water fit for use. 

 However, the water of this drainage basin is very " hard," owing 

 to salts leached from the ground, and can be much improved for 

 domestic use by softening through chemical treatment. In the lower 

 parts of the streams where the accumulation of impurities from 

 above is greater, chemical treatment also is necessary especially dur- 

 ing low-water periods, to assure absence of organisms dangerous to 

 health. Fargo and Grand Forks are now operating plants for such 

 treatment of the water, and it is probable that, as the cities along 

 the streams grow and become more numerous, chemical treatment 

 will be commonly resorted to. 



The streams in the Red River basin are more used as a means of 

 sewage disposal than for water supply. By dilution and by 

 the action of natural purifying agencies, obnoxious and dan- 

 gerous effects of this contaminating content are eliminated or 



