BULLETIN 832, U. S. DEPARTMENT OF AGRICULTURE. 

 [Cross-sectional area=315.6 square feet. Hydraulic radius=5.45 feet. Slope= 0.0003.] 



Channel. 





C 



Mean 



Dis- 





velocity. 



charge. 







Ft. 









per sec. 



Sec. feet. 



0. 0367 



56.2 



2.27 



715-1 



.0619 



34.8 



1.40 



443. 5 



.1460 



15.1 



0.61 



192.7 



Relative 



dis- 

 charges. 



Dredged 



Old straight 

 Old crooked 



Per cent. 

 100.0 

 62.1 

 27.0 



Results of the above computations show that for similar cross 

 sections and slope the dredged, old straight, and old crooked channels 

 would carry 715.1, 443.5, and 192.7 second-feet, respectively, the 

 capacity of the old straight channel being only 62.1 per cent of that 

 of the dredged, and of the old crooked channel only 27 per cent of the 

 dredged. The difference in the capacities of the old straight channel 

 and old crooked channel is not due entirely to the curves in the latter, 

 since the accumulation of drift, trees, and logs was greater in the 

 crooked channel. However, the difference in the condition of the 

 two channels may be directly attributed to the presence of the 

 curves, since there is a greater tendency for drift and other obstruc- 

 tions to accumulate in a crooked than in a straight course of channel. 



DISCUSSION OF WESTERN TENNESSEE EXPERIMENTS. 



The experiments in western Tennessee cover a greater variety of 

 conditions in channels than do any of the other six sets, the values 

 of n obtained ranging from 0.024 for the dredged channels near 

 Roberts and Trenton to 0.162 for the old crooked river channel near 

 Jackson. The results, however, do not justify the use of a coefficient 

 as low as the first named above in the design of dredged channels, 

 since it is not the rule that a dredged channel maintains its original 

 efficiency. It is not believed that a value of n less than 0.030 should 

 be used for this section of the country, and it will be noted that this 

 statement is in agreement with the conclusions deduced for the two 

 sets of experiments made in Mississippi. Where it is desired to com- 

 pute the capacity of an existing channel, the proper value of n can 

 be selected by a comparison of the conditions in the channel with 

 the conditions described for the various channels for which n has 

 been determined in these experiments. 



EXPERIMENTS IN WESTERN IOWA. 



Experiments in western Iowa were conducted on the following 

 streams: Allen Creek, Willow Creek, Pigeon Creek, Boyer River, 

 the Monona-Harrison Ditch, and Little Sioux River. 



