FLOW OF WATEE IN" DEEDGED DEAINAGE DITCHES. 43 



water subsided the sides of the channel were left coated with a thin 

 layer of mud. The values of n obtained (Table 4) are higher than 

 those obtained for Allen and Willow Creeks, which is attributed to the 

 fact that the sides of the channel are considerably more irregular, 

 as may be seen by comparing the views of the channels. Also, it is 

 believed that the reduction of friction, due to the coating of mud on 

 the sides of the channels, was much more effective on the rather flat 

 side slopes of Willow and Allen Creeks than on the steeper side slopes 

 of the Boyer River channel. It will be noted that, for the Boyer 

 River channel, the value of n increases as the stage decreases. This 

 is due, no doubt, to the fact that the lower part of the channel is more 

 irregular than the upper part. 



PIGEON CREEK. 



Gaugings of Pigeon Creek were made at the highway bridge about 

 one-half mile above the Chicago & North Western Railroad, near the 

 town of Crescent. A view of the course of slope measurements is 

 shown in Plate XIV, figure 1. This view was taken looking down- 

 stream from the gauging station. The upstream slope posts, which 

 were about 65 feet below the bridge, can be seen on the right-hand side 

 of the view. 



The upper portion of the sides of the channel stand at a slope of 

 about 1 to 1 (see figs. 7 D, and 8 D), There was very little vegeta- 

 tion in the channel when the gaugings and slope measurements were 

 made. The soil in the channel is a heavy dark loam, and the bottom 

 of the channel is generally covered with § to 1 foot of mud, The chan- 

 nel was dug in 1907, and has increased somewhat in depth since that 

 time but not much in width. The right bank of the channel is 

 rather smooth and regular, while the left bank is rough and irregular. 

 During flood stages the channel was coated with mud, as described for 

 the channels near Missouri Valley. 



In Table 4, measurements 11 and 12, are shown two values of n 

 obtained for high stages in the channel. These values are much larger 

 than those obtained for Willow and Allen Creeks, which is perhaps due 

 to the rougher condition and greater fall of the channel, both of which 

 conditions probably rendered less effective the mud coating in reduc- 

 ing friction. 



MONONA-HARRISON DITCH. 



A view of the slope course on the Monona-Harrison ditch, near 

 Onawa, is shown in Plate XIV, figure 2. This view was taken looking 

 upstream from the gauging station, which was located at the highway 

 bridge on the Turin-Onawa road. The length of the slope course 

 was 948 feet. Experiments were made during the years 1916 and 1917, 

 and not much difference was found in the size and condition of the 



