FLOW OF WATER IK" DFvEDGED DRAINAGE DITCHES. 3d 



ALLEX CREEK. 



Gaugings of Allen Creek were made from the first highway bridge 

 north of the Chicago & North Western Railroad about 1 mile west 

 of Missouri Valley. The upstream end of the course for slope meas- 

 urements, which was 794 feet in length, was about 130 feet down- 

 stream from the bridge. A view of the slope course is shown in 

 Plate XII, figure 2. It is seen from this view and from figure 7 A, 

 that the course is straight and that the side slopes of the channel are 

 very smooth and regular and stand at a slope of about lh to 1. No 

 appreciable amount of vegetation can be seen in the channel. This 

 stream was enlarged to its present size during the summer of 1916, 

 and the measurements for values of n were made about one year 

 later. The soil in the channel is a heavy dark loam. The bottom 

 of the channel is generally covered with soft mud to a depth of one- 

 half to 1 foot, and the side slopes, after high stages in the channel, 

 are left covered with a coat of slippery, slimy mud or silt. This coat 

 can be seen by an inspection of Plate XII, figure 2. Two values of 

 n were determined for practically bankful stages. These values are 

 0.0140 and 0.0142 (Table 4, measurements 1 and 2), which are ex- 

 ceedingly low for dredged drainage ditches and may be ascribed 

 in part to the excellent condition of the channel and the uniformity 

 of cross section (fig. 8 J.), but mostly to the actual lining of the entire 

 perimeter of the channel with a coating of slimy, slippery mud. 

 This coating of mud no doubt greatly decreased the friction between 

 the moving water and perimeter of the channel. 



WILLOW CREEK. 



Discharge measurements of the Willow Creek dredged channel 

 were made at the Chicago & North Western Railroad bridge near 

 Missouri Valley. The slope posts for the upper end of the slope 

 course were set about 155 feet below the bridge, the length of the 

 course being 1,004 feet. It can be seen from figures 7 B, and 8 B, 

 and Plate XIII, figure 1, that the slope course is straight and very 

 uniform in cross section. The left side slope is much more regular 

 and smooth than the right side slope and resembles the slopes of the 

 Allen Creek ditch in this respect. Some vegetation can be seen in 

 the channel, but it was not present when the gaugings and slope meas- 

 urements were made. This channel is comparatively new^ having 

 been enlarged to its present size during the summer of 1916, and these 

 measurements were made and views taken about one year later. The 

 soil in the channel is a heavy dark loam, similar to that found in the 

 Allen Creek channel. The bottom of the channel was covered with 

 from 1 to li feet of mud during these experiments, and the coating 

 of the perimeter of the channel with slimy mud during high stages 

 was practically the same as in Allen Creek. In general, the channel 



