FLOW OF WATER IN DREDGED DRAINAGE DITCHES, 39 
ALLEN 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 1} 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 
nm 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 A), 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 14 feet of mud during these experiments, and the coating 
of the perimeter of the channel with simy mud during high stages 
was practically the same as in Allen Creek. In general, the channel 
