- FLOW OF WATER IN DREDGED DRAINAGE DITCHES, £7 
is shown by the experiments on Oid Town Creek. It is believed that 
if the ditches are kept in good order the value of n can be maintained 
at approximately 0.030 for this section of country. If this value of 
nis to be maintained systematic maintenance work from the time 
the ditch is first constructed is necessary. 
EXPERIMENTS IN BOLIVAR COUNTY, MISS. 
The experiments in Bolivar County, Miss., were made on the fol- 
lowing streams: Bogue Phalia, Bogue Hasty, Pecan Bayou, West 
Bogue Hasty, and East Bogue Hasty. 
BOGUE PHALIA. 
The conditions for the accurate discharge and slope measurements 
on this channel were ideal. A straight course of practically uniform 
cross section was selected for slope measurements, about half a mile 
above the Yazoo & Mississippi Valley Railroad bridge, 2 miles from 
Helm. The length of the course was 1,003 feet. The gauging station 
was located near the lower end of the course, and the velocity meas- 
urements were made from a movable car suspended from a steel cable 
which was stretched across the stream at right angles to the direction 
of flow and supported by upright poles on either bank (Plate I, fig. 2). 
The left side slope of Bogue Phalia, along the-course, was quite 
regular while the right side was subject to caving and was only fairly 
regular. The channel was very smooth for low stages and of uniform 
section for all stages (fig. 4 A). Very little vegetation of any sort 
was found in the channel (Plate V, fig. 1; and fig. 3 A). The soil in 
the lower part of the channel is sandy. The soil in the upper part is 
a clay loam of close texture and is quite susceptible to caving, 
particularly when wet. ? 
The slope was indeed an extremely variable quantity. No two 
measurements of slope were found to be the same, due to the back- 
water conditions. The greatest slope was found for the lowest stage, 
and the others varied according to the effect of backwater at the time 
that measurements were made. 
The principal hydraulic elements of the channel and the values of 
Cand 7 obtained therefrom are shown in Table 2. Little variation 
was found in the values of C, and the values of n were found to vary 
from 0.0223 for the lowest stage to 0.0313 for the next to the highest 
stage. As would be expected, the values of n were found to be low 
for the lower stages, where the channel was quite smooth and uniform 
in section, and higher for the higher stages, where a greater resistance 
was offered to flow, by the rougher and more irregular sides of the 
channel. On the whole, it can be said that this channel! was in excel- | 
lent shape, a fact which is substantiated by the comparatively low 
values of n obtained. 
146908°—20—Bull. 832 2 
