16 BULLETIN 832, U. S. DEPAREFMENT OF AGRICULTURE. 
recently constructed channel and that the bottom slope and cross- 
sectional area are more uniform throughout the course than for Old 
Town Creek. 
TWENTY-MILE CREEK. 
The slope course on Twenty-Mile Creek was rather short, being 324 
feet in length, and was located below the highway bridge 1 mile east 
of Baldwyn, Miss. (see Pl. ITI, fig. 2; and figs. 1 C, and 2 @). The 
lower part of the channel was quite smooth and regular, but the upper 
part and edge of bank were irregular. The channel is eroding rapidly, 
and many stumps along the banks have been undermined and fallen 
into the channel. Table 1 shows the hydraulic elements and the 
values of n obtained for Twenty-Mile Creek. The value of n increases 
as the stage increases, due no doubt to the irregularities in the wetted 
perimeter for the higher stages. The soil in the channel is a waxy 
clay loam, and in some parts of the channel contains considerable 
sand. 
CHAWAPPAH CREEK. 
Slope measurements tor Chawappah Creek were made en a rather 
short course (320 feet long) between the highway and railroad bridge, 
one-half mile south of Shannon, Miss. The gauging section was located 
at the highway bridge. The view of Chawappah Creek for low water 
(Pl. IV, fig. 1), shows very well the condition of the channel. The 
soil varies from a sandy loam te a waxy clay, and the sides and bottom 
were quite hard. The channel is eroding very rapidly, which is 
partly the cause of the turbulent water surface and the resulting 
comparatively high values of n. The average value obtained for n 
was about 0.035 (see figs. 1 D, and 2 D). 
COONEWAH CREEK, 
Only one observation for slope was made on Coonewah Creek. 
The value computed for n was 0.0430. Plate IV, figure 2, shows the 
course on which the slope was measured and the condition of the chan- 
nel. The soil is quite similar to that found on Chawappah Creek, 
but erosion has not been as active as on the latter (see figs. 1 HF, and 
2 Ff). 
DISCUSSION OF LEE COUNTY EXPERIMENTS. 
Of the experiments made in Lee County, Miss., the results obtained 
from those on Old Town and Mud Creeks are the most reliable. It 
appears that for conditions of flow the value of n for channels similar 
to Mud Creek is 0.025, which means that the bottom and sides should 
be fairly regular and free from any form of obstruction to flow, and 
the slope and cross-sectional area practically uniform. These con- 
ditions generally obtain only in new ditches, and it would therefore 
not be wise to use a coefficient as low as 0.025 in the design of chan- 
nels, since the efficiency of a channel generally decreases with age, as 
