FLOW OF WATER IN DREDGED DRAINAGE DITCHES. - 15 
of flow changes. For low water conditions the loss in shock and eddies 
is quite appreciable, and as the values of n were obtained by directly 
measuring this total loss of head throughout the course these values 
would be necessarily large. The table shows that for such conditions 
the value of n decreases as the depth increases. This would be ex- 
pected, for as the depth increases the second factor mentioned above 
becomes comparatively smaller, and the total loss of head thus be- 
comes to a greater extent due to roughness of wetted perimeter and 
to a less extent due to the influence of eddies and shock. 
in measurement No. 9, Table 1, forn=0.0475 the discharge is 60 
second-feet; that for n=0.030,' and the same hydraulic elements, is 
96 — 60 
60 
of the lower part of the channel for low water could be increased 60 
per cent by eliminating irregularities in the bottom slope and abrupt 
changes in cross section. As will be seen later, the bottom slope and 
cross section of Mud Creek are practically free from irregularities, 
and the values of n do not vary much from low to high-water flow. 
96 second-feet. x 100=60 per cent. That is, the capacity 
MUD CREEK. 
Measurements were made on this channel during the early part oi 
the year 1914. For the slope measurements a straight course 1,194 
feet long was selected above the highway bridge about 1 mile east of 
Tupelo. A suspension footbridge was constructed at a site where 
conditions were ideal for makimg accurate current meter measure- 
ments. 
A good idea of the condition and regularity of the channel can be 
obtained from Plate III, figure 1. Although in the same valley, the 
soil is decidedly different from that found in Old Town Creek. This 
part of the bottom land is made up of sediment carried from the east- 
ern part of the Mud Creek watershed, where the soil contains consider- 
able sand. The soil in the channel is a sandy, waxlike clay that 
erodes very easily. This was a comparatively new channel at the 
time of these experiments, the ditch having been finished in January, 
1913; and, although it had eroded to some extent, it had retained its 
original uniform slope and comparatively uniform cross-sectional 
area (see figs. 1 B, and 2 B). 
In Table 1, measurements 22 to 34, are shown the various hydraulic 
elements of Mud Creek as computed from field measurements, and 
the values of n obtained. That for all stages of Mud Creek is about 
0.025, while that obtained for the higher stages in Old Town Creek, 
after clearing, is about 0.030. The lower value of n as obtained for 
Mud Creek can readily be ascribed to the facts that this is a more 
1 See measurements 22-26, Table 1. 
