12 BULLETIN -832, U. S. DEPARTMENT. OF AGRICULTURE. 
OLD TOWN CREEK. 
Measurements were made on this channel early in 1913 and in 1914. 
A straight course of 1,224 feet below the steel highway bridge, one- 
half mile east of Tupelo, Miss., was selected for making the measure- 
ments. The discharge measurements for 1913 were made from the 
highway bridge and those for 1914 from a suspension footbridge 
constructed near the upper end of the course. The latter gaging 
section was much more desirable for accurate measurements than the 
former one. ; 
An experiment for determining the effect upon the flow in the 
channel, due to the clearing of brush and other resistances to flow, 
was conducted on Old Town Creek. No clearing was done for the 
measurements during 1913. One side slope of the channel and part 
of the bottom were practically covered with small saplings, brush, 
and cane, and were quite irregular. The other side slope was com- 
paratively smooth and uniform. For the measurements during 1914 
all brush, logs, and other obstructions were cleared from the course 
of the channel and for 500 feet above the upper end and for the same 
distance below the lower end of the slope course, so that a comparison 
could be made as to the relative values of n before and after clearing. 
The slope of the left bank was quite regular while that of the righ 
bank was extremely irregular, a condition due to the growth of brush 
causing the bank to erode uneyenly. The soil in the bottom and sides 
of the ditch was quite hard. The views shown in Plate II give a good 
idea of the conditions existing in the channel before and after clearing. 
(See also fig. i A, for average cross section of the channel.) 
In Table 1, measurements 1 to 21, are given the valnes obtained for 
n, together with the various observed hydraulic elements. It is 
obvious, from the values of 7 obtained before and after clearing, that 
the efficiency of a channel is greatly decreased by permitting the 
growth of vegetation in it. 
During low water the uniform fall of the surface of the water 
was interrupted by irregularities in the bottom and sides of the chan- 
nel. For such conditions the hydraulic grade throughout the section 
consisted of a series of comparatively steep slopes followed by flatter 
ones, due to the depth of water bemg so small that the irregularities 
in the channel gave rise to quite appreciable variations in area of 
cross section from point to point, thus causing variations in velocity 
and in the hydraulic grade (see fig. 2A). Asa result the values of n 
obtained for low water conditions are high. The total loss of head 
throughout the course under such conditions is the sum of the loss 
due to the roughness of the wetted perimeter and the quite appreciable 
losses in shock and eddies that occur where the hydraulic gradient 
changes from a steeper to a flatter slope and where the cross section 
