CYPRESS CREEK DRAINAGE DISTRICT, ARKANSAS. 9 
began to back up the creek on March 28 the discharge was 2,730 
second-feet from a drainage area of 390 square miles, or 7 second- 
feet per square mile. Considering the heavy rains that followed, it 
is safe to say that a much greater discharge would have been obtained 
if a measurement could have been taken on April 4. 
A current-meter measurement was made of Black Pond Slough 
at the railroad bridge west of Halley on the evening of April 4, 1911. 
This measurement gave a discharge of 449 second-feet from a drain- 
age area of 23.5 square miles, or the rate of run-off was 19.1 cubic 
feet per second per square mile. 
In planning the improvements of the Bogue Phalia, in Bolivar 
County, Miss., the 24-hour run-off was one-half inch from a drainage 
area of 350 square miles. The results so far observed seem to justify 
the use of this coefficient. The conditions in the Bolivar County 
district are very similar to those in the Cypress Creek district. 
Other run-off data for the Mississippi Valley have been examined, 
including those obtained in Coahoma County, Miss., by C. W. Okey, 
and much that have been compiled by the Tallahatchie drainage 
district, Mississippi. 
DETERMINATION OF RUN-OFF COEFFICIENTS. 
Experience has shown that draining and clearing timbered land 
results in an increased rate of run-off, and so far as the district in 
question is concerned, there is ample reason to believe that such 
will be the case. The water that under present conditions can reach 
the main outlets only by circuitous routes will, after the drainage 
system is installed, have direct access to the drainage outlets through 
the numerous submains and laterals penetrating the interior. Such 
storage capacity as now exists will be greatly reduced. The sub- 
stitution of deep, well-aligned ditches for the existing tortuous, 
debris-filled natural channels will facilitate the movement of the 
water from the entire drained area; in other words, will cause a 
quicker and more intense run-off than obtains under present con- 
ditions. In view of the effects that draining the land will have, it 
would be unsafe to base the selection of the run-off coefficients 
entirely upon the results of any gaugings made under present condi- 
tions, although these are useful in serving as checks upon such con- 
clusions as may be reached. 
In deciding upon the run-off coefficients to be used for the Cypress 
Creek drainage district the following method was pursued: Atrial 
coefficient was selected for a small area, one for a medium area, and 
one for a large area, and an algebraic expression was then sought 
whose curve would approximately fit these platted coefficients. 
The run-offs for intermediate areas were then calculated and plotted 
and the curve thus obtained was compared with all the data derived 
82085°— Bull. 198—15 2 
