CYPRESS CEEEK 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 di^ainage 

 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 

 tlie 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 arc useful in serving as checks upon such con- 

 'lusions as may be reached. 



In deciding upon the run-off coefficients to be used for tiio Cypress 

 <Teek drainage district the following method was pursued: Atrial 

 coefficient was selected for a small area, one for a me(hum area, and 

 one for a large area, and an algebrai(; expression was then souglii 

 whose curve would approximately fit these platted coefficients. 

 I'he run-offs for interniefhate areas were f hen calculaled and plotted 

 :'nd i\u' r-urve thus ohtaiiu^d was compared with all llie data (h'lived 

 sw.-, -Bull, iwj— in — 2 



