12 BULLETIN 198, U. S. DEPARTMENT OF AGRICULTURE. 



MISSISSIPPI RIVER COMMISSION PLAN. 



The plan of the Mississippi River Commission, made in 1907, pro- 

 vides merely for the diversion of Cypress Creek in order that the gap 

 in the levee may be closed, and makes no provision for the further 

 drainage of Desha County. The suggested course of the diversion 

 is through Boggy Bayou, Boggy Lake, Clay Bayou, and Clay Bayou 

 Wash into Macon Lake in Chicot County. The plan provides for 

 2,300 second-feet of flow at Boggy Cut-off and 3,150 second-feet 

 above Macon Lake, requiring a channel of 60 to 80 feet in bottom 

 width, with side slopes IJ horizontal to 1 vertical, flowing 11 to 11^ 

 feet deep. 



The area drained by Cypress Creek is approximately 413 square 

 miles, and that by Clay Bayou about 582 square miles. Using the 

 drainage coefficients determined from figure 5, the capacity of the 

 diversion channel should be 5,300 second-feet at Boggy Cut-off and 

 7,050 second-feet at Macon Lake. In order to obtain a proper 

 fall in the ditch and to give drainage to the upper district, it would be 

 necessary to hold the high-water surface in this diversion channel 

 3 to 4 feet below ground level. Since 15 to 16 feet is about the 

 deepest economical excavation, the depth of flow should be about 

 12 feet. The required channel would then be 140 to 185 feet, 15 to 

 16 feet deep, with 1 to 1 side slopes. There are two reasons for reject- 

 ing this plan in favor of the ditch plan recommended: First, the cross 

 section of the necessary channel is too great for the most economical 

 construction; second, it will not serve effectively as the main drainage 

 outlet for the district, principally because of the high banks along 

 the larger tributaries. It has no advantage over the plan herein 

 recommended. 



FLOODWAY PLAN. 



A system involving a combination of ditches and floodway was 

 worked out in detail. Tliis plan provides for carrying the drainage 

 from Wells Bayou, Cypress Creek, and Oak Log Bayou through a 

 floodway from Amos Bayou, in sec. 30, T. 10 S., R. 2 W., to Bayou 

 Macon near Mc Arthur. From here the channel of Bayou Macon was 

 to be cleared as in the recommended plan. The drainage from a small 

 area at the head of the Coon Bayou watershed would, under this plan, 

 be diverted into the head of Bayou Macon. The remainder of the 

 Coon Bayou drainage was to be carried under the floodway to the 

 ditches in the eastern part of the district. 



The floodway would be a canal 90 to 200 feet in bottom width, 

 excavated 5.5 to 23.7 feet deep, with levees on each side 4.5 to 13 feet 

 high, except at the banks of Amos Bayou and Bayou Macon, where 

 no levees would be required. The total earthwork for this floodway 

 was computed to be 2,186,000 cubic yards, which is estimated would 



