BECLAIMING OVERFLOWED LAIRDS IN MISSISSIPPI. 29 



In computing the capacities of the creek floodways, where the 

 ditches parallel the levees, the discharge of the section represented 

 by IcfgJbk (fig. 9) was computed by takuig the liaefglik as the wetted 

 perimeter for the area, and n equal to 0.030. The discharges of the 

 areas ahJcl and cdef were then computed, taking n equal to 0.040- 

 the siun of these three results gave the total capacity of the floodway. 



CONSTRUCTION. 



No attempt is made here to provide full specifications for the pro- 

 posed work. It is intended under this caption merely to point to 



a . Water' Sur f ace t) 



Fig. 8. — Sketch illustrating method of computing capacity of river floodway, Big Black River, Miss. 



some of the more important details that have governed the design 

 of the improvements and to emphasize those features of location and 

 construction which are vital to the success of the system. 



DITCHES. 



The minimum ditch planned has a bottom width of 6 feet, side 

 slopes of 1 to 1, and a depth of flow of 6 feet; such a ditch can be con- 

 structed economically with the same type of machine that builds the 



^ _ _ b Water Surface C d^ 



m M j.S.H..del 



"^A Channel m 



Fig. 9.— Sketch illastrating method of computing capacities of creek floodways, Big Black River, Miss. 



levees. Ditch No. 4, in district No. 1, can be constructed econom- 

 ically by a floating dredge because its size is sufficient to justify 

 installing such a machine. The width of the berm is independent 

 of the width of the ditch, but varies with the depth of excavation. 

 For cuts of 10 feet or less a berm of 10 feet is planned; for cuts greater 

 than 10 feet a berm of 12 feet is recommended. 



In existing channels, where clearing is the only improvement 

 needed, aU timber and underbrush sliould be cut, all debris removed, 

 and all stumps cut level with the ground. The widths of right-of-way 

 for ditrlies were f/)mj)iitr'd by taking 3^ times the width of the top, 

 plus the width of both berms. 



