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BULLETIN 193;, U. S. DEPARTMENT OF AGRICULTURE. 



structed by floating dipper dredges; the majority of them, therefore, 

 will be much larger than necessary to carry the water that will reach 

 them, and thus will provide large reservoir capacity. The minimum 

 depth was fixed for all ditches at 6 feet, in order to provide (1) suffi- 

 cient depth to float a dredge, (2) adequate outlet for tile drains and 

 field ditches, and (3) better drainage along the ditches before the field 

 drains have been constructed by the individual owners. ' The mini- 

 mum bottom width of ditch for gravity districts was fixed at 2 feet, 

 which is as narrow as it is practicable to make. With bottom width 

 2 feet, depth 6 feet, and side slopes 1 to 1, the top width of the mini- 

 mum ditch will be 14 feet. The bottom widths for minimum ditches 

 in the pumping districts are planned as follows: For the minimum 

 depth of 6 feet, bottom width 12 feet; depths 6^ to 7 feet, bottom 

 width 10 feet; depths 7^ to 8 feet, bottom width 8 feet; depths 8^ to 

 9 feet, bottom width 6 feet; depths 9^ to 10 feet, bottom width 4 feet. 

 With side slopes 1 to 1, the top widths of such ditches will all be 23 

 to 24 feet. In the Appendix will be found a tabular statement of the 

 sizes of the various ditches. 



When constructing the ditches the waste material must be deposited 

 far enough from the edge of the excavation so that the weight of the 

 spoil banks will not cause caving of the sides of the ditch. For all 

 Hunimum ditches there should be a clear berm of 6 feet between the 

 toe of the spoil bank and the edge of the ditch; for ditches having 

 bottom widths greater than the minimum but less than 8 feet, the 

 berm should be 8 feet wide ; and for ditches that have bottom widths 

 of 8 feet or more, the berm should be 10 feet. 



CLEARING RIGHT OF WAY. 



A right of way must be cleared for the ditches located in timbered 

 areas, and the width of such clearing depends on the width of the ditch. 

 The total acreage to be cleared for each district is shown in the cost 

 estimates, the area required for each ditch having been computed on 

 the following basis: 



Widths of right of way to be cleared. 



Top width of ditch. 



Width of 

 clearing. 



Top width of ditch. 



Width of 

 clearing. 



Fed. 



Minimum to 20 



21 to 26 



27 to 33 



34 to 40 



Feet. 



60 



80 



100 



120 



Feet. 

 41 to 46 

 47 to 53 

 54 to 60 

 61 to maximum. 



Feet. 

 140 

 160 

 180 

 200 



