18 
BULLETIN" 193^ U. S. DEPAETMENT OF AGEICULTUEE. 
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 xoinimum 
depth was fixed for all ditches at 6 feet, in order to provide (1) suih- 
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 fset, 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 foUows: 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 mdths of such ditches will all be 23 
to 24 feet. In the Appendix wiU be found a tabular statement of the 
sizes of the various ditches. 
BERMS. 
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 wiU not cause caving of the sides of the ditch. For all 
minimum 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 EIGHT 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 
tlie following basis: 
Widths of right of way to he cleared. 
Top width of ditch. 
Width of 
clearing. 
Top width of ditch. 
Width of 
clearing. 
Feet. 
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 
