10 BULLETIN 114, U. S. DEPARTMENT OF AGRICULTURE. 
SIZES OF DITCHES. 
The computations of the ditch capacities have been based on the 
Chezy formula for flow in open channels, Y = C-/RS, in which C was 
determined by Kutter's formula, using 0.030 as the value of the 
roughness coefficient "n." Except at the lower end of Boggy Swamp 
and Black Swamp, however, the controlling feature in determining 
the sizes of the ditches has been the method of construction rather 
than the required capacity of the waterway. 
Experience has shown that in heavily timbered lands such as these 
the best type of machine to use is the floating dipper dredge; but 
to float a machine of this kind frequently requires a larger ditch 
than would be necessary to take care of the maximum run-off. In 
lieu of the dredge the only practicable methods of construction will 
be hand labor or explosives; by the former method a ditch of just 
the required size could be constructed, but at a price per cubic yard 
very much greater than for dredge work, so a ditch roughly two 
and one half times the required' size, provided it is no smaller than 
the minimum dredge ditch, could be constructed by the dredge for 
the same cost as by hand labor and in a much shorter time. The 
construction of ditches with explosives is comparatively new, and 
has met with varying degrees of success. It might be well to experi- 
ment with this method on some of the smaller ditches, which are of 
a size best adapted to its use. 
The smallest ditch that can be constructed with a dipper dredge 
of sufficient power to remove the stumps and sunken timbers is one 
with a 14-foot bottom width, 6-foot depth, and side slopes J hori- 
zontal to 1 vertical. Such a ditch would have a top width of 20 
feet. However, to afford proper drainage the depths of the dredged 
ditches should in this case be not less than 7 feet, and therefore 
wherever in this report the phrase " minimum dredge ditch" is 
used it refers to a ditch with 14-foot bottom width, 7-foot depth, and 
| to 1 side slopes. Ditches of this character are proposed for all of 
the main tributary branches except Hurricane Branch, Scott Swamp 
Xo. 1, Ballifore Branch, Kose Hill Branch, Titi Branch, Causeys 
Branch, Long Branch, and Lyas Bay, which streams are too short to 
warrant putting in a dredge. On some of the tributaries the upper 
mile of each ditch should be excavated by hand, as such channels will 
have sufficient capacity and will cost considerably less than minimum, 
dredge ditches. The ditches to be constructed by hand labor, with 
one exception, are recommended to have 3-foot bottom widths, 
5-foot depths, and J to 1 side slopes; such a ditch has an 8-foot top 
width. This kind of ditch will be referred to in this report as a 
''handmade ditch," as all of the ditches not constructed with dredges 
are recommended to be of this size except the upper end of Boggy 
Swamp, which should be 6 feet deep. The excavation for a minimum 
