24 BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 
sectional dimensions of the proposed ditch should be known and the 
relative amount of each class, also the width of berm and the side 
slopes. On small ditches the spread of the spud feet usually deter- 
mines the width of berm. The total amount of excavation, nature 
of the material, and whether the dirt is to be dumped on one or both 
sides are factors that must be considered. A knowledge of the depth 
of water which can be maintained at a minimum expense is also 
necessary, and information as to the number and size of stumps to be 
encountered is of the highest importance. Owing to the expense of 
knocking down, transporting, and setting up a dredge, it is necessary 
to select or use one of the size that will do the most work at one 
building. This requires intimate knowledge of the layout of the 
proposed work and of the accessibility of the different portions. 
The size of ditch best fitted for any size of dredge is one which 
gives just sufficient clearance for the moving of the dredge. ‘The 
ditch, at its top, should be about 4 feet wider than the hull of the 
dredge. 
It is the opinion of many contractors that the use of dredges with 
hulls 18 feet wide or less is to be avoided, except where the ground 
is so hard that the bank spuds rest firmly and bear the weight of 
the swinging load; in soft ground it may be cheaper to use a wider 
hull, even though it is necessary to make the ditch wider than speci- 
fied. 
To determine the particular dredge required for a project, it is 
necessary to know the limitations of the various sizes of machine 
and the distances a machine of a given length of boom and dipper 
handle will dig below water line and dump above water line. The 
hull, of course, must be of such dimensions as to accommodate ma- 
chinery of the required dimensions. Table 10 gives the approximate 
dimensions of different sizes of dipper dredges equipped with differ- 
ent types of bank spuds. The dimensions vary somewhat for different 
makes of dredges. The size of hull can be varied to suit the needs of 
the particular job. When material is excavated it swells and occupies 
more space than before removal. The amount of swell varies, with 
the excavated material, from 10 to 25 per cent. The angle of repose 
of the excavated material varies with the character of that material. 
It is usually taken as a 1 to 1 or 13 to 1 slope, but in soft, wet ma- 
terial the angle of repose is much flatter. 
