26 
BULLETIN 724, U. S. DEPARTMENT OF AGRICULTURE. 
PLAN 
Movable 
fall to clear. One-quarter inch to the foot, or about 1 in 50, will be 
sufficient under all usual conditions. Of course the pipe should 
be designed according to the proposed slope. Whatever specifica- 
tion is used for or- 
dinary pipe c u 1 - 
verts, cementing the 
joints under no cir- 
cumstances should 
be omitted when 
drop inlets or catch 
basins are used, on 
account of the pos- 
sibility of operation 
under head. 
The materials or- 
dinarily used in 
constructing drop 
inlets and catch 
basins are Portland 
cement concrete, 
brick, or stone. 
Figure 8 shows a 
design for a drop 
inlet constructed of 
concrete and figure 
9 a catch basin con- 
structed of brick. 
The only essential 
difference between 
the catch basin and 
the drop inlet is in 
the space below the 
end of the culvert 
pipe which is pro- 
v i d e d to collect 
sediment. Drop in- 
lets usually are 
somewhat smaller 
than catch basins, 
however, b e c a u s e 
the latter always 
must be large 
former usually are 
ainage only. Figure 
SECTION 
CATCH BASIN 
Pig. 9. 
enough to make cleaning practicable, and the 
designed to provide the necessary capacity for di 
10 shows a U-shaped head wall sometimes used for side-hill culverts 
