26 



BULLETIX 724^ U. S, DEPAETMENT OF AGEICULTURE. 



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, because 

 the latter always 

 must be large 

 enough to make cleaning practicable, and the formei- usually are 

 designed to provide the necessary capacity for drainage only. Figure 

 10 shows a U-shaped head wall sometimes used for side-hill culverts 



SECTION 

 CATCH BASIN 



Fig. 9. 



