STRUCTURES USED IN DRAINING AGRICULTURAL LAND 
19 
lines make possible a supporting structure of greater stability. Pro- 
vision for breaking the force of waves against the outer end 
should be made as shown in the illustration. 
The gates must of necessity be at the land end. The gate cham- 
ber should be reinforced concrete supported with piling and should 
be divided into as many sections as there are outlet pipes. Grooves 
adjacent to the outlet pipes are desirable to accommodate flash 
boards for an emergency gate. Figure 13 shows self-acting iron 
tide gates, but lumber gates properly balanced might serve very 
well. The design shown is similar to the Oxnard outlet in that two 
gates for each outlet pipe are used. Where the outlet pipes are 
Air Vents 6" Pipe ■ 
---204' Pile Bents 6' apart-] 
- - 10 Gauge 60" Com. Pipe — j 
Mean Sea Level US.C.&G.S 
Gate 
House- 
-44- 2 4 2' Without Pile Supports 
Outlet structure into ocean 
less than 5 feet in diameter one gate for each, of proper size, will 
be sufficient. Cut-off walls of sheet piling should extend out a con- 
siderable distance beyond the ends of the wing walls, and a trash 
rack must be provided. 
BRIDGES AND CULVERTS 
Bridges and culverts are among the most expensive structures used 
for open drains. 
Permanent structures of steel, concrete, or treated timber are re- 
quired for railway or primary road crossings and must conform to the 
requirements of the railway or highway system on which they are 
built. The bed and banks of ditches are subject to considerable 
