STRUCTURES USED IN DRAINING AGRICULTURAL LAND 15 
case shown, where the inlets are located opposite each other on a 
narrow canal, a concrete apron extends across the entire bottom. 
For single inlets the outlet structure should be similar to that shown 
in Figure 6. A pipe is connected with a concrete cut-off wall or 
other form of intake structure at the upper end. Where concrete 
culverts or bridges with concrete abutments and wing walls or other 
structures are near such inlets, the lower end of the pipe should pass 
through these walls to obviate the necessity for a special structure 
at the pipe's lower end. If the pipe is to be made up of short sec- 
tions, usually it should be incased with concrete. 
STOCK GUARDS 
Where fence lines cross open drains subject to wide variations in 
discharge, stock guards should be so constructed as to offer but little 
restriction to flow at high stages. Such a guard can Tje made in the 
form of a wooden gate pivoted at each side of the channel, so that 
the bottom will swing downstream about a horizontal axis. 
SLUICEWAYS AND TIDE GATES 
Lands affected to some extent by tides or subject to occasional 
overflow from rivers are protected by levees or dikes. After periods 
of flood the interior water or part of it may* be discharged by 
gravity through sluiceways of various materials, such as wood, 
concrete, and iron pipe. Reinforced concrete usually is best for 
large outlets, which are similar in design to large culverts in soft 
formations. They are usually located near the outlets of large 
sloughs which have been cleaned out and used to store and convey 
the interior water to the sluiceway. The structure should generally 
be located on the bank at one side of the slough where a sump 
may be excavated by a dredge, obviating in many cases the neces- 
sity for cofferdams and also affording better foundation material. 
After the structure is completed channels for inlet and outlet may 
be excavated. 
Gates hinged at the top and placed at the discharge end of the 
sluiceway are better adapted to ordinary practice. In this arrange- 
ment each sluice should be not more than 5 feet in height by 6 or 7 
feet in width, and often smaller dimensions are preferable. To pro- 
vide sufficient waterway several conduits or boxes may be built to- 
gether, and except for small farm installations there should never be 
less than two openings. 
The length of the sluiceways will depend upon the wklth of the 
embankment at its location. For greatest efficiency the elevation of 
the sluiceways should be such that the gates will be submerged at all 
stages of the water. Substantial head and wing walls must be pro- 
vided at each end and the outlet end protected against erosion, 
drift, or ice. Grooves or guides should be provided for emergency 
gates to cut off the water and permit the sluiceway to be drained 
by pumping, inspected, and repaired, and for use in case of damage 
to the tide gate. A trash screen should guard the interior end. 
It has been necessary to support many of these structures with 
piling. Frequently, however, the material under the sluiceways set- 
tles under the weight of the adjoining levee, and when piling is 
