The strainer on the suction hose is
the intake strainer by building a dam
placed at least 4 inches below the
as shown in figure 4.
In swiftly
water level.
This precaution reduces
flowing streams, a wing or baffle dam
the
possibility
of
the
strainer
can be constructed to protect the
becoming clogged with floating debris,
intake screen without impounding the
or the loss of prime owing to air
water (fig 5).
entering the suction line.
e. Floats.
Floats made of logs,
3.
INLAND SURFACE WATER SOURCES
lumber, sealed cans, or empty fuel
drums can be used to support the
a. Advantages.
For normal field
intake strainer in deep water.
They
water supply, surface water is the
are especially useful in large streams
most
accessible
and
most
easily
where the quality of the water varies
developed water source.
This source
across its width or where the water is
also lends itself readily to the
not deep enough near the banks to
purification equipment common to most
cover the intake strainer. The intake
engineer units.
Various methods of
point can be covered by an adequate
constructing intake points for inland
depth
of
water
by
anchoring
or
surface water sources are discussed in
stationing the float at the deep part
b through g below.
of the stream. The intake hose should
be secured to the top of the float,
b. Rocks and stakes. If the stream
allowing enough slack for movement of
is not too swift and the water is deep
the float.
If support lines are used
enough, an expedient intake may be
to secure the float to the banks, the
prepared
by
placing
the
intake
position of the float can be altered
strainer on a rock. This will prevent
to correspond to changes in depth by
clogging
of
the
strainer
by
the
manipulation of the lines.
The chief
streambed and provide enough water
advantage of a float intake is the
overhead to prevent the suction of air
ease with which the screen can be
into the intake pipe.
If the water
adjusted.
Figures 6 and 9 illustrate
source is a small stream or shallow
two types of improvised floats.
lake the intake pipe can be secured to
a post or pile as shown in figure 1.
f. Galleries.
Water from muddy
streams can be improved in quality by
c. Pits.
When a stream is so
digging intake galleries along the
shallow that the intake screen is not
bank. A trench is dug along the bank
covered by at least 4 inches of water,
deep enough so that water from the
a pit should be dug and the screen
stream percolates into it to intercept
laid on a rock or board placed at the
ground
water
flowing
toward
the
bottom of the pit.
Pits dug in
stream.
The trench is filled with
streams with clay or silt bottoms
gravel to prevent the sides from
should be lined with gravel to prevent
collapsing.
The intake strainer is
dirt from entering the purification
placed in the gravel below the water
equipment (fig 2).
The screen is
line (fig 7).
The amount of work
surrounded by gravel which prevents
required to produce the gallery is
collapse of the sides of the pit and
justified by a reduction in the amount
shields the screen from damage by
of chemicals needed to coagulate the
large floating objects.
The gravel
water,
the
elimination
of
the
also acts as a coarse strainer for the
necessity of frequently backwashing
water.
A similar method may be
the filter, and the higher quality of
provided
by
enclosing
the
intake
water obtained.
screen in a bucket or other container
as shown in figure 3.
g. Drive points.
Many times it is
advantageous to utilize shallow ground water
d. Dams. The level of the water in
small streams can be raised to cover
3-6
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