22 U. S. BUREAU OF FISHERIES. 
only expensive, but they are also frequently a subsequent source of 
annoyance, expense, and loss of fish, when damaged as the result of 
freezing and thawing. It is worthy of special comment, therefore, 
that H. L. Canfield, superintendent of fish culture at the Fisheries 
biological station, Fairport, Jowa, has devised a type of pond outlet 
which has been found, after long trial, to be both relatively inex- 
pensive of installation and convenient and enduring in operation. 
The Canfield L outlet, here described and illustrated, provides both 
for all ordinary overflow and for draining the pond as easily and 
quickly as with the concrete outlet. 
The outlet consists of two pieces of threaded pipe of required length screwed 
hand-tight into an elbow. When connected for service one pipe is joined to the 
dra nage line, and the other, the elbow acting as a hinge, becomes a movable 
standpipe, the raising and lowering of which controls the depth of the water 
in the pond. A pipe stop about 2 feet high is arranged back of the elbow to stay 
the standpipe from passing the center. 
Two or three cement blocks about 2 by 2 by 2 feet are set about the drainage 
line to anchor it and to give protection to the embankment against animals 
and water seepage leading into it along the line. These blocks serve also as 
couplings for the joining of the pipe to the drainage line and for other con- 
nections in the line as desired. When a kettle is used one block joins a side 
of it, anchoring the pipe connection with the drainage line and serving as a 
base for a walk support. A second block is placed about the drainage line 
approximately beneath the top and inside edge of the embankment. This is 
usually a drainage line connection block. If the drainage line passes entirely 
through the embankment a third block should be placed around it several feet 
into the embankment from the outside. 
The outlet screen consists of a half coupling (whole coupling if desired) .with 
a quarter-inch groove around it 2 inches below its top, to which is attached, 
by means of galvanized wire, a covered cylindrical screen of desired mesh, 1 
foot high. This is screwed to the outlet pipe. A cylindrical or square screen 
of large proportion may be installed about the standpipe if maximum screen 
area is needed, although for general use this will not be required. 
A cement kettle 12 by 6 by 1 feet set parallel to the embankment, and within 
this kettle a small kettle about 15 inches wide, 3 inches deep, and about 7 
feet long (long enough and wide enough to admit the standpipe with screen, 
when down level) are used at Fairport with the L outlet. The drainpipe 
enters the side of the main kettle about 6 inches from the elbow and 1 foot 
from the end. The bottom of the inner kettle is made level with the base 
of the outlet pipe when it is down level in position to drain, and provision is 
made for the removal of the elbow by cupping out the cement beneath it and 
filing the space with clay, to prevent the trapping of fish when the pond is 
drained. The main kettle has a slight rise from the inner kettle to the sides 
to provide drainage. 
A walk of 2-inch plank supported by 2 by 4 inch stringers is made to extend 
from the embankment to within a foot of the outlet screen, the stringers 
resting about 6 inches above the top of the outlet pipe when erect. This walk 
rests on two pipe supports which extend from the cement blocks in the drain- 
age line. 
The standpipe is chained to the sides of the outer walk support by a piece 
of galvanized pump chain the length of the distance the pipe travels. This 
chain passes through a loop eye in the post and is provided with a ring larger 
than the eye, so that the end of the chain can not be drawn through. By means 
of this chain the standpipe may be raised and lowered and the level of the 
water in the ponds adjusted and held as desired. An ordinary lock, or an iron 
bolt may be used to secure the chain in the loop. 
Malleable iron pipe is excellent material for the outlet, but ordinary black 
steel pipe is cheaper and gives good service. One piece of pipe of required 
length for the standpipe, threaded both ends, an elbow, and about 2 to 23 
feet of pipe threaded one end, to serve as connecting pipe with the drainage 
line, are all the materials required for the outlet. It is recommended, how- 
ever, that metal pipe be provided from the elbow well into the embankment 
for the better protection of the drainage line. Eight-inch pipe is recommended 
for ponds of 1 acre in area and proportionately smaller pipe for smaller ponds. 
