L
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A PROGRESS REPORT
on
A TECHNIQUE TO CONTROL WATER LEVELS IF
BEATER IMPOUNDMENTS
by
ROGER S. LEIGHTON AND JAMES A. LEE
NEW HAMPSHIRE FISH AND GAME DEPARTMENT
CONCORD, NEW HAMPSHIRE
The past decade in New Hampshire has seen the beaver increasing in
all regir_ns of ths
ate
With this increase in the beaver population has
naturally come the creation of many impoundments, These impoundments have,
in many instances, proved to be valuable waterfowl breeding and resting
areas. Summer brood censuses carried on by the Departments biologists
have consistently shown beaver flowages to be producers of black ducks
and wood ducks. The increase in beaver has also provided additional
revenue to trapners as regulations become more relaxed.
An increasing beaver population has, however, brought many problems, not the least of which is the damage to roads, cultivated lands and
timber, as a result of the high water level maintained in these imnoundments. The natural tendency of interested Parties in these cases has been
to call for the removal of the beaver from the affected area
This has
resulted in the beaver being killed or live trapped and the subsequent
deterioration of the impoundment.
Quite often the dam is torn out or
blasted with dynamite to hasten the reduction of the water level and
relieve the damage caused by the impounded water.
As a result, of tns.se actIons many beaver created waterfowl areas
have been lost when, if the proper water level could have been maintained
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no damage would have resulted and the duck habitat saved.
It was with this thought in mind that the N. H. Fish and game
Department first began to experiment with perforated drain pipe as a
method for controlling the water level in a beaver pond. This experimental
work was started in October; 1948.
In the interest of economy it was decided that "Bermico" fibre
ripe would be used. Two eight—foot sections of four—inch fibre pipe were
joined by a flexible fibre coupling and installed through a...beaver dam
where the impounded water was causing damage. Three—eighths inch holes
were drilled in the area comprising the bottom 60'of the pipe The pipe
was fastened in place where it passed through the dam and the upstream end
left unplugged. The pipe was so installed as to lower the water level
approximately six inchee) By the middle of November an inspection revealed
the water level to be dcwn to that of the pipe, which was the level desired.
This inspection also brought to light many of the inadequacies in this type
of an installation. Beaver standing on the unsunnorted upstream end or the
accumulation of beaver deposited debris was able to break the pine at the
coupling. The unplugged upstream end of the pipe allowed the beaver to
shove woody material into it thus serving to make the nine inoperative
The pipe was found to be inadequate to take care of more than the minimum
runoff.
In June 1949 a second experimental in.stallation was started in a
drainage ditch which had been dammed by beaver to create an impoundment of
ten acres. As in the first experiment, two eight—foot sections of four—
inch perforated pipe were connected with a fibre coupling. Approximately
ten feet protruded upotream and the remaining six feet extended downstream
through the dam. In this experiment the upstream section of the pipe was
-3suspended sixteen inches from the bottom (the desired water level) by
means of dried oak posts secured with baling wire. Also, the urstream end
of the pipe was plugged with a four—inch wooden disc. A later inspection
revealed the beaver had gnawed the posts off below the pipe. This resulted
in the two sections of the pipe separating at the coupling. The beaver
then succeeded in filling the section of the pipe which ran through the dam
with sticks and mud, making it inoperative. The pipe was torn out and replaced by three new eight—foot sections4 In addition to the regular three—
eights inch holes, six one—inch holes were placed on the underside of the
upstream section of pipe. The pipe was again suspended sixteen inches from
the bottom by means of two iron stakes driven into the substrate. The eight—
foot sections were securely fastened together by nailing the fibre coupling
to the pipes, then nailing cleats over the coupling to give added strength.
The upstream end of the pipe was plugged as before. This second experimental
installation proved very successful. The beaver renaired the gap made in the
dam where the pipe was installed. This failed to bring the water level up to
their needs so they resorted to extending the wings of the dam. This also
failed to raise the level as the perforated pipe continued to keep the
water at the desired level,
Other experimental installations were made throughout the state,
each one having certain modifications to make it more successful.
More
attention has been raid to using the correct size and number of pipes RS
well as providing an adequate number of perforations. In installations of
a more permanent nature, the pipes were designed to take care of at least
a portion of the maxmum expected runoff. Preliminary reconnaissange,:of,the
impoundment provides an opportunity to measure the current volume of flow
and to obtain field data necessary for determining the maximum exrected.
-4runoff. Knowledge of these factors is necessary in determining whether
perforated pipes are a practical means of controlling the water level. In
cases where the volume of flow recorded is substqntial it has been possible
to install pipes capable of handlin7' this flow and only a small portion of
the runoff. In instances where the volume of flow has been slight, it has
been possible to install Pines capable of handling Ire to one-half of the
expected runoff. The authors have drawn up tables which permit auick determination of the size and number of Pipes needed and the proper size and
number of perforations required to do the job.
In order to prevent beaver from completely burying the pipes in
installations where the pipes extend through road culverts, it was found
advantageous to place a barbed-wire entanglement around the installation.
Pipes having these barbed-wire entanglements, when inspected later, were
found to be in operation even °though the beaver had deposited sticks, brush
and mud atop the wire entanglement. As these entanglements have been used
in a limited number of instances in New Hamnshire, their value has not
been fully ascertained and more experimentation is necessary to determine
their value.
More installations are scheduled this year at which time the
authors will have further opportunity to test various modifications designed to make the installations more successful.
CONCLUSION: The use of perforated pipes installed through a
beaver dam promises to furnish the game manager with a simple, and in
most instances, successful method of controllinc, water levels in beaver
impoundments. Limited experimentation in New Hampshire has pointed out
its potential value as a means of Preserving beaver impoundments through
control of the water level.