HOW DO BEAVERS AFFECT LOCAL HYDROLOGY AND
DRAINAGE IN THE DOG RIVER WATERSHED?
William W. Cross III,
Department of Earth Sciences, University of
South Alabama, Mobile AL, 36688.
E-MAIL: CBBCross3030@aol.com.
This project examines the positive and negative aspects of beaver dams on a creek or stream. The main negative impact beaver dams have is on the human that builds his home or business near the creek. This work documents beaver dam’s influence on the surrounding environment with detailed photographs of the beaver dam and the surrounding areas. The photographs include the beaver dam itself, downstream of the dam, the reservoir that the dam creates, and the homes that are endangered from the flooding possibility. This research also determines the pH, turbidity, and dissolved oxygen (DO) upstream and downstream from the beaver dam to actually document if the dam’s presence there in fact degrades the water quality. The beavers do not degrade the water quality but really help it, and the only thing that they are hurting is private property owned by humans.
Keyword:
beaver, dam, reservoir
Introduction
Animals that live around our area affect the drainage and local hydrology in the Dog River Watershed, and an animal that is a prime example of this is the beaver. The damming of creeks by beavers in the Dog River Watershed can become a major problem because with the backup of water there is more of a chance of flooding in the local area where the dam is located. The beaver’s natural instinct is to build dams for their homes and to build up a reservoir to supply them with food (Rue III 1964).
Beavers are furry animals with a wide, flat tail that looks like a paddle. Beavers are known for their skill at cutting down trees with their strong front teeth. They eat the bark and use the branches to build dams and lodges (homes) in the water. Beavers live in rivers, streams, and fresh-water lakes near woodlands. They are excellent swimmers and divers. They can swim underwater for a half of a mile and can hold their breath for up to fifteen minutes (Brant 1985).
North
American beavers
(Fig. 1) are three to four feet long, including
the tail, and can weigh from
forty to sixty pounds. They are the
largest rodents (gnawing animals) in the world except for the capybara
of
The beavers
are the
guardians of our water. By damming
streams beavers raise the water level, spreading it laterally across
gently
sloping valleys, slowing its erosive force, and increasing the amount
of water
held in soils. The additional water
increases both the amount and productivity of plants, and the kinds and
numbers
of animals, particularly fish (USDA Forest Service 1999).
A beaver uses its strong front teeth to cut
down trees and to peel off bark and the branches (Fig.
2). The beaver stores some branches
deep in the
water for use as food during the winter.
The other branches may be used to enlarge or repair the dam and
the
lodge (Brant 1985).
Beavers are one of the few mammals, aside from humans, that can profoundly change their habitats. The dam is started by laying parallel sticks and branches in the streambed, the butt ends facing upstream so that the current anchors the spreading branches more securely in the bottom. The first layer is then plastered with stones, roots, and mud; and again the current aids in packing the silt into the spaces between the leaves and twigs. The dam is built up high enough to hold back a pond six to eight feet deep. The average finished dam is usually about fifty yards in length, six feet high, and about nine feet through the base (Banfield 1987).
There is a big debate over whether beaver dams are a hindrance to people living near creeks. Beavers, however, can be beneficial to the environment. The benefits of having a beaver dam blocking a creek flow are that it helps control erosion; it reduces sedimentation in streams and rivers, and helps develop new wetlands. These dams also help the wildlife by increasing the biodiversity because they create a better environment for fish and waterfowl, a more stable water supply for wildlife and vegetation, ground water recharge and ground water table elevation and formation of natural lakes and ponds (Beaver Dam Information Site 2004). The disadvantages that are argued are that the beaver dams are hurting the fish, causing flooding in residential areas, and destroying non-aquatic vegetation by the increased reservoir.
There are new policy changes that have resulted from the people that believe beavers are a hindrance instead of a benefit. The state’s Animal Damage Control agents have started to lethally remove the beavers, rather than live- trap and release them to a safer location away from the public. Does the lethal removal of these beavers have to be done? The usual plan to restore a river and its tributaries is to get rid of or destroy all dams (man-made or animal generated) to help support river restoration (Holyoke 2004), but does the placement of these dams help these fragile ecosystems survive?
The beaver’s return
has generally
been beneficial to wildlife because of the additional wetland habitats
they
create. The habitat that the beaver dam
creates has aided in the return of the wood duck, a species that was
near
extinction at the turn of the century.
Unfortunately, the beaver’s return has created problems for a
number of
landowners. Economic estimates of beaver
damage in
Animal Control has
implemented
trapping the beaver as an effective means to reduce the beaver
population,
especially if the beaver has caused damaged to human owned equipment or
land. The Conibear
330 (Fig.3) is the best trap available for
catching and killing the southern
beaver. This trap usually kills
instantly and is almost 100 percent effective in preventing escapes. Other equipment used in catching and killing beavers is the snare, leghold
traps, and shooting has shown to be successful (Armstrong Undated).
Current evidence of a beaver dam is
in the section of Rabbit Creek that crosses
Research Question
Is the killing of beavers and destroying the dams they create actually helping the environment and wildlife or just getting rid of a nuisance because of the problems that could affect people living around the dam? The significance of the answer to this question is if the community left the beaver dams alone, would it end up helping the environment and rejuvenating the watershed?
Methods
First, my research question led me
to take documentation of the beaver dam to see how the environment was
being
changed with the presence of the obstruction (Fig.
5). Secondly, I
measured the stream width by
pacing along the roadway for both sides of the stream to see how much
the water
in the area has increased from the time the beaver dam was put into
place. I then took the measurement I got
from the
reservoir and compared it to the measurement that I got for the normal
stream’s
width that was located on the other side of
Results
The results from
the documentation
are that I saw that the reservoir (Fig. 6) made
the stream exponentially grow
much wider because of the water that was trapped behind the dam. The documentary photographs help to show how
much the creek has widened because the beaver dam has impeded the flow
of
water. The measurement of the outflow
part of the creek or the normal size of the creek was twenty-four feet
long in
width. The reservoir that the beaver dam
created is about seventy feet long in width so the beaver dam flooded
about
fifty feet of land after it was built.
The beaver dam length was about twenty-five feet to thirty feet
long. The distance the house from the
water was
about thirty feet and the elevation I estimated was about ten feet, so
the
danger is very minimal (Fig. 7).
This is
probably why the residents have not taken any action on removing the
beavers or
the beaver dam.
The test results of my water
quality can be seen in Table 1.
The pH was the same for both sides, and the
pH was acidic probably because runoff from acidic soils and the
decaying
vegetation. The turbidity was probably
different because the water was flowing over the beaver dam and causing
the
soil from the bottom of the creek to get agitated and float to the
surface. The temperature of the water is
important because it affects how much dissolved oxygen the water can
hold and
how quickly nutrients will be cycled through the creek system. The dissolved oxygen and saturation levels
for both sites were really low because the beaver dam’s expansion
caused plants
to die and when they rot they take oxygen out of the water (Alabama
Water
Watch: Water Chemistry Monitoring 2002).
Discussion and Conclusion
The main points of this project are
that needless killing of beavers should stop and that knowledge about
the
benefits of beaver dams for wetlands should increase.
The beaver dam does create a huge reservoir
that covers a lot of used or unused land, and sometimes if the land is
being
used the dam can create a lot of problems for the people who own the
land. This action of leaving the beaver
dams in
place would help the Dog River Watershed because the wetlands will be
able to
grow and rejuvenate, but there are always problems when a species lives
on
creeks that flow in urban areas. The
beaver dam is a great attribute to any stream or creek because it will
rejuvenate it to where it was before man altered it.
But if the beaver dam is located in an urban
area where the rising water could produce a problem for the residents
that live
near it, the beaver dam will be removed and the creek will suffer.
Bibliography
Armstrong, James B. Beaver
Control in
Banfield, A.W.F, The Mammals of
Beaver Dam Information Site. Available: <www.beaverdam.info>
Accessed:
Brant, Daniel. The World Book Encyclopedia. Beaver, 1985.
World Book Inc.,
Holyoke, John. Burgeoning Beaver Dams Hurting Fish.
Rue III, Leonard L., The
World of Beaver.1964, J. B. Lippincott
Company,
