EXPLORING BEAVER HABITAT AND DISTRIBUTION IN CANADA
THE LONGEST BEAVER DAM IN THE WORLD
The longest beaver dam found with Google Earth to date (October 2, 2007) is
located in Northern Alberta. The dam has a length of about 850 meters
(2790 ft). It has at least existed at this spot for over 25 years as
it can be observed on the 1990 Landsat 7 Pseudo Color Imagery provided
by NASA World Wind. However 1980 aerial photo's show that this dam
did not exist yet at that time.
The actual location of the world longest beaver dam (that is until someone finds
a longer one) is just South of Lake Claire, and about 190 km to the
NNE
of Fort McMurray, just inside Wood Buffalo National Park.
Until 2008 Wikipedia listed as the largest dam, a dam near Three Forks,
Montana, with 652 meters (2,140 feet) long, 4.3 meters (14 feet) high
at the
highest
point,
and seven
meters (23 feet) thick at the base. We have not been able to find this
dam on Google Earth.
Jean Thie of EcoInformatics found the beaver dam while using Google Earth to
study environmental change in Canada's Boreal and Sub-Arctic Ecoregions.
He
was looking
in particular for the rate of melting of permafrost in wetlands (typically
occurring as palsas and peat plateaus in Canada's discontinuous permafrost
zone). This type of permafrost occurs in a wetland 2 km to the east of the beaver dam.
The location of the 'longest' beaverdam was first posted on the Google Earth Community Forum on the 5th of October 2007. Since that time no longer dams appear to have been discovered anywhere else, underpinning the original 'tong in cheek claim' that it was the longest beaverdam in the World!'
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Longest beaver dam in the
world found with Google Earth (Digital Globe): October 2, 2007
This dam was measured with the Google Earth Measuring tool to be about 850 meters
in length. There is one major beaver lodge and possibly an older one. No surface water drainage can be seen.
Water moves down the very slight sloping wetland. The (relative
thin layer) of organic material of the wetland works as a sponge
. The flow is slow and over a wide area of wetland which requires
the building of very long dams. Many dams can be found in areas
like this with lengths of 500 meters. Any dam over 600 meter
remains exceptional.
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The aerial photos on the left were provided by Steve Anderson of Wood Buffalo
National Park and appeared in a May 5 article of the Edmonton
Journal by Karen Kleiss: Alberta beaver dam can be seen from
space. (see link).
Of course the dam cannot only been seen from space, it was actually discovered
by 'flying over the earth' with Google Earth. It is unlikely
that this dam would have been discovered without Google Earth
and its high resolution image data base, in this case provided
by Digital Globe.
The actual search strategy was based on a preliminary observation hundreds of
beaver dams across Canada. Based on these observations broad
characteristics
of landscape ecosystems were identified with the highest probability
of high
density
and large beaver dams. These broad landscape characteristics
were used to identify possible target "beaver landscapes". Each
of these would initially be assessed using high resolution Google
Earth images, and exceptional dams would be studied with aerial
photographs available through Canada's National Air Photo Library
in Ottawa The pictures also show near -A- new dams being build which could ultimately join
the main dam and increase the overall length by another 50-100
meters in the next decade.
The Wood Buffalo National Park special web page for the dam provides links to
higher resolution images. We have overlaid these helicopter pictures
directly on ' Google Earth' Below are the KMZ links for these
images. Photo overlay of left image on Google Earth: KMZ link
The second photo and KMZ link shows the substantial size of the beaver lodge.
KMZ Link |
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1975 Aerial photo of the dam area: Some minor beaver activity can be
observed (green arrows) but most of the area is covered by trees
and shrubs. I expect this area was burned about 20-30 years before
the date photos. A even aged stand of stand of poplar (Po) is
visible on the 1970 photo, has been replaced by a wetland in
2005. Of course poplar (Trembling Aspen) is a favorite food source
for beaver and the stand did not survive very long.
This image is part of flight line A24215 ( photo number 253). Date: 9 August,
1975; original scale: 1:50'000.
Aerial photos of Canada can be obtained from the National Air Photo Library (NAPL) |
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| Comparison of the two
images shows interesting elements. The dams 1 and 2 existed in
1970 but have changed very little. The beaver lodge near Dam 1,
has not changed much. Dams 3 and 4 have been build since 1975.
The
beaver
offspring
of dam 4 are building two smaller dams just to the side (green
arrow). Larger images [+] |
The Beaver dam in recent Apple Maps images
In 2007, Google Maps provide relative high resolution images for this area. The actual date of the image on which the beaver dam was discovered is 26 July, 2004. Recently Apple Maps and Bing both have provided higher resolition images for this area. |
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Identifying the best potential beaver habitat with Google Earth
This slight sloping area around the Birch
Mountains was identified as a potential excellent beaver habitat
after the study of a similar environment and beaver community near the Pasquia Hills in Saskatchewan. The NASA LandSat 7 Pseudo Color Image (2005) was taken from World Wind. Relief
is exaggerated 5x to enhance the relief significance for beaver
habitat and occurrence. The alluvial fans and associated drainage
systems provide exceptional habitat. The alluvial fan system
outlined in yellow dots shows a concentration of many large
dams. The black arrow points to the 'longest dam', which is shown
here
by just a small 3-4 mm long thin line dark line.
Some of the high run off areas (purple) appear
less suitable for or preferred by beavers.
This pseudo image with a near infra red band
shows clearly the small open surface water areas representing
(not always) beaver ponds. (Some of the black spots on the slopes
are caused by cloud shadows). |
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The cross section in the figure below is along the white line on the satellite image. The red arrow is at the location of the longest dam. In the elevation profile this is at the line near the 235 m asl mark. The slope profile is typical fo an alluvial fan developed and deposited in a receding galcial lake. Average slope of the wetland in which the beaverdams developed is 0.5%.  |
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The Longest Beaver Dam as Part of a Beaver system. The alluvial fans are fed by a series of streams and creeks from the Birch
Mountains (blue arrows). Because of the very low slope of the
alluvial
fans, drainage flows have shifted and no clear drainage channels
have developed. Beaver dams and ponds identified with light yellow
arrows seem to be inactive. The light blue arrows indicate active
ponds and dams with lodges.
Wave modified strand lines can be seen near
B. Just to the east peat plateaus (P) with collapse scars show the
presence of permafrost in the wetlands. A detailed Digital Globe
image of the peat plateaus around P can be seen at the bottom
of this page (last illustration)
The longest dam is marked
with the red sign.
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The History of the Longest Beaver Dam
The NASA LandSat 7 images of 1990 and 2000
accessible as part of its magnificent World Wind System, give
a simple overview of the beaver ponds and dams since 1990. It
is clear that the this dam (Red Arrow) did exist in 1990 and
had a similar size as in 2000 and 2007 (Digital Globe- Google
Earth). Also it can be observed that the number of beaver dams
increased visibly between 1990 and 2000. Of course the
resolution of the 2000 Landsat imagery is superior to the 1990
Landsat.
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| The Landsat Image below shows the major
wetlands beaver systems just north of the Birch Mountains. Wetland
system 1, 2 and 3 have many large dams 300m to 600 meters in size
with 'the longest dam' over 800 meters in system (1). A few smaller
patches with sizable dams have also been delineated with a yellow
dotted line. Most of these fall within wetlands fed by relative nutrient
rich water flowing from the creeks and streams from the Birch Mountains.
The wetland system (3) seems to have formed in depressions between
the micro topography of the alluvial fan cones. The red lines show
some of the streams with beaver activity, typically very small dams.
Wild land fires are the major reason for the different shades of
green. No fires seem to have been reported for this specific area
since 1980. Larger image.... |
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The figures below show the significant
changes in wetlands system 2 since 1955, the date of the panchromatic
black and white aerial photo. ( Source National Air photo Library).
In 1955 two active dams can be observed (Bd) These dams are still
active on the Digital Globe image: they may be more than 55 years
old. Also since that time an additional 20 dams of varying size were
build.
Fire history may have played a role as well. Most of the burns seem to have happened
before 1955. The most recent one (F1) probably 3-6 years before
the 1955 photo was taken; (F2) 10- 15 years and (F3)15-20 years.
The F4 burn could have the same age as F3. The darker patches between
F1 and F4 are also of fire origin but much older.
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| The Fire History map below shows the
extent of wild land fires between 1980 and 2007. The area outlined
with the red striped line corresponds approximately with annotated
Landsat image
above.
It is remarkable that the area of the beaver dams was not burned
between 1980 and 2007. Particularly since old aerial photos show
widespread patterns of extensive fires before that time. This map
was prepared using the interactive mapping system of the Canadian Wildland Fire
Information System (CWFIS). |
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The Surficial Geology Map of Canada provides a thumbnail sketch of the parent
materials which are present in this area. The white asterix shows
the approximate location. The parent material in the alluvial fan
areas where the dams occur is silty and sandy alluvial material
washed down from the hills and slopes of Birch Mountain and modified
by glacial lake action. |
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The Largest Beaver Dam in the World is actually just inside the boundary of Wood
Buffalo National Park. See the red circle. |
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Topographic map below shows the location of the largest beaver
dam. It is interesting
to see that the contour line near the dam reflect the topography
of the alluvial fans at the bottom of the Birch Mountain slopes |
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The
image below shows other dams in the same area. The longest
is about 400 meters in length. It is also one of the oldest dams in the area. The beaver lodge is clearly
visible as a small 'island' near the centre of the dam.
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The
dam below is almost 600 m in length.
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The
the longest of the dams in this image
is about 430 meters in length. Further 'downstream' -top right- a
new dam is being constructed. The beaver lodges are clearly visible
on this high resolution satellite image. |
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Figure Below: This
unique area of beaver dam is fed with water from the Birch Mountains.
Ultimately
this water also has caused wetlands to develop: the typical bogs
of Canada's North. In cooler times, like the little ice age, and
before, these wetlands developed permafrost in the form of peat
land forms called peat plateaus. The ice formation caused a plateau
like uplifting above the surrounding wetlands. The areas -P- identified
on the image below show peat plateaus with permafrost. The areas
around -nf- are non frozen. Areas identified with -A- show active
melting. Most of the -nf- areas were permanently frozen a few
hundred years ago. |
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![Larger images [+]](images4/longestdamcomparisona1.jpg){kind=link}
