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The engineering in beaver dams

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Before their near extinction, beavers populated the smaller rivers in Eurasia and North America. Beavers are called ‘ecosystem engineers’, since their dam building activities dramatically change the character of river (flow characteristics, groundwater and morphology), river habitats and ecosystems. The largest dam currently in existence has a length of 850 m, raising the question of the engineering required for such large structures. A research programme was initiated at Southampton University to assess the engineering importance, and char-acteristics of beaver dams. It was found that the dams are built in rivers of up to 45 m width. They modify the flow duration curves, increasing ground water retention, reducing the gradient and sediment transport, trap-ping sediment and improving ecosystems. Model tests were conducted to investigate the strength and perme-ability of beaver dams. It was found that beavers employ interesting construction techniques, creating semi-permeable dams able to withstand flow volumes of up to 1.34 m3/s per meter width for a 1.4 m high dam. Beaver dam technology may allow to create novel, nature based solutions for ecosystem redevelopment and river renaturalisation.
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1 INTRODUCTION
1.1 General characteristics of beaver dams
With a length of up to 1.2 m, and weights from 22 to
30 kg the beaver is the second largest rodent in the
world. Only the South American Capybara (Hydro-
choerus hydrochaeris), with weights of 35 to 66 kg,
is larger. There are two subspecies, the Eurasian
Beaver (Castor fiber) and the American beaver
(Castor canadensis) which are however very similar
in appearance. Beavers lead a semi-aquatic lifestyle,
and build dams in creeks and smaller rivers in order
to create a habitat for themselves. These dams can be
impressive structures. Fig. 1 shows a 2.5 m high dam
in Kanton Zurich, Switzerland.
The Eurasian beavers inhabited rivers from Portu-
gal to Kamchatka, and from Norway to Syria and
Northern Iran. They were however hunted to near
extinction already in the 16th century, and only small,
local populations survived in a few remote areas. In
Europe, there is little or no collective memory of
what beaver engineered riverscapes look like. Rein-
troduction programmes in several European Coun-
tries were initiated in the 1920s, and by now there
are growing populations in Sweden, Germany, Aus-
tria etc. In North America, beavers were also near
extinct in the 1930s. Again, protection measures
helped to redevelop populations. The construction
activities of beavers modify river valleys and their
ecosystems to an extent that completely new habitats
are created. Beavers are therefore termed ecosystem
engineers’.
Fig. 1: Beaver dam in Switzerland (with permission)
They are also considered a keystone species’,
since their existence has a disproportionately large
influence on the ecosystem they inhabit. Beavers
have lived in our river systems for 24 million years,
so that the river environments, ecosystems and spe-
cies evolved and developed within their engineered
landscape, Rybczynski (2007).
The scientific literature on beaver dams comprises
several hundred articles and books see e.g. the over-
view in Burchstedt (2013). It is however practically
exclusively written by biologists and geo-ecologists.
Despite the apparent technical aspects, such as the
dam’s strength, the importance of beaver dams e.g.
in the context of river hydraulics, morphodynamics
The engineering in beaver dams
G. Müller & J. Watling
University of Southampton, Southampton, UK
ABSTRACT: Before their near extinction, beavers populated the smaller rivers in Eurasia and North
America. Beavers are called ecosystem engineers, since their dam building activities dramatically change the
characteristics of river systems, and connected habitats and ecosystems. The largest dam in existence has a
length of 850 m, raising the question of the engineering required for such large structures. A research pro-
gramme was initiated at Southampton University to assess the engineering importance, and characteristics of
beaver dams. The dams are built in rivers of up to 45 m width. They modify the flow duration curves, increase
ground water retention, reduce gradient and sediment transport, trap sediment and improve ecosystems. Model
tests were conducted to investigate the strength and permeability of beaver dams. It was found that beavers
employ interesting construction techniques, creating semi-permeable dams able to withstand flow volumes of
up to 1.34 m3/s per meter width for a 1.4 m high dam. Beaver dam technology may allow to create novel, na-
ture based solutions for ecosystem redevelopment and river renaturalisation.
and management, or the question of what a natural
river actually looks like, only one paper has to the
authors’ knowledge so far been published on their
engineering aspects, Müller (2014). Details of engi-
neering relevance are only sporadically mentioned in
the literature. A research programme was therefore
initiated at the University of Southampton to assess
the engineering aspects of beaver dams and their ef-
fects on river hydraulics. The first step was a litera-
ture review to find quantifiable information such as
the main dimensions and boundary conditions. From
the literature, they could be determined as follows:
1. Length: 1 to 850 m, Geostrategies (2007)
2. Head difference or height: 0.3 to 5 m; most
dams are however below 1.5 m high.
3. Width of river: up to 46 m, Pollock et al.
(2003), the majority of dams is however located
in 4th order streams with widths of 10 m or less,
Naiman et al. (1988).
4. Gradient: most dams are built in streams with
gradients of 0.06 or less. Dams are also reported
in steeper streams with gradients of up to up to
0.12, e.g. Retzer et al. (1956).
Information about the flow volume of the rivers
with beaver dams is unfortunately usually not men-
tioned. From the descriptions, it can be estimated
that beaver dams are built in streams even with very
low average flow volumes of 0.01 m3/s. There is no
information available about the upper limit of aver-
age flows. A width of 45 m suggests flow volumes
of 10 to 15 m3/s. Here it should however be noted,
that the presence of beavers and beaver ponds has a
strong influence on average and minimum flows due
to their effect on ground water recharge and water
retention. In particular low flow volumes increase
when beaver dams are present.
In North America it is estimated that before the
settlement by humans, approximately 25 million
beaver dams existed, i.e. 1.5 dams per square kilo-
meter, Pollock et al. (2003). In Europe, a similar
density could be expected. The number of dams per
km river length is a function of the gradient and es-
timated as 2.5 to 10 per km. It appears that in a natu-
ral river landscape, beaver dams exist in virtually all
smaller rivers.
1.2 Hydraulic effects
Beaver dams modify the hydraulics and hydro-
morphology of rivers:
1. Pond formation: the rivers are changed into a suc-
cession of river channels, beaver ponds and wet-
lands. The pond area here can range from several
dozen square meters to several hectares.
2. Ground water level: The rise in water level caused
by the beaver dam generates a local increase of the
ground water level. The increased wetted area leads
to an increase in ground water recharge. This again
causes changes of the vegetation, as well as a reten-
tion of water and a dampening of seasonal flow vari-
ations.
3. Flow: in particular in arid zones, it was observed
that after the introduction of beavers, streams which
were seasonal and ran dry during the summer be-
came perennial, e.g. Naiman et al. (1988).
4. Retention: beaver ponds and wetlands retain wa-
ter, and can therefore reduce the peak flow during
flood events.
5. Erosion and incision: the dams reduce the effec-
tive gradient of rivers, and thereby their dynamics
and erosive tendencies. In rivers where beaver dams
were removed, incision began, leading to a lowering
of the river bed and ground water level, e.g. Pollock
et al. (2014).
1.3 Morphological effects
Beaver dams slow down flow velocities in rivers and
thereby lead to the deposition in particular of fine
sediment. The low depths of the beaver ponds com-
bined with the removal of trees by the beavers lead
to the production of significant amounts of biomass,
which again is also deposited in the ponds. Dams are
subsequently increased in height to maintain water
depth in the ponds, so that the length of dams in-
creases with time. Geologists have argued that bea-
ver dams permanently formed river valleys,
Ruedemann and Schoonmaker (1938). Studies
showed that depth erosion and incision of small
streams in North America only began after settle-
ment of the land by Europeans, and after the disap-
pearance of beavers, Mackie (2011).
1.4 Ecological effects
As ecosystem engineers, beavers modify the envi-
ronment substantially. Habitats within the areas of
the ponds, in the wetlands created by the increasing
ground water level and further away are changed.
The habitats around beaver ponds and wetlands dif-
fer substantially from those near rivers without bea-
ver dams, Collen and Gibson (2000). The number of
species and individuals in beaver engineered rivers is
significantly larger than in those without beaver ac-
tivities. In particular amphibious species find habi-
tats which would otherwise not exist on fast flowing
rivers, Dalbeck and Weinberg (2009).
1.5 Longevity and dam failure
The longevity of beaver dams ranges from several
months to several decades. Recent comparison of
historic records, and the present situation in the
Great Lakes Region (USA) showed that some dams
can last 150 years, Johnston (2015). There appear
however to be intermediate periods of abandonment
and decay of the dams, probably caused by the dete-
rioration of the food supply. The temporal dynamics
of beaver dams and their effects on river hydraulics
and ecosystem seem to be another interesting topic
in the assessment of natural rivers. Although failures
of beaver dams occur frequently, more detailed in-
formation about the conditions leading to failure are
rare. Westbrook et al. (2006) report the failure
(breaching) of an 8 m long, 0.8 m high dam (“upper
dam”) made of alder and willow stems during a flow
of 8 m3/s. Levine and Meyers (2014) describe the
failure of a 9.7 m wide wooden dam in Odell Creek,
Montana under a flow of 7 m3/s. This failure was
however initiated by bank erosion rather than
breaching of the dam itself. The reported failures
indicate a failure flow of 0.7 to 1 m3/s and meter
dam width. Older dams appear to have a higher fail-
ure flow than new dams.
2 DAM STRUCTURE AND PERFORMANCE
2.1 Wooden dams
Most beaver dams are built from wooden sticks,
with stones at the base. The cross section is triangu-
lar, with an average width-to-height ratio of 2.9,
Watling (2014). The dams have a shallow upstream,
and a steep downstream slope with a sealing layer
made of mud and leaves on the upstream side. A gap
is usually left in the sealing layer to allow for the wa-
ter to flow through the dam.
2.2 Stone dams
When wood is not in sufficient supply, beaver dams
are also built from stones with diameters of up to
300 mm, combined with some wood, e.g. Jung and
Staniforth (2010). The beavers employ a construc-
tion technique where stones and branches are
stacked in layers. The addition of wooden branches
in the rubble dam provides tensile strength, and
thereby increases the stability of these structures
considerably. The beaver’s construction method is
similar to a widespread civil engineering construc-
tion technique called ‘reinforced earth’ or ‘mechani-
cally stabilized earth’.
Fig. 2: Stone dam with wooden reinforcement and props
This technique is employed to create steep em-
bankments e.g. for roads or bridge abutments, with
angles of up to 80 degrees, using alternating layers
of sand and mesh reinforcement. In stone beaver
dams, additional branches are added on the down-
stream side to keep the crown layer of stones in posi-
tion when the dam is overtopped, Fig. 3.
2.3 Current knowledge
The construction techniques of beaver dams are in-
teresting in their own right. They do also open up the
possibility of thinking about nature-based solutions
for small dam structures e.g. to create sustainable
water supplies in seasonal streams in arid regions, to
reduce flood peaks, erosion and incision and to pro-
vide the basis for ecosystem recovery. These solu-
tions would be cheap, since they are non-permanent
structures the planning permission effort would be
reduced, and public acceptance increased. In addi-
tion, these solutions would gradually merge into the
natural environment, eventually becoming part of it.
A better knowledge of construction techniques and
performance seems therefore interesting.
3 EXPERIMENTAL WORK
3.1 Overview
Very little is known about the engineering aspects of
beaver dams. For the assessment of the dams it
would however be useful to have an idea about e.g.
the permeability of a dam, or its stability as a func-
tion of the flow volume. Two series of experiments
were conducted at Southampton University.
3.2 Wood dams
The aim of the first set of tests was to determine the
permeability of typical wooden dam structures. Tests
took place in a trapezoidal channel of 2.5 m width,
0.5 m depth and 50 m length, Fig. 3. The dam had a
height of 0.45 m. the water depths upstream varied
from 0.29 to 0.42 m, with head differences between
0.12 and 0.19 m. A sealing layer made from clay was
attached to the upstream side, leaving only a small
gap to let a flow of 0.031 to 0.129 m3/s pass through.
Fig 3: 0.45 m high wooden dam
The flow volume was measured as a function of
the head difference. It was found that the dam can
best be described as a linear or Darcy filter, with a
filter coefficient of kf = 0.67 m/s, Duckett (2013).
The filter coefficient allows to estimate the flow ve-
locities inside of a beaver dam. Assuming a typical
head difference of 1 m, and a width of 3 m, the flow
velocity inside the dam becomes 0.2 m/s. These low
velocities may allow for small aquatic organisms or
juvenile fish to pass upstream through the dam.
3.3 Stone and stick dams
A second series of tests was conducted at the Uni-
versity of Southampton’s Hydraulics Laboratory us-
ing a smaller flume of 0.30 m width, 0.40 m depth
and 12 m length. The aim of this set of tests was to
assess the stability of rock-and-branches dams, Fig.
4. The dams had a height of 200 mm.
With a scale of approximately 1:7, this corre-
sponds to a typical dam height of 1.4 m. As con-
struction material, pebbles with a diameter of D50 =
30 mm were chosen to model the rounded stones
available in rivers. The dams had an upstream seal-
ing layer made from plastic foil so simulate the char-
acteristics of a beaver dam. A benchmark test was
conducted with a dam built from stones only. It
failed for flow rates of 0.06 m3/s and meter width
(full scale).
a. Dam with internal reinforcement and crown support
b. Plan view with sediment deposition upstream
Fig. 4: Rock-and-branches dam
The insertion of branches as internal reinforce-
ment increased the failure flow to 0.53 m3/s·m,
whilst the addition of props gave a further increase
to 0.88 m3/s·m.
In real dams, sediment is deposited upstream. The
inclusion of a sediment wedge resulted in an even
higher failure flow of 1.34 m3/s·m. This is quite an
impressive performance for a simple structure, and
implies that beaver dams could have been construct-
ed in a large number of rivers.
Observations showed that the props kept the up-
permost stone layer in position when the dam was
overflown. The rock dam’s design was interesting,
and may actually be useful for the ecologically com-
patible construction of small retention dams.
4 DISCUSSION
4.1 Beaver dams in natural rivers
Before human intervention, most smaller rivers in
Eurasia and North America with widths of up to 45
m, and gradients below 0.06, were modified by bea-
vers. This had a profound effect on hydraulics, the
morphology and the ecosystems of rivers. The eco-
systems evolved around the river-and-pond system
created by beavers. Sediment accumulation in the
ponds formed the river valleys. The dynamics of
beaver dams, with dams being destroyed or aban-
doned means that the riverscape was subject to con-
tinuous change. The erosion and incision observed
on many small streams in particular in arid environ-
ments, where steams are seasonal, was prevented by
the dam building activities. It appears that a natural
river system includes, and is transformed by, the ef-
fects of beaver construction. This also means that
larger beaver dams form barriers for fish migration.
Natural rivers were therefore probably not continu-
ous for all aquatic animals.
4.2 Upstream fish passage
Beaver dams with heights of 1 m or more effectively
block the upstream passage of fish during average
flow conditions. Upstream passage is only possible
during high flow situations, where the dam is over-
flown or after failure of the dam. Mitchell and Cun-
jak (2007) considered a 2.5 m high, 30 m long bea-
ver dam in Alaska as the end point of salmon
migration. Bryant (1983) reported that juvenile
salmon were found upstream of a 2.1 m high beaver
dam, indicating that Salmon can pass over beaver
dams under certain flow conditions. Recent work on
beaver dams in Scotland indicates that the fish popu-
lation actually benefits from beaver dams and ponds,
Kemp et al. (2012). Consider that beavers and their
dams have existed in rivers for more than 15 million
years, and that the river ecosystems and species
evolved around them.
4.3 River renaturalisation
In the context of river re-naturalization, these aspects
are now being recognized in the US, see. e.g.
Burchstedt (2013). It is often suggested to use bea-
vers as agents for the re-naturalisation of rivers. Near
human settlements or infrastructure, beaver activities
and their consequences can however have detri-
mental effects such as dam construction in irrigation
or drainage canals, flooding of fields and roads and
the potential danger created by dam failures. In addi-
tion, beavers cannot settle if e.g. the ecosystem is
degraded to an extent that not enough food and water
is available. Artificial beaver dams (ABDs) were
therefore tested by Oregon State University to re-
store a deeply incised seasonal stream, where the
ecosystem was continuously degrading, Nash (2015).
The dams employed here were simple stone and
earth barrages. Nevertheless, the effects of small
dams were profound. The stream changed from
ephemeral to perennial flow, water retention in-
creased, erosion reduced and the vegetation cover re-
established itself and increased. The study demon-
strats the potential value of nature-based solutions in
river management.
4.4 Evolution of river and ecosystems
The role of beaver dams in the evolution of river val-
leys and ecosystems has been discussed in the scien-
tific community since Ruedemann and Schoonmak-
er’s 1938 paper. The most recent consensus appears
to be, that the role of beavers in the formation of riv-
er valleys is significant and stronger than assumed as
yet. This debate, and the extent of beaver popula-
tions and their effects on natural river systems not
affected by human intervention has however not yet
found a mirror in the river engineering community.
On the contrary, it has been ignored and the “natural
state” of a river as defined e.g. in the European Wa-
ter Framework Directive does not even mention bea-
ver dams. This has significant consequences, since
the actual development strategies and implementa-
tion measures as discussed in the following section
are based on the concept of rivers without beavers.
4.5 The European Water Framework Directive
The European Water Framework Directive (WFD) is
a guidance document for the assessment and devel-
opment of all water bodies (rivers, lakes, groundwa-
ter, coastal waters). The ideal development aim
hereby is a ‘good ecological status’, which is defined
as the state of the water body without human inter-
vention. In rivers, one of the main demands is that
for continuity: The best approximation to ecologi-
cal continuum therefore requires consideration of
all hydromorphological mitigation measures that
could reduce any obstacles to migration and im-
prove the quality, quantity and range of habitats af-
fected by the physical alterations. This could include
connectivity to groundwater and to riparian, shore
and intertidal zones. However, the WFD emphasises
migration in particular. Priority should therefore be
given to reducing any obstacles that significantly in-
hibit longitudinal and lateral migration of biota.”,
CISWFD (2003). Unfortunately, beaver dams as in-
tegral components of a natural river systems within
the constraints mentioned in section 2, are not even
mentioned in the WFD. The possibility of biologi-
cally created alterations of the river, which affect
continuity for organisms and sediment profoundly, is
therefore not part of the perceived ‘natural state’ of a
river. Beaver dams also affect water retention, mor-
phodynamics and river valley formation. This opens
an important question, namely does the WFD’s de-
mand for complete longitudinal continuity and its
consequences, such as removal of weirs, really lead
to more natural rivers? Or is a new definition of the
‘natural state’ of rivers required?
4.6 Nature based solutions for stream restoration
and hydro-meteorological risk reduction
The construction methods employed by beavers may
allow to develop simple, nature based solutions for
small dams in the upper reaches of small streams. In
many semi-arid regions such as the Mediterranean
regions, the ecosystems around such streams are de-
graded to such an extent that they cannot recover
even if left alone. This is mainly caused by the lack
of water supply. Rain water runs off directly, eroding
the streams in the process. Flood peaks tend to be
high since there is only little retention. The construc-
tion of dams based on beaver technology would
mean that a nature based solution could be devel-
oped. The experiments conducted so far have given
the initial information regarding construction tech-
nique, and failure loads. Small dams would be cheap
and easy to construct. The materials used are local.
The ponds serve to recharge the groundwater, pro-
vide a sustainable water supply, and to provide re-
tention zones to reduce flood peaks.
4.7 Outlook
The knowledge about the beaver dam’s engineering
characteristics is still limited. Their effects on sedi-
ment transport and river valley formation requires
further work. The stability and construction methods
employed, and the ecological characteristics such as
the passability for aquatic organisms need to be in-
vestigated. To create a development framework for
small rivers, a new definition of what constitutes a
natural river, including beaver dams, has to be
found. It has already been discussed that the interests
of beavers and humans are not necessarily compati-
ble. Technical solutions i.e. artificial beaver dams
with characteristics similar to actual dams (height,
length, permeability) - need to be developed. River
renaturalisation concepts which include the effects
of beaver dams, and possibly even taking their tem-
poral dynamics into account could be envisaged. Fi-
nally, the possibilities and potential of nature based
solutions for ecosystem redevelopment could be ex-
plored.
5 CONCLUSIONS
The engineering characteristics of beaver dams were
investigated using a literature study, and hydraulic
model tests. The following conclusions are drawn:
With lengths of up to 850 m, beaver dams resem-
ble engineered structures.
Dam heights can reach 5.3 m, although heights of
up to 1.5 m are typical.
Their effect on river hydraulics, sediment
transport, groundwater retention and flood peak
reduction is profound.
Stone dams employ a reinforced earth construc-
tion technology which results in significantly en-
hanced strength.
Failure flows were determined as 0.8 m3/s per me-
ter width for a 1.4 m high dam without sediment
deposition (i.e. just after construction).
Failure flows for dams with upstream sediment
deposition reached 1.34 m3/s and meter width.
The construction methods employed by beavers
may provide a basis for nature-based solutions for
river restoration, water retention and flood peak
reduction.
The role of beaver dams as integral components of
natural rivers needs further discussion.
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... Such materials can be mud, turf, bones of large mammals and stones. Some descriptions of dams report the dominance of stones [64][65][66] and dams in which mammoth bones were used as the building material [67]. During the studies carried out in the Tuchola Forest, single stones were found in Holocene reservoir sediments. ...
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Beavers have lived in the territory of Poland since the beginning of the Holocene, as testified by bone remains found in archaeological sites of different ages. The area inhabited by these animals has experienced continuing transformations of terrain relief, geological structure, hydrology and plant cover. In Poland, beavers are partially protected and their population has spread in virtually every part of the country (except in the highest mountain ranges). The authors of this paper wish to present the results of field works carried out since 2006 in the Tuchola Forest (Polish Plain). This paper aims to identify the potential sediments of relict beaver ponds and their sedimentological features. The studies are also backed up with a description of radiocarbon dating of samples. The results indicate that beavers used to live in the Tuchola Forest in the Middle Ages, as shown by the radiocarbon dates and sequences of mineral–organic deposits found in exposures and geological boreholes. The spatial distribution of organic and mineral deposits in wider sections of river valleys can be explained by the avulsion of the riverbed downstream of the pond and by the distribution of ponds in the Gołyjonka valley. The discovery of relict beaver pond sediments suggests that the activity of these mammals in the Middle Ages played a major part in shaping the landscape of the valley. The results of studies clearly indicate that analyses of the valley sediment facies of small watercourses should take into account the role beavers played in the past in shaping the landscape of the analysed valley. This highlights the insufficiency of studies concerning the activity of beavers in river valleys.
... Such materials can be mud, turf, bones of large mammals and stones. Some descriptions of dams report the dominance of stones [64][65][66] and dams in which mammoth bones were used as the building material [67]. During the studies carried out in the Tuchola Forest, single stones were found in Holocene reservoir sediments. ...
... The internal structure of beaver dams is very complex. Beavers build dams using various materials, e.g., wood, sediments, grass, leaves and stones [64][65][66]. Generally, beavers use anything that is available near their habitat. ...
Article
Beavers have lived in the territory of Poland since the beginning of the Holocene, as testified by bone remains found in archaeological sites of different ages. The area inhabited by these animals has experienced continuing transformations of terrain relief, geological structure, hydrol-ogy and plant cover. In Poland, beavers are partially protected and their population has spread in virtually every part of the country (except in the highest mountain ranges). The authors of this paper wish to present the results of field works carried out since 2006 in the Tuchola Forest (Polish Plain). This paper aims to identify the potential sediments of relict beaver ponds and their sedimentological features. The studies are also backed up with a description of radiocarbon dating of samples. The results indicate that beavers used to live in the Tuchola Forest in the Middle Ages, as shown by the radiocarbon dates and sequences of mineral-organic deposits found in exposures and geological boreholes. The spatial distribution of organic and mineral deposits in wider sections of river valleys can be explained by the avulsion of the riverbed downstream of the pond and by the distribution of ponds in the Gołyjonka valley. The discovery of relict beaver pond sediments suggests that the activity of these mammals in the Middle Ages played a major part in shaping the landscape of the valley. The results of studies clearly indicate that analyses of the valley sediment facies of small watercourses should take into account the role beavers played in the past in shaping the landscape of the analysed valley. This highlights the insufficiency of studies concerning the activity of beavers in river valleys.
... Ensuite, les principaux impacts négatifs sur la migration du saumon sont associés à l'effet de barrière migratoire potentielle qui limite la distribution amont des salmonidés vers les zones de fraie (Mitchell et Cunjak, 2007dans Kemp et al., 2012 ainsi que le blocage complet de la migration lors des périodes d'étiage (Pollock et al., 2017). Par conséquent, l'ampleur de ces impacts est (Stout et al., 2016;Muller et Watling, 2016), de l'intensité des réajustements du cours d'eau et de la variation des conditions hydrologiques (Butler et al., 2005). Enfin, l'association entre la présence de barrages de castor à la problématique de restriction du passage du poisson peut parfois être précipitée et spéculative (Kemp et al., 2012). ...
Technical Report
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... In contrast to these species, beavers, as generalist herbivores, do not solely rely on diving for food acquisition (Haarberg & Rosell, 2006 (Harrington et al., 2012). Beavers may also have dived less due to (i) the lower availability of aquatic plants in river habitats (Milligan & Humphries, 2010), (ii) the fact that they do not build dams in our study area, a behavior that necessitates diving to seal their dams with mud and stones (Müller & Watling, 2016), and (iii) the lack of data collection during winter (December-March), where the partly ice-covered rivers may force beavers to dive. Local habitat features and differences in the (seasonal) availability of food resources may thus impact diving behavior in beavers; for example, in pond habitats, beaver diets have been found to contain higher percentages of aquatic vegetation, in particular, during autumn/winter (Milligan & Humphries, 2010). ...
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Semi-aquatic mammals have secondarily returned to the aquatic environment, although they spend a major part of their life operating in air. Moving both on land, as well as in, and under water is challenging because such species are considered to be imperfectly adapted to both environments. We deployed accelerometers combined with a depth sensor to study the diving behavior of 12 free-living Eurasian beavers Castor fiber in southeast Norway between 2009 and 2011 to examine the extent to which beavers conformed with mass-dependent dive capacities, expecting them to be poorer than wholly aquatic species. Dives were generally shallow (<1 m) and of short duration (<30 s), suggesting that the majority of dives were aerobic. Dive parameters such as maximum diving depth, dive duration, and bottom phase duration were related to the effort during different dive phases and the maximum depth reached. During the descent, mean vectorial dynamic body acceleration (VeDBA—a proxy for movement power) was highest near the surface, probably due to increased upthrust linked to fur- and lung-associated air. Inconsistently though, mean VeDBA underwater was highest during the ascent when this air would be expected to help drive the animals back to the surface. Higher movement costs during ascents may arise from transporting materials up, the air bubbling out of the fur, and/or the animals’ exhaling during the bottom phase of the dive. In a manner similar to other homeotherms, beavers extended both dive and bottom phase durations with diving depth. Deeper dives tended to have a longer bottom phase, although its duration was shortened with increased VeDBA during the bottom phase. Water temperature did not affect diving behavior. Overall, the beavers’ dive profile (depth, duration) was similar to other semi-aquatic freshwater divers. However, beavers dived for only 2.8% of their active time, presumably because they do not rely on diving for food acquisition.
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Biohybrid robotics takes an engineering approach to the expansion and exploitation of biological behaviors for application to automated tasks. Here we identify the construction of living buildings and infrastructure as a high-potential application domain for biohybrid robotics, and review technological advances relevant to its future development. Construction, civil infrastructure maintenance, and building occupancy in the last decades have comprised a major portion of economic production, energy consumption, and carbon emissions. Integrating biological organisms into automated construction tasks and permanent building components therefore has high potential for impact. Live materials can provide several advantages over standard synthetic construction materials, including self-repair of damage, increase rather than degradation of structural performance over time, resilience to corrosive environments, support of biodiversity, and mitigation of urban heat islands. Here we review relevant technologies, which are currently disparate. They span robotics, self-organizing systems, artificial life, construction automation, structural engineering, architecture, bioengineering, biomaterials, and molecular and cellular biology. In these disciplines, developments relevant to biohybrid construction and living buildings are in early stages, and typically are not exchanged between disciplines. We therefore consider this review useful to the future development of biohybrid engineering for this highly interdisciplinary application.
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The billion-dollar river restoration industry relies primarily on the concept of a free-flowing river to set restoration targets. However, rivers include natural barriers such as beaver dams, wood jams, glacial deposits, and bedrock constrictions. Following European colonization, most of these barriers were removed; some were replaced with far more homogenous ones such as human dams and road crossings. Although the biota intended to benefit from restoration evolved in rivers with natural barriers in place, little is known about the functions of the barriers that have been lost. Beaver dams—the subject of this dissertation—are just one type of the many natural barriers that should be considered by river restoration efforts. Chapter 2 presents a conceptual model of a river network that includes barriers, generating the fundamental hypothesis that intact and failed barriers create patchy features that store and release water and sediment. In chapter 3, a detailed geomorphic comparison of free-flowing and impounded channels shows that beaver dams decouple stream reaches, where distinct differences in adjacent channel reaches are explained by the presence of beaver dams. Observations of fine sediment deposits in steep reaches downstream of dams and of net sediment losses from old ponds support the hypothesis that beaver ponds store and release sediment. The hydrologic study of chapter 4 shows that the river channel through a beaver meadow loses water during rain events and subsequently gains water during recession, confirming the hypothesis of storage and release of water. Additional water gains during storm recessions in excess of the volume lost during the events, along with significantly lower runoff rates in the meadow channel during the events, suggest additional storage and subsequent release of upland runoff by the meadow. Chapter 5 examines summer water temperature at the streambed, which further demonstrates the patchiness generated by the intact and failed beaver dams. A distinct cold pool exists at a scour hole generated by a dam failure, and beaver dams buffer water temperatures upstream. As chapter 6 concludes, this patchiness should be further researched as a target for river restoration efforts where natural dams cannot be directly restored.
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Beaver ponds and beaver-impounded vegetation are indicators of past or present beaver activity that can be detected from aerial photography. A method to quantitatively relate these beaver works with the density of active beaver colonies could benefit beaver management, particularly in areas lacking beaver population data. We compared historical maps (1961–2006) of beaver works at Voyageurs National Park, Minnesota, USA with concurrent aerial surveys of beaver colonies. We tested 2 landscape-scale models of beaver colony density previously developed for a period of beaver population expansion (1940–1986), but they failed to predict colony density after 1986, a period of declining beaver population. We developed a new landscape-scale regression, calculating that 2.15% of the landscape would be flooded by every 100 additional beaver colonies (R2 = 0.53, P = 0.027). Classification tree analysis of individual pond sites showed that open water pond and impounded marsh area were the primary predictors of beaver colony presence or absence, but that the classification trees were far better at identifying inactive sites (>93% correct) than active sites (35–38% correct). The area of open water in beaver ponds is a good but not perfect indicator of beaver activity that can be used by wildlife managers as a landscape-scale indicator of beaver colony density. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
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Biogenic features such as beaver dams, large wood, and live vegetation are essential to the maintenance of complex stream ecosystems, but these features are largely absent from models of how streams change over time. Many streams have incised because of changing climate or land-use practices. Because incised streams provide limited benefits to biota, they are a common focus of restoration efforts. Contemporary models of long-term change in streams are focused primarily on physical characteristics, and most restoration efforts are also focused on manipulating physical rather than ecological processes. We present an alternative view, that stream restoration is an ecosystem process, and suggest that the recovery of incised streams is largely dependent on the interaction of biogenic structures with physical fluvial processes. In particular, we propose that live vegetation and beaver dams or beaver dam analogues can substantially accelerate the recovery of incised streams and can help create and maintain complex fluvial ecosystems.
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broad alluvial valley during the summers of 2002-2005. We studied a 1.5 km reach of the fourth-order Colorado River in Rocky Mountain National Park (RMNP), Colorado, USA. The beaver dams and ponds greatly enhanced the depth, extent, and duration of inundation associated with floods; they also elevate the water table during both high and low flows. Unlike previous studies we found the main effects of beaver on hydrologic processes occurred downstream of the dam rather than being confined to the near-pond area. Beaver dams on the Colorado River caused river water to move around them as surface runoff and groundwater seepage during both high- and low-flow periods. The beaver dams attenuated the expected water table decline in the drier summer months for 9 and 12 ha of the 58 ha study area. Thus we provide empirical evidence that beaver can influence hydrologic processes during the peak flow and low-flow periods on some streams, suggesting that beaver can create and maintain hydrologic regimes suitable for the formation and persistence of wetlands.
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North American Beavers (Castor canadensis) are remarkable for their ability to build dams and modify their habitat. Dams are typically made of the boles and branches of trees and large shrubs, and reinforced with mud and rocks. Here, we report two unusual Beaver dams in centralYukon, Canada, that are made primarily of medium-sized rocks. This observation points to the adaptability of Beavers in using available materials to build their dams.
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Reintroduction of beaver (Castor spp) may facilitate rehabilitation of freshwater habitats providing a cost-effective sustainable means of improving ecological conditions. Despite extensive research, debate and consultation, a general consensus on the impact of beaver on fishes has proven elusive because of variability in biological response. This paper provides a systematic review of the impacts of beaver dams on fishes and fish habitat based on a meta-analysis of the literature and expert opinion. Research is regionally biased to North America (88%). The most frequently cited benefits of beaver dams were increased habitat heterogeneity, rearing and overwintering habitat and flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119). Impacts were spatially and temporally variable and differed with species. The majority of 49 North American and European experts considered beaver to have an overall positive impact on fish populations, through their influence on abundance and productivity. Perceived negative effects related to the movement of aquatic organisms in tributary streams, including upstream and downstream migrating salmonids, and the availability of suitable spawning habitat.
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Beaver dams in streams are generally considered to increase bed elevation through in-channel sediment storage, thus, reintroductions of beaver are increasingly employed as a restoration tool to repair incised stream channels. Here we consider hydrologic and geomorphic characteristics of the study stream in relation to in-channel sediment storage promoted by beaver dams. We also document the persistence of sediment in the channel following breaching of dams. Nine reaches, containing 46 cross-sections, were investigated on Odell Creek at Red Rock Lakes National Wildlife Refuge, Centennial Valley, Montana. Odell Creek has a snowmelt-dominated hydrograph and peak flows between 2 and 10 m3 s− 1. Odell Creek flows down a fluvial fan with a decreasing gradient (0.018–0.004), but is confined between terraces along most of its length, and displays a mostly single-thread, variably sinuous channel. The study reaches represent the overall downstream decrease in gradient and sediment size, and include three stages of beaver damming: (1) active; (2) built and breached in the last decade; and (3) undammed. In-channel sediment characteristics and storage were investigated using pebble counts, fine-sediment depth measurements, sediment mapping and surveys of dam breaches. Upstream of dams, deposition of fine (≤ 2 mm) sediment is promoted by reduced water surface slope, shear stress and velocity, with volumes ranging from 48 to 182 m3. High flows, however, can readily transport suspended sediment over active dams. Variations in bed-sediment texture and channel morphology associated with active dams create substantial discontinuities in downstream trends and add to overall channel heterogeneity. Observations of abandoned dam sites and dam breaches revealed that most sediment stored above beaver dams is quickly evacuated following a breach. Nonetheless, dam remnants trap some sediment, promote meandering and facilitate floodplain development. Persistence of beaver dam sediment within the main channel on Odell Creek is limited by frequent breaching (< 1–5 years), so in-channel sediment storage because of damming has not caused measurable channel aggradation over the study period. Enhanced overbank flow by dams, however, likely increases fine-grained floodplain sedimentation and riparian habitat. Contrasts between beaver-damming impacts on Odell Creek and other stream systems of different scales suggest a high sensitivity to hydrologic, geomorphic, and environmental controls, complicating predictions of the longer-term effects of beaver restoration.
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page 439 Abstract The Eurasian and North American beavers are similar in their ecological requirements, and require water deep enough to cover the entrance to their lodge or burrow. A food cache is often built next to the lodge or burrow, except in some southern areas. On small streams (up to fourth order) dams are frequently built to create an impoundment, generally on low gradient streams, although at high population densities dams may be built on steeper gradient streams. On large rivers or in lakes, simply a lodge with its food cache may be built. The beaver is a keystone riparian species in that the landscape can be considerably altered by its activities and a new ecosystem created. The stream above a dam changes from lotic to lentic conditions. There are hydrological, temperature and chemical changes, depending on types of dams and locations. Although the invertebrates may be fewer per unit area, total number of organisms increases, and diversity increases as the pond ages. In cool, small order streams, the impoundments provide better habitat for large trout, possibly creating angling opportunities. However, at sites