Misplaced Pages

#808191

39-461: A beaver dam is a structure built by beavers. Beaver Dam or Beaverdam may also refer to: Beaver dam A minimum water level of 0.6 to 0.9 metres (2.0 to 3.0 ft) is required to keep the underwater entrance to beaver lodges from being blocked by ice during the winter. In lakes, rivers and large streams with deep enough water, beavers may not build dams, and live in bank burrows and lodges. Beavers start construction by diverting

78-418: A freeboard above the water level. When heavy rains occur, the river or lake fills up. Afterward the dam gradually releases the extra stored water, thus somewhat reducing the height of the flood wave moving down the river. The surface of any stream intersects the surrounding water table. By raising the stream level, the gradient of the surface of the water table above the beaver dam is reduced, and water near

117-520: A polymer of β-glucose monomers . (This creates a more crystalline structure than is found in starch , which is composed of α-glucose monomers. Cellulose is a type of polysaccharide .) Many bacteria produce cellulase which can split off the glucose and use it for energy. Just as algae receive energy from sunlight, these bacteria derive energy from cellulose, and form the base of a very similar food chain. Additionally, bacterial populations absorb nitrogen and phosphorus compounds as they pass by in

156-570: A deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in this aquifer may rise to a level that is greater or less than the elevation of the actual water table. The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface , not the water table. The water table may vary due to seasonal changes such as precipitation and evapotranspiration . In undeveloped regions with permeable soils that receive sufficient amounts of precipitation,

195-496: A problem to Earth's ecology as carbon dioxide production. Studies have shown that beaver dams along a stream contribute to denitrification (the conversion of nitrogen compounds back into nitrogen). Bacteria in the dirt and the plant debris, which collects at the dams, turns nitrates into nitrogen gas. The gas bubbles to the surface and mixes with the atmosphere once more. Beaver dams and the associated ponds can provide nurseries for salmon and trout . An early indication of this

234-621: A remarkable comeback in the United States (after near extirpation in the nineteenth century) and are likely to continually recolonize suitable habitat. Modern solutions include relatively cost-effective and low maintenance flow devices . Introduced to an area without its natural predators, as in Tierra del Fuego , beavers have flooded thousands of acres of land and are considered a plague. One notable difference in Tierra del Fuego from most of North America

273-400: Is 775 metres (2,543 ft) long. Satellite photos provided by NASA WorldWind show the dam did not exist in 1975, but it appeared in subsequent images. It has two or more lodges and is a combination of two original dams. Google Earth images show new dams being built which could ultimately join the main dam and increase the overall length by another 50 to 100 metres (160 to 330 ft) during

312-457: Is equal to the atmospheric pressure (where gauge pressure = 0). It may be visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity. The groundwater may be from precipitation or from groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths, water fills in more of

351-411: Is groundwater that has remained in an aquifer for several millennia and occurs mainly in deserts . It is non-renewable by present-day rainfall due to its depth below the surface, and any extraction causes a permanent change in the water table in such regions. Most crops need a water table at a minimum depth. For some important food and fiber crops a classification was made because at shallower depths

390-577: Is that the trees in Tierra del Fuego cannot be coppiced as can willows, poplars, aspens, and other North American trees. Thus the damage by the beavers seems more severe. The beaver's disruption is not limited to human geography; beavers can destroy nesting habitat for endangered species. Warming temperatures in the Arctic allow beavers to extend their habitat further north, where their dams impair boat travel, impact access to food, affect water quality, and endanger downstream fish populations. Pools formed by

429-461: The water table in wetlands such as peatlands , they can stabilize a fluctuating water table, which influences the levels of both carbon and water. In a 2017 study of beaver dam hydrology, monitored beaver dams in a Rocky Mountain peatland were found to increase groundwater storage and regional water balance , which can be beneficial for preventing drought. The study also suggested potential to improve carbon sequestration . Beaver ponds can cause

SECTION 10

#1732851140809

468-443: The aquifer and the permeability of the material. The water table does not always mimic the topography due to variations in the underlying geological structure (e.g., folded, faulted, fractured bedrock). A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table. This occurs when there is an impermeable layer of rock or sediment ( aquiclude ) or relatively impermeable layer ( aquitard ) above

507-475: The beaver dam flows more slowly into the stream. This may also help in reducing flood waves, and increasing water flow when there is no rain. In other words, beaver dams smooth out water flow by increasing the area wetted by the stream. This allows more water to seep into the ground where its flow is slowed. This water eventually finds its way back to the stream. Rivers with beaver dams in their head waters have lower high water and higher low water levels. By raising

546-551: The bottom widens. Research is sparse, but it seems likely that parts of the bottomland in North America was created, or at least added to, by the efforts of the generations of beavers that lived there. Humans sometimes build structures similar to beaver dams in streams, either to get the benefits of beaver dams in places without beavers, or to encourage beavers to settle in a particular area. These are often called "beaver dam analogs" (BDA) although other names are also used. When

585-402: The breakdown of toxins such as pesticides and the retention of silt by beaver dams. Beaver dams reduce erosion and decrease the turbidity that can be a limiting factor for some aquatic life. The benefits may be long-term and largely unnoticed unless a catchment is monitored closely. Almost half of endangered and threatened species in North America rely upon wetlands. In 2012, a systematic review

624-418: The capillary effect ( capillary fringe ) in soils , sediments and other porous media . In the aquifer, groundwater flows from points of higher pressure to points of lower pressure, and the direction of groundwater flow typically has both a horizontal and a vertical component. The slope of the water table is known as the “hydraulic gradient”, which depends on the rate at which water is added to and removed from

663-459: The crop suffers a yield decline. A water table close to the surface affects excavation, drainage, foundations, wells and leach fields (in areas without municipal water and sanitation), and more. When excavation occurs near enough to the water table to reach its capillary action, groundwater must be removed during construction. This is conspicuous in Berlin , which is built on sandy, marshy ground, and

702-599: The dam has flooded enough area to the proper depth to form a protective moat for the lodge (often covering many acres), beavers begin construction of the lodge. Trees approaching a diameter of 90 centimetres (3.0 ft) may be used to construct a dam, although the average is 10 to 30 centimetres (3.9 to 11.8 in). Log length depends on the diameter of the tree and the size of the beaver. There are recorded cases of beavers felling trees of 45 metres (148 ft) tall and 115 centimetres (45 in) in diameter. Logs of this size are not intended to be used as structural members of

741-418: The dam. Water table The water table is the upper surface of the zone of saturation . The zone of saturation is where the pores and fractures of the ground are saturated with groundwater , which may be fresh, saline, or brackish, depending on the locality. It can also be simply explained as the depth below which the ground is saturated. The water table is the surface where the water pressure head

780-530: The dam; rather, the bark is used for food, and sometimes to get to upper branches. It takes a beaver about 20 minutes to cut down a 15-centimetre (5.9 in) wide aspen, by gnawing a groove around the trunk in an hourglass shape. A beaver's jaws are powerful enough to cut a 1.5-centimetre (0.59 in) sapling in one bite. Maintenance work on the dam and lodges is often done in autumn. If beavers are considered central place foragers , their canals may be considered an extension of their "central place" far beyond

819-406: The dams store heat, thus changing local hydrology and causing localized thawing of permafrost that in turn contributes to global warming. If a beaver pond becomes too shallow due to sediment accumulation, or the tree supply is depleted, beavers will abandon the site. Eventually the dam will be breached and the water will drain out. The rich thick layer of silt, branches, and dead leaves behind

SECTION 20

#1732851140809

858-404: The factors associated with the decline of salmon runs were extant at that time. There are several reasons why beaver dams increase salmon runs. They produce ponds that are deep enough for juvenile salmon to hide from predatory wading birds . They trap nutrients in their ecology and notably the nutrient pulse represented by the migration of the adult salmon upstream. These nutrients help feed

897-412: The flooding occurs next to a railroad roadbed, it can cause derailments by washing out the tracks. When a beaver dam bursts , the resulting flash flood may overwhelm a culvert . Traditional solutions to beaver problems have been focused on the trapping and removal of all the beavers in the area. While this is sometimes necessary, it is typically a short-lived solution, as beaver populations have made

936-487: The goal is to attract beavers, sometimes the site is unsuitable in its present condition, such as being too eroded for beavers to build a dam in their usual way. BDA builders may use construction techniques beyond the beaver's capabilities, such as driving wooden posts into the stream bed to brace horizontal branches that would otherwise be washed away. The hope is that beavers who wander by or are brought in will choose to live there and take over construction and maintenance of

975-406: The growth of adventitious roots. Finally the meadow will be colonized by riverine trees, typically aspens, willows and such species which are favoured by the beaver. Beavers are then likely to recolonize the area, and the cycle begins again. Each time the stream life cycle repeats itself another layer of organic soil is added to the bottom of the valley. The valley slowly fills and the flat area at

1014-444: The growth of species of plants that are critical to populations of songbirds in decline, beaver dams help create food and habitat. The presence of beaver dams has been shown to be associated with an increased diversity of songbirds. They can also have positive effects on local waterfowl, such as ducks, that are in need of standing water habitats. Beaver dams can be disruptive; the flooding can cause extensive property damage, and, when

1053-864: The juveniles after the yolk sac has been digested. The dams provide calm water which means that the young salmon can use energy for growth rather than for navigating currents; larger smolts with a food reserve have a better rate of survival when they reach the sea. Finally, beaver dams keep the water clear which favours all salmonoids . Beaver dams have been shown to be beneficial to frog and toad populations, likely because they provide protected areas for larvae to mature in warmer, well-oxygenated water. A study in Alberta, Canada, showed that "Pitfall traps on beaver ponds captured 5.7 times more newly metamorphosed wood frogs, 29 times more western toads and 24 times more boreal chorus frogs than on nearby free-flowing streams." Beaver dams help migrating songbirds . By stimulating

1092-535: The lodge, according to a 2004–2012 study that mapped beaver ponds and cut stumps. Some people consider that by building dams beavers are expressing tool use behaviour. Beaver dams typically range in length from a few meters to about 100 metres (330 ft). Canals can be over 0.5 kilometres (1,600 ft) long. The largest known beaver dam is in Wood Buffalo National Park in Alberta , Canada, and

1131-435: The main water table/aquifer but below the land surface. If a perched aquifer's flow intersects the surface, at a valley wall, for example, the water is discharged as a spring . On low-lying oceanic islands with porous soil, freshwater tends to collect in lenticular pools on top of the denser seawater intruding from the sides of the islands. Such an island's freshwater lens, and thus the water table, rises and falls with

1170-567: The next decade. Coordinates: 58°16′15″N 112°15′6″W  /  58.27083°N 112.25167°W  / 58.27083; -112.25167 . Another large beaver dam measuring 2,139 feet (650 m) long, 14 feet (4.3 m) high and 23 feet (7.0 m) thick at the base was found in Three Forks, Montana . Dam building can help to restore damaged wetlands. Wetland benefits include flood control downstream, biodiversity (by providing habitat for different species), and water cleansing, both by

1209-453: The old dam is an ideal habitat for some wetland species. As the wetland fills up with plant debris and dries out, pasture species colonize it and the wetland may eventually become a meadow suitable for grazing in a previously forested area. This provides a valuable niche for many animals which otherwise would be excluded. Beaver dam creation also increases the plants the dams were made from (such as willows) to reproduce by cutting , encouraging

Beaver dam (disambiguation) - Misplaced Pages Continue

1248-404: The pore spaces in the soils, until a zone of saturation is reached. Below the water table, in the phreatic zone (zone of saturation), layers of permeable rock that yield groundwater are called aquifers . In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define. “Water table” and “ water level ” are not synonymous. If

1287-400: The removal of nutrients from the stream flow. Farming along the banks of rivers often increases the loads of phosphates, nitrates and other nutrients, which can cause eutrophication and may contaminate drinking water. Besides silt, the beaver dam collects twigs and branches from the beavers' activity as well as leaves, notably in the autumn . The main component of this material is cellulose ,

1326-426: The stream to lessen the water's flow pressure. Branches and logs are then driven into the mud of the stream bed to form a base. Then sticks, bark (from deciduous trees), rocks, mud, grass, leaves, masses of plants, and anything else available are used to build the superstructure. Beavers can transport their own weight in material; they drag logs along mudslides and float them through canals to get them in place. Once

1365-479: The tides. In some regions, for example, Great Britain or California , winter precipitation is often higher than summer precipitation and so the groundwater storage is not fully recharged in summer. Consequently, the water table is lower during the summer. This disparity between the level of the winter and summer water table is known as the "zone of intermittent saturation", wherein the water table will fluctuate in response to climatic conditions. Fossil water

1404-457: The water stream and keep these and other nutrients in the beaver pond and the surrounding ecology. Agriculture introduces herbicides and pesticides into streams. Some of these toxicants are metabolized and decomposed by the bacteria in the cellulose-rich bottom of a beaver dam. Some scientists believe that the nitrogen cascade , the production of more fixed nitrogen than the natural cycles can turn back into nitrogen gas, may be as much of

1443-409: The water table typically slopes toward rivers that act to drain the groundwater away and release the pressure in the aquifer. Springs , rivers , lakes and oases occur when the water table reaches the surface. Groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies. Within an aquifer, the water table is rarely horizontal, but reflects the surface relief due to

1482-499: Was conducted on the impacts of beaver dams on fishes and fish habitat (biased to North America (88%)). The most frequently cited benefits of beaver dams were increased habitat heterogeneity , rearing and overwintering habitat, 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). A beaver dam may have

1521-511: Was seen following the 1818 agreement between the British government of Canada and the government of America allowing Americans access to the Columbia watershed. The Hudson's Bay Company , in a fit of pique, instructed its trappers to extirpate the fur-bearing animals in the area. The beaver was the first to be made locally extinct. Salmon runs fell precipitously in the following years, even though none of

#808191