Beaver Dam Traditional Cache

The Beaver Dam is no longer across the trail from the cache. I moved it to the dam side, after many complaints about a big water snake near the cache site.

Beaver dams are dams built by beavers to provide ponds as protection against predators such as coyotes, wolves, and bears, and to provide easy access to food during winter. These structures modify the natural environment in such a way that the overall ecosystem builds upon the change, making beavers a keystone species. Beavers work at night and are prolific builders, carrying mud and stones with their fore-paws and timber between their teeth. Beavers can rebuild primary dams overnight, though they may not defend secondary dams as vigorously.

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 instead live in bank burrows and lodges. If the water is not deep enough to keep beavers safe from predators and their lodge entrances ice-free, beavers build dams.

Beavers start construction by diverting 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. The average height of a dam is about 1.8 metres (5.9 ft) with an average depth of water behind the dam of 1.2 to 1.8 m. The thickness of the dam is often around 1 m or more. The length depends on the stream width, but averages about 4.5 m long.

Beavers vary the type of dam built and how they build it, according to the speed of water on the stream. In slow-moving water, they build a straight dam, whereas in fast-moving water they tend to be curved. Spillways and passageways are built into the dam to allow excess water to drain off without damaging it. Dams are generally built wider at the base and the top is usually tilted upstream to resist the force of the current. Beavers can transport their own weight in material; they drag logs along mudslides and float them through canals to get them in place. Once 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 on 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 cm. The length depends on the diameter of the tree and the size of the beaver. There are recorded cases of beavers felling logs of as much 45 m tall and 115 cm in diameter. Logs of this size are not intended to be used as structural members of the dam, but rather the bark is used for food, and sometimes to get at upper branches. It takes a beaver about 20 minutes to cut down a 15 cm wide aspen, by gnawing a groove around the trunk in an hourglass shape. A beaver's jaws are so powerful they can cut a 1.5 cm sapling in one bite.

Maintenance work on the dam and lodges is particularly heavy in autumn.

Beaver dams can be disruptive; the flooding can cause extensive property damage, and when the flooding occurs next to a railroad roadbed, it can cause derailments by washing out the tracks, or when a beaver dam bursts and the resulting flash flood overwhelms a culvert. 

Dam building can be very beneficial in restoring wetlands. Such wetland benefits include flood control downstream, biodiversity (by providing habitat for many rare as well as common species), and water cleansing, both by the breakdown of toxins such as pesticides and the retention of silt by beaver dams. 

A beaver dam has a certain amount of freeboard above the water level. When heavy rains occur, the river or lake fills up and the dam gradually releases the extra stored water. Often this is all that is necessary to reduce the height of the flood wave moving down the river, and will reduce or eliminate damage to human structures.

Beaver ponds can cause 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 eutrofication and may contaminate drinking water.

Agriculture also 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.

Beaver dams and the associated ponds can provide nurseries for salmon and trout.

Beaver dams have been shown to be beneficial to frog and toad populations, likely because they provide protected areas for larvae to mature in warm, well-oxygenated water. 

Beaver dams help migrating songbirds. By stimulating the growth of species of plants that are critical to populations of songbirds in decline, beaver dams help create food and habitat for populations of songbirds in decline. The presence of beaver dams has been shown to be associated with an increased diversity of songbirds.

If a beaver pond becomes too shallow due to sediment accumulation, or if 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 the old dam is the ideal habitat for wetland species. Many may have been on the fringes of the pond. Wetlands have significant environmental benefits.

As the wetland fills up with plant debris and dries out, pasture species colonize it and the wetland becomes a meadow suitable for grazing in an area with nothing but forest down to the stream edge. This provides a valuable niche for many animals which otherwise would be excluded.

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 rich organic soil is added to the bottom of the valley. The valley slowly fills and the flat area at the bottom gets wider. Research is sparse, but it seems likely that much of the fabled bottom land in North America was created, or at least added to, by the efforts of the generations of beavers that lived there.

The cache is a "small", camoed pill bottle. It is tied in. It holds a log in a plastic zip lock bag. Please BYOP and put things back as you found them, including the camo.