Beaver damming

1 WHY DO BEAVERS BUILD DAMS?

Beavers are semi-aquatic animals and feel safest in deep water, which allows them to move freely through their territory and escape predators. Beavers also like the entrance to their lodge or burrow to be submerged, so if they live in an area with fluctuating water levels, they’ll build a dam to create a deep pond. Dams are not usually found in large rivers and streams, as the water depth is sufficient.

2 HOW ARE WATER LEVELS MAINTAINED?

The depth of the pond is determined by the height of the dam, known as the ‘crest level’. The sound of water trickling over the lowest point of the crest level alerts the beavers to where the barrier needs to be patched and raised. Patching raises the water level slightly, pushing the water over the next lowest spot, which is then also patched – and on it goes. Over time, beaver dams grow in length and height and can develop into enormous structures in some cases. Both males and females build, assisted by their kits, who instinctively know what to do.

3 CAN BEAVERS DAM FAST-FLOWING WATER?

When they do dam a fast-flowing stream, beavers build out from the banks with sticks placed parallel to the flow, rather than perpendicular to it. The channel is slowly confined into a smaller and smaller space until the beavers can eventually block the gap. Dams are built with whatever can be found locally – willow branches and hazel coppiced out of hedges are particularly popular on Devon’s River Otter. Beavers also fell and chop up small trees using their teeth, and even use debris such as bricks, lumps of concrete and fence posts.