Artificial Beaver Dams for Sustainable Water Management and Restoration of Small Streams

In Eurasia and North America, beaver dams were integral parts of natural smaller river systems for more than 15 million years. Their existence modifies rivers dramatically, reducing the gradient, flow velocity and erosive tendencies, accumulating sediment, and increasing water storage and ground water levels. Beavers are termed ‘ecosystem engineers’ since they create new ecosystems, which without them would not exist.

With the near extinction of beavers several hundred years ago, their role in natural river systems has largely been forgotten, and their effects have disappeared. Today, there are many small streams and rivers which suffer from depth erosion, diminished summer flows, and low water quality during the summer.

In response to this situation, Artificial Beaver Dams or Beaver Dam Analogues made of wooden stakes and willow branches have recently been developed in the US as nature-based solutions to reduce bed incision in small streams. At Southampton University, we are looking at beaver dam inspired rock- and wood structures as nature based solutions for water retention and stream restoration.

Beaver dams are usually built from wood. If there is not enough wood available, beavers build dams from rocks with diameters of 250 – 300 mm, using wooden branches as reinforcement. At Southampton University, this type of composite dam was tested at model scale. Composite dams were significantly stronger than dams made up of gravel only. The tests showed that a composite dam of 1.4 m height fails at a flow of 2.28 m³/s per meter width, whilst a gravel-only dam already failed at 0.06 m³/s·m.

A further series of 1:10 scale tests was conducted to assess the effect of scouring on dam stability. Three different scenarios were investigated: (1) solid bed - benchmark, (2) dam built on sand bed, (3) dam built on a geotextile.

The dams failed at a flow volume of 2.24 m³/s (full scale) and meter width (benchmark), 0.90 m³/s·m (sand, no geotextile) and 1.36 m³/s·m (sand with geotextile). This constitutes about 40% (no geotextile) and 60% (with geotextile) respectively of the failure flow of the dam structure with solid bed.

It could be concluded that the beaver’s rock-and-wood construction method offers a very strong, flexible and cost-effective nature based solution for the restoration of small streams to reduce depth erosion and increase water retention.