• Brooke Reynolds


Before leather-booted colonists with their own rigid ideas of progress stepped onto the shores of America, beavers defined the landscape. Since shortly after the last ice age ended, America’s riparian systems were defined by an intricate arrangement of seeps, bogs, wetlands, beaver dams, floodplains, and branching streams and rivers woven into a harmonious tapestry. The keystone species orchestrating this river dance was Castor canadensis, the American beaver. Beavers were not only engineers, they were artists. Nearly every creek would have exhibited a chain of beaver dams, sculpting entire ecosystems of braided streams and wetlands. Dams keep more water on the land, so America was a much soggier landscape.

Beaver dam at U&A's Howard's Branch Restoration

As a keystone species, beavers create conditions in the ecosystem upon which other species rely. Their ponds are 7 times more bio-productive than fertile farmland (beaverinstitute.org). When beavers impound an area, trees not adapted to flooded conditions die. Termed “snags,” these trees lose their branches over time, remaining upright or eventually toppling, and become food, shelter, and perches for species such as wood ducks, eagles, woodpeckers, turtles, and herons. Beavers create different elevations when they excavate banks for their burrows and their “transportation” canals. This in turn encourages various types of insects to thrive and allows everything that eats those bugs to flourish. The natural system of beavers building and intermittently abandoning their dams provides additional benefits: filtering pollutants, catching silt, preventing erosion, and encouraging groundwater infiltration and seepage that often results in cooler waters downstream.

The vivid imagery of this pristine, wild system of dynamic equilibrium can nearly cause one to forget that this story has a sad ending. Brought down by the beauty and warmth of their own pelts, the great American beaver dynasty ended with the Colonial era in America. Throughout the 17th and 18th centuries beavers were hunted and trapped in great quantities to be exported to Europe. The demise of the beaver began the degradation of the intricately woven riparian systems, contributing to the fundamental change in stream habitat, hydrology, and channel stability.

Before environmental regulation, demands for land resulted in encroachment and building on sensitive habitat. Stormwater surface flow was sent to pipes and then out to the nearest stream, resulting in the straight, deep cuts of stream channels we see today. There was an incomplete understanding of the damage being done to floodplains, bogs, and marshes. Streams, rivers, lakes, and bays are still impacted by sediments, excess nutrients, and toxics. Surface water is largely disconnected from groundwater, contributing to long-term water level declines that will become increasingly more apparent in the near future.

The isolated, straight stream lines fashioned by humans stand in stark contrast to the brushstrokes created when the beaver painted the landscape. It is difficult to imagine the elegant beaver-engineered habitat 400 years prior in the exact same place as an eroded stream bed or solitary ribbon of blue through a city, suburb, or farm. Some may naturally assume streams have always looked this way. We are a thousand threads lacking the beaver’s touch to weave our lands together into a quilt of interconnectedness. How can these areas become connected and function as they once did? How can we mimic the pristine ecosystems of the past in a time of anthropogenic impact?

Simply using beavers to perform the ecosystem services they once did seems like an obvious answer. In fact, in many parts of the country where there is ample open space, beaver may be placed to further build where beaver dam analogs (BDAs), structures similar to beaver impoundments, have been built. However, we do not have the sufficiently large beaver populations in Anne Arundel County or much of the East Coast to rely on them to restore streams to pre-colonial conditions. Dams require constant maintenance and a robust beaver population in order to remain functional. If beavers are trapped out of an area or decide to leave, their dams will eventually fail if not meticulously maintained. Additionally, beavers (with understandably no concern for our human infrastructure) will often flood areas that adversely affect our built environment. Beavers are accustomed to operating in an entire system, but in the segmented natural areas that are the realities of today, there are few options for beavers to migrate or adopt their natural patterns.

Underwood & Associates created the Regenerative Stream Channel (RSC) and Step Pool Stormwater Conveyance (SPSC) restoration methods using a landscape approach to improve and advance habitat recovery over time to closely approximate native ecosystems. U&A designs use biomimicry to achieve outcomes similar to beaver dams, incorporating a series of riffle weirs, sand seepage berms, and step pools that slow down and spread out water in a more predictable and sustainable manner than beaver impoundments. This results in the trapping and filtering of pollutants, enhanced floodplain connection, groundwater infiltration, erosion prevention, and habitat creation.

Although RSCs and SPSCs can mimic the benefits of beavers, how do these iconic mammals fit into restoration projects? It is common for beavers to move into restoration sites after they are completed. The beavers will often begin building dams on top of the existing weirs. The dams built on weirs can raise the water level in the ponds a few feet higher than original restoration plans may have expected. The added weight of the extra water may cause weirs to “blow out.” Therefore, a beaver-friendly restoration project must be hardy enough to accommodate the rising and falling of water levels as the beavers make their own modifications to the site. Underwood & Associates welcomes beavers that take up residence on all of our restoration sites, since our projects are created to be resilient enough to incorporate the changing conditions and fluctuations of nature.

If beavers are to have a place in the current landscape configurations of modern America, we must make space for them. More land conservation is needed to provide ample habitat and connected stream systems for beavers to inhabit. Restoration projects should be designed with resiliency and adaptation in mind to account for changes beavers may make. Non-jurisdictional (less than one acre) wetlands such as bogs, marshes, and wet meadows should be protected from degradation and development. Benefits would reverberate across our ecosystems if we could more clearly visualize and implement designs that re-create the knitted systems of the past where seeps and headwater streams meandered through wetlands, floodplains, and beaver impoundments. If we make greater efforts to connect these freshwater habitats to downstream brackish marshes, estuaries, and coastal bays, the entire system would thrive by being more integrated. Restoration and conservation present our only opportunity to realize this vision, to connect and unify natural hydrologic systems, and to mend the modern landscape to regain a semblance of the days when beavers were the composers orchestrating the ecosystem.

A beaver impoundment built on top of a weir captures water from a heavy summer rainstorm at Howard's Branch