Freedom to Roam: How Meandering Rivers Can Decrease Destructive Flooding

By Mike Kline, Vermont Rivers Program

Few people have every followed a linear path in life. We are dynamic individuals and have a tendency toward straying off path – adventuring in new directions. Our rivers are no different. It may be tempting to look on a map and see a river as its drawn – a winding line of blue – and expect these bodies of water to continually follow the same path. Yet, just as we cannot be kept to a singular path in life, the journey of a river cannot be constrained to a single line. Scientists with the Department of Environmental Conservation’s Rivers Program are hard at work using stream geomorphic assessments to help mitigate flooding by managing for a river’s meanders.

Flood mitigation is all about finding balance in nature. There is a growing knowledge that balance happens between a river and its floodplain, allowing for meanders and accepting the paradox of moving but stable riverways. Understanding this has become critical to restoring riverine ecosystems and improving our resiliency after floods. 

Giving room for the river by defining a freedom space for the river are cost-effective methods to promote the equilibrium processes that restore floodplains and reduce flood damages.

In Vermont “river corridor protection” is practiced, giving rivers a freedom space within their “meander belt”. A “meander belt” is the corridor of land encompassing a stream’s natural meanders. If one knows the valley shape and the drainage area of a straightened river (e.g., the 1924 channel of the Third Branch pictured above), then a meander belt can be calculated to accommodate the length of the river as it evolves towards its natural stream processes and equilibrium (e.g., 1939 through 2003 channels in the picture above). Mapping the minimum space that a straightened river would need to achieve its most vertically stable, least-erosive form, serves as a science-based planning tool to restore riparian ecosystems and avoid flood-related erosion hazards.

The Vermont Rivers Program has worked with many local partners to collect stream geomorphic data and define corridors for 5,500 miles of rivers and streams.  Nearly three-quarters of Vermont streams are incised and are at a midway point in their evolution toward equilibrium. An incised channel has deepened through erosional down-cutting (i.e., as shown between the channel cross-sections of Panel A and Panel B in Figure 1). These incisions are usually human-caused, to drain and improve nearby land through channel straightening, dredging, ditching, and berming. These deepened channels prevent the rivers from flowing onto floodplains.

When these rivers are no longer allowed to flow onto natural floodplains, the result is increased erosion – meaning damaging floods, greater toxic algal blooms, and decreased river and riparian habitats. The daunting challenge is figuring out how to reconnect rivers with their floodplains to restore and protect the natural channel evolution process.

One way to do this is through the River Corridor Easement tool. In a river corridor easement, the landowner sells both the development rights and the channel management rights, meaning, within the river corridor, only the holder(s) of the easement have the right to manage the movements of the river.  This provision of the easement ensures that the river will be free to move, develop floodplain, and adjust to an equilibrium condition. 

River corridor easements have become popular, particularly with those who have begun to see their struggle with river erosion as a losing proposition. To date, the state and its conservation partners have completed over 80 of these easements on some of the most sensitive (erodible) reaches of river in the state.  Promoting natural floodplain function through river corridor easements has become one of the relatively low-cost methods for reducing the 22% phosphorus load to Lake Champlain attributable to unstable streams. Phosphorus captured and stored on a floodplain improves soil fertility, but will not contribute to algal growth and cyanobacteria in the Lake.

While the act of straightening and berming rivers has largely ended, the loss of these meanders combined with more frequent extreme weather events keeps us vulnerable every time the rains fall hard. Vermont roads and settlements were made along the rivers, and so we must spend the money to manage and contain certain river segments. But with every new riverside development that requires more flood containment, the costs to the whole community will continue to rise. A cascade of river controls that always require repair, becomes unsustainable, especially as the frequency of flash floods increases with climate change.

There is a cost to keeping river corridors free of new encroachments. Buying easements, cost-sharing home buyouts, and redirecting new development so that rivers can continue to evolve, re-form meanders, and create new floodplain. However, this approach will be a fraction of the cost of repairing and rebuilding after floods and continually chasing our rivers with hard armor.  We will also need patience.  It took hundreds of years to alter the landscape and the course of rivers, and it will take decades of private-public partnership to manage them back toward a stable equilibrium condition.

Rivers Program contacts and information about river corridor protection may be found at the following links:

http://dec.vermont.gov/watershed/rivers/river-corridor-and-floodplain-protection

http://dec.vermont.gov/watershed/rivers/river-corridor-and-floodplain-protection/river-corridor-planning-and-protection