Designing Living Shorelines for New England Coasts

The Process

New England’s severe winter storms cause erosion that can devastate coastal properties. Winter storm Juno on January 28, 2015, was no different, battering the region with heavy snow, coastal flooding, and tropical-storm-force winds. For one property owner in Orleans, Massachusetts, Juno demolished an erosion-control structure of plantings and bank nourishment. Every cubic yard of sand previously brought in was washed away, and a steep bank was scoured out again and again by Juno and subsequent storms. It was time for a more robust shoreline management approach.

The property owner moved ahead with Massachusetts’ strict regulations in mind. In decades past, engineered seawalls or revetments were used to protect eroding shorelines. Now, in most cases, the state requires softer erosion-management methods such as vegetation that buffers wave energy, maintains natural sediment movement, and is more attractive than engineered structures.

Noticing that some neighboring properties experienced no erosion from Juno, the owner learned that coconut fiber rolls and pillows (also known as coir products) had been used to control erosion. When properly selected and laid down, these materials dramatically slow water velocity at the base of slopes, shorelines, and stream banks. Seth Wilkinson, the project manager and president of Wilkinson Ecological Design, learned that this owner’s property was a good candidate for the same method because of its stable base elevation, fringe marsh, and offshore sandbar.

Designing Living Shorelines for New England Conditions

In the past, shoreline management projects were either designed by ecologists without the aid of engineers, or by engineers who might bring ecologists in at the end to put some green in the project.

By contrast, Wilkinson works with an engineering firm to develop a survey and site plan and collaborate on design details and the review process. The collaboration benefits projects confronting extreme New England conditions such as large tidal ranges, winter ice, fierce nor’easters, and wakes from seasonal boating, which all contribute to erosion.

A related NOAA project that interviewed living shoreline practitioners in New England backs up this approach. “As projects are installed farther north, they become more difficult,” says Andrew Rella of the Stevens Institute. “This is why we need both engineering and science: to create well-designed projects that perform functions.”

For this project, a rigorous site analysis to assess physical forces, slope, water levels, wave heights, and other site characteristics was essential. As a lifetime resident of the Cape Cod region, Wilkinson also considers anecdotes an essential aspect of gathering information on both past and present conditions.

During the winter, tidal ice flows enter salt marsh and the ice often bonds to the marsh, picking up sediment and moving it while also pulling out the upper level of peat. This can cause severe damage to anchored plantings and coir products that control erosion. Small boulders and rocks can be placed in the area for protection, but that adds to the permitting hurdles.

For durability, Wilkinson incorporates a higher mean high water base elevation figure into this kind of project. Doing so increases sturdiness against both present and future conditions.

Wilkinson’s design reinforced the toe of the steep slope with coconut fiber rolls and pre-vegetated coir pillows, which will help him gather data about which species are best and the feasibility of future fringing salt marsh options. Diverse planting will enhance the wildlife habitat function.

More robust alternatives are being used to secure bioengineering measures, given the increased frequency and intensity of coastal storms. “Some people say you cannot use fiber rolls in high-velocity zones, but I have installed miles of successful fiber roll arrays in high-velocity zones. However, if you do not pay attention to details you will find out in the first storm that your rolls have failed,” says Wilkinson. “It is important to understand that not all coconut fiber rolls are created equal. Part of my job is to constantly educate people about this.”

Tools Used

Detailed design guidance is hard to come by. Wilkinson has developed his own detailed design criteria to help streamline the design process according to site conditions. The Federal Emergency Management Agency’s Federal Insurance Rate Maps are a resource for determining whether a site is in the velocity zone or would experience still water flooding. A property in the velocity zone signals the need for a more robust design.