Hard armouring outperforms a biomass-based living shoreline on a high-energy, ice-influenced sandstone coast: a one-year controlled comparison at Augustine Cove, Prince Edward Island, Canada

Coastal communities around the world face a relentless choice when the ocean begins to eat away at their land. They can retreat, moving their homes and infrastructure inland to let the water take its course; they can accommodate, building structures that rise with the rising tides; or they can defend, building barriers to hold the sea back. For decades, the standard defense has been hard engineering: massive walls of concrete or stone designed to bounce waves away. But in recent years, a different philosophy has gained traction. This approach, often called a "living shoreline," seeks to stabilize the coast using natural materials like plants, logs, and soil, hoping to create a buffer that absorbs wave energy while supporting wildlife. The idea is that nature can be a better engineer than a bulldozer. However, most of the success stories for these living shorelines come from calm, sheltered bays in the southern United States, where the water is gentle and the ice never freezes the shore. It remains a mystery whether these soft, biological solutions can survive the brutal, freezing, and wave-swept conditions of the open ocean in places like the Gulf of St. Lawrence.

On the south shore of Prince Edward Island, Canada, a unique natural experiment unfolded to answer this question. A single property, home to a seasonal children's camp, offered three distinct sections of coastline sitting side by side, all exposed to the same fierce waves, the same freezing winter storms, and the same soft, crumbling red sandstone cliffs. One section was protected by a traditional stone seawall built in 2009. A second section, installed just a year before the study began, featured a living shoreline made of brush, hay bales, logs, and native plants. The third section was left completely alone, serving as a control to show what happens when no one tries to stop the erosion. Researchers spent a full year watching these three neighbors, measuring exactly how much land each lost to the sea. They used simple steel tapes anchored to the ground and high-resolution drone photography to track the edge of the cliff with extreme precision.

The results were stark and unexpected. Over the course of that single year, the stone seawall held its ground almost perfectly, showing no measurable retreat. In contrast, the living shoreline lost ground at the exact same rate as the unmanaged, unprotected section. The natural barrier of logs and plants did not slow the erosion at all; it performed as if nothing had been installed. The living shoreline retreated nearly half a meter, a distance statistically identical to the bare cliff next to it. This failure was not due to a lack of effort or funding; the living shoreline cost roughly twenty thousand Canadian dollars to install, a significant investment that was ultimately ineffective against the specific forces at play. The stone wall, costing slightly more, had successfully stopped the water from moving the land.

The researchers found that the living shoreline failed because it was the wrong tool for the job. The design used was a "brush-and-biomass" approach, relying on unanchored logs and plant roots to hold the soil together. This type of design works well in the calm, ice-free estuaries of the American South, where waves are small and the ground is stable. But on Prince Edward Island, the conditions are far more violent. The waves travel over a vast stretch of open water, building up tremendous energy before hitting the shore. Furthermore, the winter brings a unique set of dangers: the water freezes, and the ice itself pushes against the land, scouring the base of the cliffs and breaking up the soft sandstone. The living shoreline was installed in late summer, giving the plants only a few weeks to establish roots before the autumn storms hit. The first winter storms were enough to wash away the unconsolidated materials, and by the following January, a third of the structure had been completely stripped away by the sea.

The study also revealed a hidden danger of the stone seawall. While the wall protected the land directly behind it, the section of coast immediately next to the wall, where the protection ended, began to erode faster than any other part of the property. This phenomenon, known as flanking, occurs when a hard barrier reflects wave energy sideways, attacking the unprotected land at the ends of the wall. The data showed that the area just beyond the seawall was losing land at a rate more than double the average of the rest of the property. This suggests that while the wall saved the specific patch of land it covered, it may have accelerated the loss of the neighboring land, a trade-off that is often overlooked in coastal planning.

The researchers are careful to state that this does not mean living shorelines are useless everywhere. The failure was specific to this one location, this specific design, and this particular combination of high waves and freezing ice. The study does not prove that nature-based solutions cannot work on the open coast, but it does prove that the blueprints used for calm bays cannot be copied and pasted onto the rugged, icy shores of the Gulf of St. Lawrence. The design installed here lacked a solid, wave-dissipating foundation, such as a rock sill, which is often present in the successful examples from the United States. Without that hard anchor, the soft materials were simply no match for the winter storms.

This case study serves as a critical warning for coastal managers and landowners in Atlantic Canada. It highlights that the decision to build a living shoreline is not just about choosing a "greener" option; it requires a rigorous assessment of the local environment. Before installing a natural barrier, planners must consider the length of the open water the waves travel over, the presence of sea ice, and the type of rock or soil making up the cliff. The study suggests that in high-energy, ice-influenced environments, the menu of viable options is much narrower than often assumed. For some places, the only realistic defense might be to move back from the water's edge, a strategy known as managed retreat, rather than trying to fight the ocean with a design that the local conditions will inevitably defeat. The evidence from Prince Edward Island shows that without local, site-specific engineering and a deep understanding of the winter ice, even the most well-intentioned natural defenses can crumble under the weight of the sea.