When a waterfront property owner watches the lake eating away at their backyard, the instinct is to fight back. Stack rocks along the shore. Build a seawall. Armour the bank with concrete and steel. These hard protection measures can be effective at protecting an individual property from erosion, and they are a common sight along Ontario shorelines. But the growing body of evidence suggests that shoreline armouring, particularly when done piecemeal along a stretch of coast, can create as many problems as it solves.

The term shoreline armouring refers to the installation of hard, engineered structures along the water's edge to prevent erosion. These include concrete and steel seawalls, gabion baskets filled with rock, rip-rap consisting of large stones placed along the bank, sheet piling driven into the lakebed, and various combinations. The structures are designed to absorb or deflect wave energy and hold the shoreline in place. For the property they protect, they often work. The question is what they do to everything else.

How Armouring Redirects Energy

Water does not stop moving because it hits a wall. Wave energy that would naturally be absorbed by a sloping beach or a vegetated bank is instead reflected off a hard surface. This reflected energy travels outward, often intensifying erosion on adjacent unprotected shoreline. The property next door, which may not have had an erosion problem before the neighbour armoured their shore, can find itself suddenly losing land. This phenomenon, sometimes called flanking or end effect erosion, is one of the most well-documented consequences of piecemeal shoreline armouring.

Hard structures also prevent the natural process of sediment exchange between the upland and the nearshore. On a natural shoreline, erosion of the bank provides sediment that feeds the beach and the nearshore environment. When a seawall prevents this erosion, the beach in front of it gradually narrows and may eventually disappear, because the sediment that maintained it is no longer being supplied. This process, called passive erosion or coastal squeeze, is particularly visible on the Great Lakes, where armoured shorelines often have a deep-water drop-off directly in front of the wall where a gradual beach slope used to exist.

Ecological Impacts

The ecological effects of shoreline armouring are significant and well documented. Hard structures replace the complex, varied habitat of a natural shoreline with a uniform surface that supports far fewer species. The spaces between rocks in rip-rap do provide some cover for fish and invertebrates, but they are a poor substitute for the diverse microhabitats created by natural vegetation, fallen wood, root systems, and varied substrate.

Seawalls eliminate the transition zone between land and water that is critical for many species. Amphibians that need to move between terrestrial and aquatic habitats find vertical walls impassable. Turtles that need sandy or gravelly banks for nesting are excluded. Shorebirds that feed along the wrack line lose foraging habitat. The cumulative effect of armouring along a stretch of shoreline is a significant reduction in biodiversity.

The loss of natural shoreline also affects water quality. Vegetation along natural shorelines filters runoff, absorbing nutrients and trapping sediment before they reach the water. Armoured shorelines provide no such filtration. Runoff from the developed property behind the wall flows directly into the lake, carrying whatever pollutants it has picked up along the way.

The Regulatory Framework

In Ontario, shoreline armouring is regulated by conservation authorities under the Conservation Authorities Act and may also trigger review under the federal Fisheries Act if it affects fish habitat. Conservation authorities generally prefer naturalized shoreline approaches over hard armouring and may require that applicants demonstrate why softer alternatives are not feasible before approving hard protection measures.

Despite these regulatory frameworks, a significant amount of shoreline armouring occurs without proper permits, particularly on smaller projects that property owners undertake without realizing that approvals are required. The cumulative impact of these unpermitted works contributes to the broader problem of piecemeal armouring along Ontario shorelines.

Better Approaches

The engineering and environmental science communities increasingly advocate for approaches that work with natural processes rather than against them. Living shorelines, which use native vegetation, natural materials, and strategic grading to stabilize the coast, can provide erosion protection while maintaining ecological function. Hybrid approaches that combine a rock toe for wave protection with a vegetated slope above can be effective on moderate-energy shorelines.

Where hard protection is genuinely necessary, such as along high-energy Great Lakes shorelines protecting critical infrastructure, good engineering design can minimize the negative effects. Sloped rather than vertical structures reduce wave reflection. Toe protection designed to dissipate rather than reflect energy reduces flanking erosion. Incorporating habitat features into the design of hard structures can partially offset the loss of natural habitat.

The fundamental message is that shoreline armouring should be a last resort, not a first response. Before reaching for the rocks and concrete, property owners should consult with their conservation authority and a qualified shoreline professional about whether natural or hybrid approaches could achieve the same protection with fewer side effects. The shoreline is a shared system, and what you do to protect your property has consequences for your neighbours and for the ecosystem.

By James Whitfield, Planning and Development Reporter