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"Hard" Scapes

Erosion at Wasque, Chappaquiddick. Photo by Dana Gaines

The Problem with Revetments and other “Hard” Structures

When it comes to coastal stabilization, engineers and coastal geologists often differentiate between hard and soft alternatives. Hard alternatives are typically stone revetments, wooden, steel or concrete bulkheads, or other similar structures. Soft alternatives usually range from arrays of coconut fiber (coir) rolls, erosion control matting and sand-filled biodegradable envelopes to various methods of harvesting wind-blown sand, known as sand drift fencing. 

As a company that specializes in ecological restoration, we see these “soft alternatives” as tools to hold sediment in place long enough to re-establish a native plant community, which will in turn restore stability to coastal landforms while still allowing them to play their critical ecological function as wildlife habitat and provide a sediment source to other near-shore areas.  We refer to these soft alternative techniques as plant-centered strategies for coastal erosion.

So what is the problem with the “hard alternatives”?  The first thing to remember is that the shoreline is an intrinsically dynamic system that is constantly changing, whether it be from sea level rise, coastal storms or various forms of human-induced erosion due to everything from boat wakes to scour from other coastal structures.  The coastline is primarily made up of a matrix of beaches and salt marsh plant communities which must be able to move and change shape to stay vibrant, healthy and diverse.  When the shoreline is hardened, plant communities may no longer migrate. These intertidal areas also require a regular supply of sediment from upland landforms to maintain proper elevations above the rising sea level.  The method by which plant communities migrate differs from animal migration and, as one can imagine, is much slower. In order for this migration to occur, two major conditions must be met;  there must be a source of sediment to nourish the migrating root systems, and there must be land area (not rocks, wood or concrete) into which salt marsh may move (or migrate).

While there are clearly some instances when only hard alternatives are feasible, many erosion issues can be addressed through the use of plant-centered soft alternatives. When bio-engineering products such as fiber rolls and erosion control matting are used to re-establish native plant communities, the critical function of the upland interface with the intertidal areas are preserved, allowing the salt marsh plants to migrate landward.  During storm events, areas which have been stabilized with biodegradable materials and native plants are often impacted by waves, wind, and storm surges, resulting in a periodic supply of sediment to the beach or salt marsh community.  While plant-centered soft alternatives tend to require more frequent maintenance and repairs after intense storm events than hard alternatives, they serve to protect critical salt marsh functions and allow these plant communities to migrate and thrive. Hard alternatives prohibit sediment from reaching beaches and salt marshes, and therefore prevent the migration and establishment of these critical plant communities. It is important to remember that salt marsh communities play a role in storm damage prevention, the attenuation of pollutants, and are critical nursery areas for many fin and shellfish species with both recreational and commercial value.

It is time we start giving proper attention to the importance of our intertidal environment’s ecology and consideration of salt marshes and beaches when determining the best method for stabilizing coastal landforms as well as protecting property along the coast.  With a good understanding of coastal ecology and proper planning it is possible to achieve the desired protection of property without losing the function of our coastal resource areas.

Seth S. Wilkinson, Restoration Ecologist Wilkinson Ecological Design, Inc.