By Seth Wilkinson
Harder isn’t always better when it comes to stabilizing your shoreline
In the wake of Hurricane Sandy, this is the time to consider our coastal resources and how to best manage them while also protecting coastal property. When it comes to coastal stabilization, engineers, ecologists and coastal geologists often differentiate between hard and soft alternatives. Examples of hard alternatives are stone revetments, wood, steel or vinyl 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 specialists 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 such as salt marshes and beaches. Wilkinson Ecological Design specializes in soft alternative strategies which we refer to as plant-focused strategies for coastal erosion as it is the plants which provide the long-term stability rather than the materials which initially hold the sediments in place.
So what is the problem with “hard alternatives”? At a most basic level, hard alternatives tend to reflect or re-direct the energy in waves to other nearby areas. While some hard alternatives absorb energy better than others, they tend to move the problem to another area rather than absorbing the wave energy. The key thing to remember is that our shoreline is an intrinsically dynamic system that is constantly changing, whether 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, coastal structures become a barrier to migrating coastal plant communities, which need to move landward or increase in elevation to survive the rising sea level. Without a regular supply of sediment from upland landforms to maintain the necessary elevation above the rising sea, coastal plants do not survive. 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 or a growing medium(not rocks, wood or concrete) into which a salt marsh may move (or migrate). An appropriate, plant-focused soft strategy offers both of these conditions.
While there are clearly some instances when only hard alternatives are feasible to protect property and homes, many less-severe erosion issues can be addressed through the use of plant-focused soft alternatives. The recent Hurricane Sandy and the Nor’easter which followed a week behind were two high energy storms which provided a test to most coastal stabilization strategies on the Cape and Islands among other places. The success with which our plant-focused alternatives weathered the latest storms is very encouraging; offering a feasible alternative to the more conventional hard alternatives which tend to lower beach elevations and exacerbate erosion in adjacent unprotected areas. 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-focused 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 are one of the most ecologically productive plant communities in the world and play a key 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 advanced planning it is possible to achieve the desired protection of property without losing the function of our coastal resource areas.
-Seth S. Wilkinson, MALD is President and Restoration Ecologist at Wilkinson Ecological Design, Inc. and is a resident of Orleans.