As with hard stabilization there is a wide variety of methods under the umbrella term of soft stabilization that aim to preserve the beaches and coastlines as they are. The various types of soft stabilization share the aim of beach preservation but attain this through different methods and all come with their own unique pros and cons that will be discussed later. First, we must understand the different types of soft stabilization and the mechanisms that they utilize to protect the shorelines without being as invasive as some hard stabilization methods.
Sand Replacement / Beach Nourishment
This method of soft stabilization involves the replenishment of sand/sediment to the beach and shorelines, often through pumping the sediment from elsewhere and depositing it onto the beach to replace what is constantly being eroded away. The source of this sediment may vary depending on the particular situation, for example, if the nourishment is occurring adjacent to an inlet the sediment will often be pumped from the channel to the beach in order to clear the channel while nourishing the nearby beach. Other potential locations for the sediment being pumped onto the beach from is offshore of the beach from the ocean floor or at the mouth of an inlet to prevent any delta formations that could cause the inlet to become unnavigable.
With many of these less invasive forms of beach stabilization, the fix that beach nourishment provides is very temporary. Erosion is a constant force and as such these beaches that are being nourished by alternate sand sources must have sand replacement performed every few years to keep up with the erosion that is occurring, especially if in a high energy environment. Another major downfall of beach nourishment is that it is very expensive because it is a continuing, cyclic process of nourishment, erosion, and repeating. Also, the machinery that is required for this sand replacement is expensive to acquire and equally expensive to run. A more ecologically focused drawback of beach nourishment is the importance of matching the sediment that is being deposited on the beach. Depending on the type of sediment being pumped onto the beach, replacement sand can sometimes choke out the beach by clogging the pores within the sand which deprives organisms that live in the sand of both oxygen and food.
Sand Dunes
Sand dunes go hand in hand with beach nourishment as they are important in retaining sand that is washed ashore or blown around. The dunes collect this sand in order to build themselves up and counteract the constant erosion that these coastlines see while simultaneously providing flood protection from storm surges or hurricanes. This sand collection can be performed in a multitude of ways but the two most common are through planting vegetation, like native grasses and reeds to catch this windblown sand, or installing small fences that run perpendicular to the shoreline in order to catch sand that is being blown down the beach.
Obviously, the major benefits of sand dunes are that they protect the land behind the beach and in turn, they protect the houses and infrastructure that lies just beyond the dunes. However, there are ecological benefits derived from stabilizing and promoting dune growth such as the growth of native grasses that inspires native organisms to inhabit these dunes and completely restore the native ecosystem that has been decimated by human activity. Once the establishment of these ecosystems occurs it will become a more self-sustaining system in terms of catching sand to continue the growth and stabilization of the sand dune in order to better protect the land just beyond them. Another benefit is that this is a very inexpensive method to protect the coastlines and is one of the least invasive in terms of environmental impacts. However, the major drawback of sand dune stabilization is that it is on a much longer time scale, especially compared to hard stabilization where results are seen much sooner after implementation.
Green Stabilization
Green stabilization is a term that involves more environmentally focused erosion control and beach preservation. Often this comes through planting native grasses and inspiring colonization of native animals to boost the overall health of the nearshore and coastline ecosystems. This concept involves more than just the beach itself, as it includes the ways in which the beach is preserved in conjunction with local infrastructure, namely beachfront properties. Green stabilization emphasizes pollution control and habitat preservation through environmentally conscious construction of beach stabilizing structures as well as private homes that are nearshore. By promoting native grass growth and soil retention, pollutants can be better filtered out and erosion can be better controlled as these plants can stabilize wave-battered soils. In terms of nearshore infrastructure, this type of stabilization relies on environmentally conscious construction, especially in terms of impervious surfaces as to reduce stormwater runoff and the erosion that is can cause. At its core, Green Stabilization starts with a base of softer stabilization structures that are environmentally and ecology conscious and help spur ecosystem health for native plants and animals.
Green Stabilization is one of the more all-encompassing methods of shoreline stabilization and considers that nearshore areas can also contribute to coastline degradation. This methodology is a more wholistic approach to erosion control and coastline stabilization as it recognizes the impacts that nearshore infrastructure, and urbanization as a whole, can have on the shoreline ecosystem and its integrity. However, this concept is a fairly new one and has been implemented in few places so there is little long-term evidence that can be studied in order to fully understand its effectiveness. Considering this, it is difficult to determine if this is the methodology that could shape the way we think about coastline stabilization in the future, but it is one of the most all-encompassing methods and could prove to be the most effective as it is used more often.
Other Alternatives
Beyond the above, more mainstream methods of soft stabilization there are others that are used less often but can still be beneficial to the environment. These alternative methods continue with the theme of being less invasive than that of hard stabilization, but they may also be effective for more specific situations and may not apply to every coastline degradation situation.
Dewatering beaches is a potential solution that offers a very minimally invasive method of erosion protection. This method involves pumping out groundwater from the beach face, and thereby lowering the water table at the shoreline, in order to allow water to more easily infiltrate into the sand. This increased infiltration allows the water to go into the ground rather than crashing onto the shore and eroding sand away as it retreats. Also, as the waves hit the shore and infiltrate, they deposit their sand loads which can actually help grow the beach. Though there are two different ways in which this method helps preserve the coastline, the implementation is difficult as the beach must be outfitted with an underground pumping system and these pumps must run constantly to see the benefits that this method can provide.
Another method of soft stabilization, one that has found a loophole in classification, is the use of large sandbags in order to protect infrastructure from the encroaching coastline. These massive sandbags are sometimes as big as five feet cubed and filled with sand and are placed in lines, often in front of beachfront homes, to prevent intruding waves from battering the houses. This method, specifically in North Carolina, utilizes a loophole in the ban on hard stabilization measures as these bags are technically removable, and therefore they are not considered hard stabilization while they practically function as such. These sang bags, when lined together, create what acts as a bulkhead and creates a hard line where the water stops and where erosion is exacerbated. Because of the impenetrable wall of sand water rolls over itself and cuts the sand out in front of them and eats away the beach until the water comes right up against the bags. This method, although useful for stopping the water from damaging houses and infrastructure in the nearshore area, is detrimental to the preservation of the beach as it operates very similarly to hard stabilization techniques. The main benefits for this method are that it is effective in protecting the infrastructure beyond the sandbag line, they are fairly inexpensive, and they are easily removable which is useful as these are everchanging environments.
Works Referenced:
http://concretebasics.org/articles/soft-stabilization-coastal-defense/
https://www.islandcountywa.gov/Health/DNR/Documents/Soft%20Shore%20Stabilization_ECY.pdf