https://www.researchgate.net/figure/Stabilized-inlet-where-jetties-impede-sand-flow-parallel-to-the-barrier-beach-reducing_fig2_235019634
The first example of hard stabilization that we will examine is a jetty. Jetties are pairs of long offshore barriers that are constructed on either side of inlets. They are usually made with concrete or tightly clustered formations of large rocks, and they frequently extend hundreds of feet into the water. The most common use of jetties is to construct them parallel to one another, with a maintained channel in between for ships. They are thus used as entrances to harbors (usually along sandy beaches), as they guarantee an opening along the coast. A similar implementation can also be found around docks when they are used to berth ships. In both cases, they are generally permanent structures that are immobile and large enough to safely hold back the tide on either side.
While the uses of jetties are indeed critical to the shipping of goods, there are significant drawbacks as well. The most noteworthy of these limitations is the occurrence of downdrift beach starvation, resulting from up drift sediment accumulation as shown in the diagram below. The latter phenomenon is simply the buildup of sediment on the up drift side of a jetty because the structure prevents longshore currents from carrying the sand along the beach. Similarly, downdrift starvation occurs on the opposite side of the jetty, which becomes starved for sand, causing the erosion of the beach along that side to accelerate. Because jetties are larger in size than most other hard stabilization strategies, the lack of downdrift sediment severely depletes the beach and has the opposite effect of stabilizing the shoreline.
In addition to this beach starvation, jetties are especially damaging when they are built along the coast of barrier islands, because these islands naturally migrate inland. The jetties, however, severely disrupt this migration by halting the longshore movement of sediment. This impacts the health of the wetlands behind the island, while also harming the equilibrium of the beach.
As a result of these critical consequences, the construction of jetties to prevent shoreline erosion has become fairly uncommon. Unfortunately, they are still frequently erected to allow for shipping to continue at ports and harbors, and the consequences of downdrift starvation and wetland destruction become unavoidable in these areas.
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