Engineers build shoreline structures mainly for two purposes: (i) For prevention of destruction of sea coasts by waves and currents, and (ii) For improvement of navigation. The chief shoreline structures are as follow:
(1). Sea Wall: Sea walls are massive structures built to protect the areas lying immediately in their rear from the damaging wave action. They are built parallel to the coastline. The sea walls range from a simple rip-rap deposit to regular masonry retaining walls.
(2). Groynes: A groyne is a wall-like structure, which is built at right angles to the coastline. It checks littoral drift and causes deposition. In this way a beach is created, which protects the coast against wave action. Groynes are generally made up of steel sheets, concrete blocks, stones, and creosote wood.
Different Types of Gryones:
Stone Groynes: Stone groynes are among some of the more straightforward groynes to build because separate, irregularly-shaped rocks in a rough formation comprise them. This means that it is possible for builders to source the stone materials from the leftovers of other construction projects since it does not need a pristine appearance nor components with precise dimensions. Due to the fact that the rocks have spaces between them, stone groynes are highly capable of soaking up the strength of waves, as they take in and disperse the force in addition to blocking it outright. Should the needs of the coastline shift over time, it is also relatively easy to dismantle these groynes and reconstruct them in new positions. Additionally, rocks in and of themselves are desirable materials for erosion protection applications because they remain firm while in constant contact with water. The downside of stone groynes is that those same gaps that make them so effective can also allow for some sediment to pass through.
Concrete Groynes: Concrete is a common material for groynes because of its impressive resilience. Concrete groynes will remain largely unchanged for extended periods and can include reinforcements to make it even more solid. These come in the form of steel bars that exist as a sort of internal skeleton around which the concrete solidifies. The steel takes on a sizeable amount of the stresses that the concrete faces, which keeps the concrete from cracking as readily or otherwise breaking down in the face of waves. Since professionals usually prefabricate concrete groynes’ parts and then assemble them at the shoreline site, these groynes have a smoother and neater appearance than some of the alternatives on this list. The main issue with concrete, however, is that it is heavy. As such, concrete groynes are only feasible in areas with the proper ground to support the weight of their foundations and their main bodies.
Wooden Groynes: Wooden groynes’ chief appeal is that they are smaller and more affordable to erect than many other groyne types. You may choose to go with either a one-row or two-row design with them. The one-row wooden groynes allow for some water to pass through, which can be beneficial if you’re concerned about the uneven accumulation of sediment between their two sides. Without some degree of penetrability, the side facing oncoming waves will collect sediment while the side that the groyne blocks off experiences more erosion. If you decide to make a two-row wooden groyne, you can expect that it will be sturdier and allow far less water to move through it. Either way, though, wooden groynes don’t have much longevity and are prone to decomposing from the water and the substances dissolved in it. A potential solution to this would be to use plastic wood instead of regular wood. You can handle and cut plastic wood in the same way as normal wood, but it will not rot or discolor. Moreover, plastic wood can include fiberglass reinforcements that make it tougher than regular wood.
Steel Groynes: Steel groynes may come in various appearances because you can construct them from contiguous sheet piling or use standalone piles that resemble those of wooden groynes. Because they generally don’t have gaps, they don’t let any water or sediment pass along their length. While steel seems like a strong material, it is rather fragile in aqueous environments. The small sand particles that move around a groyne can wear steel down quickly, and the water and the solutes that it contains cause rusting and decay. Steel’s vulnerabilities make it inapt for groyne composition in most cases. It is usually much more effective as a reinforcement for concrete since the two materials cover each other’s weaknesses. The concrete removes direct water contact from the steel, while the steel makes the concrete more hard-wearing, as stated above.
Rubble-Mound Groynes: Similar to stone groynes, rubble-mound groynes are composed of loose, uneven pieces that builders bring together. However, their components can be a mixture of concrete and stone rubble, along with steel sheet piling. The concrete and rocks cover the steel to form a mutually beneficial relationship in the same vein as reinforced concrete groynes. Furthermore, rubble-mound groynes are larger and wider when compared to wooden or steel groynes. This imparts rubble-mound groynes with great robustness. Their design also allows them to absorb the impacts of waves efficiently. In terms of appearances, their rugged nature allows for fewer maintenance needs, as they are already somewhat amorphous. Rubble-mound groynes’ strengths make them a common choice for people looking for a solution to sediment movement.
Sandbag Groynes: Using sandbags to make groynes is a temporary measure for stopping shoreline erosion. Unlike the other different types of groynes, you shouldn’t expect sandbag groynes to remain fully functional for more than about five years, at the most. They work as impermeable physical barriers that will stop water and sediment, though you do need to make some considerations for them to be effective. For one thing, the end of the groyne that is furthest from the land should have extra reinforcement to stand up to impacts. You must also think about the size and weight of each individual bag. Too light and they will readily become damaged or move when waves hit them. A good rule of thumb to follow with them is to choose bags that are more than fifty kilograms. Ultimately, sandbag groynes are not the best at dispersing wave energy, and they will break down quickly, leaving unattractive pieces of cloth and lumps of sand behind.
(3). Jetties: These are large massive groynes, which project into deeper water. They are used to protect the mouth of rivers for navigation. Jetties deflect the longshore currents to deeper water and stop the sediment outside the channel way. There are mainly two types of jetties; (i). Those constructed on the river mouth, (ii). Those constructed on the coastal entrance, which is used for the berthing of ships on harbors.