--- title: "Beach evolution" chunk: 2/5 source: "https://en.wikipedia.org/wiki/Beach_evolution" category: "reference" tags: "science, encyclopedia" date_saved: "2026-05-05T07:34:26.041541+00:00" instance: "kb-cron" --- Abandonment of shore: do nothing, let the natural process takeover. Managed retreat, also called realignment. Hold the shoreline: by using shoreline hardening techniques to create permanent concrete and rock constructions such as groynes. Move beach seaward: by using hard and soft intervention techniques usually in areas of high economic significance. Limited intervention: usually in areas of low economic significance, often includes the succession of haloseres, including salt marshes and sand dunes. === Coastal engineering === Coastal engineering techniques can be classified into two categories: hard engineering methods and soft engineering methods ==== Hard engineering methods ==== Hard engineering methods are also called "Structural methods". "Move towards the sea" beach accretion can be facilitated by the four main type of hard engineering structures, namely seawall, revetment, groyne or breakwater. Most commonly used hard structures are seawall and series of "headland groyne" (breakwater connected to the shore with groyne). ===== Main types of structures ===== Four main types of structures or accropodes are seawalls, groynes, breakwater and revetments. Headland groynes are a combination of breakwater and groyne. ====== Seawalls ====== Seawalls re-direct most of the incident energy in the form of sloping revetments, resulting in low reflected waves and much reduced turbulence. Designs use porous designs of rock or concrete objects such as Tetrapods or Xblocs with flights of steps for beach access. Seawall at Cronulla beach, NSW, for example, uses concrete wall. Submerged seawalls or structures are constructed to create the underwater reefs to slow down wave energy and beach erosion. ====== Groynes and Headland groyne ====== Groynes are the walls perpendicular to the coastline. Groynes are generally placed in series and the areas between groups of groynes are called groyne fields. To directs the sand towards the shore targeted for sand accumulation, a shorter groyne turned slightly towards downdrift side of the beach is deployed at updrift end of the beach, a longer groyne at the downdrift end of the beach is deployed, a series of groyne are deployed between the two ends. Groynes are often made of gabion, greenharts, concrete, rock or wood. Material builds up on the downdrift side, where littoral drift is predominantly in one direction, creating a wider and a more plentiful beach. Groynes are cost-effective, require little maintenance and are one of the most common defences. Headland groyne or Bulkhead breakwater When groyne is built to attach a breakwater to shore, the resulting T-structure is called "headland breakwater", "headland groyne", "bulkhead groyne" or "bulkhead breakwater". Use of groynes and headland groyne, accumulates the sand across the beach but it tend to deplete the sand faster from the downdrift end of the beach. This can be mitigated and sand could be accumulated at the downdrift end of the beach also. This is achieved by having a longer "groyne" or "headland groyne" at the end of downdrift side of the beach. To enhance the sand accumulation, this "headland groyne" could have another series of smaller "headland groyne" jutting out of it pointing towards updrift end of the beach in a way that the smaller "headland groyne" are parallel to the shore and perpendicular to main "headland groyne". This will facilitate gradual natural creation of ayre (sand or gravel filled beach). If there is a near shore island near the downdrift end of the beach and "headland groyne", then this could be turned into a cuspate foreland headland with the use of the gradual natural creation of ayre (gravel filled beach). Main "headland groyne" at the end of downdrift could be further stabilized by a hard engineered detention basin and grassy mangrove salt marsh. Salt marsh could be created with the use of soft engineering approach, such as lose stone sills, while leaving a whole in the sill for a seawater channel. Seawater channel could be a cemented open channel or a pipe buried under the beach. This marsh could be designed to taper into a hard engineered sandy beach. Having inland saltwater marsh between the beach and mainland will lower the cost by eliminating the need for filling up the marshy area with the sand, and the mangroves and grasses in the marsh will facilitate gradual built up of sediments. ====== Breakwater ====== Breakwater, also called "offshore breakwater", are offshore structure constructed parallel to the shore to alter wave direction and tide energy. The waves break further offshore and therefore lose erosive power. This leads to formation of wider beaches, which further absorb wave energy. A series of breakwaters is often deployed across the beach shore. ====== Revetment ====== Revetments are slanted or upright blockades, built parallel to the coast, usually towards the back of the beach to protect the area beyond. The most basic revetments consist of timber slants with a possible rock infill. Waves break against the revetments, which dissipate and absorb the energy. The shoreline is protected by the beach material held behind the barriers, as the revetments trap some of the material. Unless other methods are used in combination, surf progressively erodes and destroys the revetment which requires ongoing maintenance. ===== Other types of structures ===== ====== Riprap / Rock armour ====== Rock armour, also called riprap, is basement placed at the sea edge using local material. This could be the protruding foot of a seawall or revetment to reduce maintenance of those. Longshore drift is not hindered. ====== Cliff stabilization ====== Cliff stabilization can be accomplished through drainage of excess rainwater of through terracing, planting and wiring to hold cliffs in place. ====== Floodgates ====== Floodgates prevent damage from storm surges or any other type of natural disaster that could harm the area they protect. They are habitually open and allow free passage, but close under threat of a storm surge. The Thames Barrier is an example of such a structure. ===== Construction elements ===== These construction elements can be incorporated in any of the above structures, either as core element or as a supplementary element to enhance to reduce the cost and maintenance of main structural elements.