Editing Beach (section)

==Erosion and accretion==
{{unsourced section|date=April 2025}}
===Natural erosion and accretion===
[[File:Mekong_beach_in_Si_Phan_Don.jpg|thumb|A [[Spit (landform)|sandspit]] can form if a beach suddenly changes direction.]]
[[File:Hidden Beach (15093910956).jpg|thumb|Hidden beach in southern [[Croatia]]]]
[[File:Porto Covo July 2011-1.jpg|thumb|Playing in the surf is a popular recreational activity.]]
[[File:The beach at North Seymour Island in the Galapagos.jpeg|thumb|Beach in the [[Galápagos Islands]] reserved for marine animals]]
[[File:Anse Source d'Argent beach aerial La Digue, Seychellen (39587432402).jpg|thumb|Anse Source d'Argent, [[La Digue]], [[Seychelles]]]]
[[File:Malediven Wasserbungalow (28800500816).jpg|thumb|Maldives dream beaches]]

====Causes====

Beaches are changed in shape chiefly by the movement of water and wind.  Any weather event that is associated with turbid or fast-flowing water or high winds will erode exposed beaches. Longshore currents will tend to replenish beach sediments and repair storm damage.  Tidal waterways generally change the shape of their adjacent beaches by small degrees with every tidal cycle.  Over time these changes can become substantial leading to significant changes in the size and location of the beach.

====Effects on flora====
Changes in the shape of the beach may undermine the roots of large trees and other flora. Many beach adapted species (such as coconut palms) have a fine root system and large root ball which tends to withstand wave and wind action and tends to stabilize beaches better than other trees with a lesser root ball.

====Effects on adjacent land====
Erosion of beaches can expose less resilient soils and rocks to wind and wave action leading to undermining of coastal headlands eventually resulting in catastrophic collapse of large quantities of overburden into the shallows.  This material may be distributed along the beach front leading to a change in the habitat as sea grasses and corals in the shallows may be buried or deprived of light and nutrients.

===Humanmade erosion and accretion===
Coastal areas settled by man inevitably become subject to the effects of human-made structures and processes. Over long periods of time, these influences may substantially alter the shape of the coastline, and the character of the beach.

====Destruction of flora====
Beachfront flora plays a major role in stabilizing the foredunes and preventing beach head erosion and inland movement of dunes.  If flora with network root systems (creepers, grasses, and palms) are able to become established, they provide an effective coastal defense as they trap sand particles and rainwater and enrich the surface layer of the dunes, allowing other plant species to become established.  They also protect the berm from erosion by high winds, freak waves and subsiding floodwaters.

Over long periods of time, well-stabilized foreshore areas will tend to accrete, while unstabilized foreshores will tend to erode, leading to substantial changes in the shape of the coastline.  These changes usually occur over periods of many years. Freak wave events such as tsunami, tidal waves, and storm surges may substantially alter the shape, profile and location of a beach within hours.

Destruction of flora on the berm by the use of herbicides, excessive pedestrian or vehicle traffic, or disruption to freshwater flows may lead to erosion of the berm and dunes.  While the destruction of flora may be a gradual process that is imperceptible to regular beach users, it often becomes immediately apparent after storms associated with high winds and freak wave events that can rapidly move large volumes of exposed and unstable sand, depositing them further inland, or carrying them out into the permanent water forming offshore bars, lagoons or increasing the area of the beach exposed at low tide.
Large and rapid movements of exposed sand can bury and smother flora in adjacent areas, aggravating the loss of habitat for fauna, and enlarging the area of instability. If there is an adequate supply of sand, and weather conditions do not allow vegetation to recover and stabilize the sediment, wind-blown sand can continue to advance, engulfing and permanently altering downwind landscapes.

Sediment moved by waves or receding floodwaters can be deposited in coastal shallows, engulfing reed beds and changing the character of underwater flora and fauna in the coastal shallows.

Burning or clearance of vegetation on the land adjacent to the beach head, for farming and residential development, changes the surface wind patterns, and exposes the surface of the beach to wind erosion.

Farming and residential development are also commonly associated with changes in local surface water flows. If these flows are concentrated in stormwater drains emptying onto the beach head, they may erode the beach creating a lagoon or delta.

Dense vegetation tends to absorb rainfall reducing the speed of runoff and releasing it over longer periods of time.  Destruction by burning or clearance of the natural vegetation tends to increase the speed and erosive power of runoff from rainfall.  This runoff will tend to carry more silt and organic matter from the land onto the beach and into the sea. If the flow is constant, runoff from cleared land arriving at the beach head will tend to deposit this material into the sand changing its color, odor and fauna.

====Creation of beach access points====
The concentration of pedestrian and vehicular traffic accessing the beach for recreational purposes may cause increased erosion at the access points if measures are not taken to stabilize the beach surface above high-water mark. Recognition of the dangers of loss of beach front flora has caused many local authorities responsible for managing coastal areas to restrict beach access points by physical structures or legal sanctions, and fence off foredunes in an effort to protect the flora.  These measures are often associated with the construction of structures at these access points to allow traffic to pass over or through the dunes without causing further damage.

====Concentration of runoff====
[[File:Alimini Otranto.jpg|thumb|Beach in [[Otranto]], [[Salento]], [[Apulia]], Italy]]
Beaches provide a filter for runoff from the coastal plain.  If the runoff is naturally dispersed along the beach, water borne silt and organic matter will be retained on the land and will feed the flora in the coastal area.  Runoff that is dispersed along the beach will tend to percolate through the beach and may emerge from the beach at low tide.

The retention of the freshwater may also help to maintain underground water reserves and will resist salt water incursion.  If the surface flow of the runoff is diverted and concentrated by drains that create constant flows over the beach above the sea or river level, the beach will be eroded and ultimately form an inlet unless longshore flows deposit sediments to repair the breach.

Once eroded, an inlet may allow tidal inflows of salt water to pollute areas inland from the beach and may also affect the quality of underground water supplies and the height of the water table.

====Deprivation of runoff====
Some flora naturally occurring on the beach head requires freshwater runoff from the land.  Diversion of freshwater runoff into drains may deprive these plants of their water supplies and allow sea water incursion, increasing the saltiness of the groundwater.  Species that are not able to survive in salt water may die and be replaced by mangroves or other species adapted to salty environments.

====Inappropriate beach nourishment====
Beach nourishment is the importing and deposition of sand or other sediments in an effort to restore a beach that has been damaged by erosion.  Beach nourishment often involves excavation of sediments from riverbeds or sand quarries.  This excavated sediment may be substantially different in size and appearance to the naturally occurring beach sand.

In extreme cases, beach nourishment may involve placement of large pebbles or rocks in an effort to permanently restore a shoreline subject to constant erosion and loss of foreshore.  This is often required where the flow of new sediment caused by the longshore current has been disrupted by construction of harbors, breakwaters, causeways or boat ramps, creating new current flows that scour the sand from behind these structures and deprive the beach of restorative sediments. If the causes of the erosion are not addressed, beach nourishment can become a necessary and permanent feature of beach maintenance.

During beach nourishment activities, care must be taken to place new sediments so that the new sediments compact and stabilize before aggressive wave or wind action can erode them. Material that is concentrated too far down the beach may form a temporary groyne that will encourage scouring behind it. Sediments that are too fine or too light may be eroded before they have compacted or been integrated into the established vegetation. Foreign unwashed sediments may introduce flora or fauna that are not usually found in that locality.

Brighton Beach, on the south coast of England, is a shingle beach that has been nourished with very large pebbles in an effort to withstand the erosion of the upper area of the beach.  These large pebbles made the beach unwelcoming for pedestrians for a period of time until natural processes integrated the naturally occurring shingle into the pebble base.