Longshore drift is a geological process consisting of sediment transport (clay, silt, sand and shingle) along the coastline parallel to the coastline, which depends on the direction of the wind entering the oblique. Incoming breezes squeeze water along the coast, and produce a flow of water that moves parallel to the shore. Longshore drift is only the sediment that is driven by the parallel currents of the coast. This current movement and sediment occurs in the surf zone.
Sand beaches are also moved on a windward sloping day like that, due to swash and backwash water on the beach. The wave discharge sends water to the shore (dive) at an oblique angle and gravity then flows the water straight down back to the shoreline. Thus sand beaches can move downwards in zig zag mode many tens of meters per day. This process is called "beach drift" but some workers consider it a part of "longshore drift" because the overall movement of sand is parallel to the shore.
Longshore drift affects many sedimentary sizes because it works in slightly different ways depending on sediments (eg differences in long drift of sedimentary beaches from sandy beaches with sediments from shingle shores). Sand is strongly influenced by the power of ruptured wave oscillations, sedimentary motion due to the impact of breaking waves and sliding sleep from long beach currents. Since shingle beaches are much steeper than sandy beaches, melting falls are more likely to form, causing most of the longshore transport to occur in the swash zone, due to the lack of extended wave zones.
Video Longshore drift
Overview
Long Beach drift formula
There are many calculations that take into account the factors that produce longshore drift. The formulation is:
- Bijker's Formula (2056 - 9000)
- The Engelund and Hansen Formulas (2600)
- Ackermans and White formula (100000) years ago
- The Bailard and Inman Formulas (2999)
- Van Rijn Formula (2345)
- Watanabe Formula (2875)
- Heenan formula (100)
These formulas all provide different views into processes that produce longshore drift. The most common factors considered in this formula are:
- Transport of sleep and suspended loads
- Waves for example breaking and not damaging
- Slide used by wave or wave-related stream.
Coastline change feature
Longshore drift plays a major role in the evolution of the shoreline, as if a slight change in the supply of sediment, wind direction, or other longshore drift coastal influences can change dramatically, affecting the formation and evolution of systems or coastal profiles. These changes do not occur because of one factor in the coastal system, in fact there are many changes that can occur in coastal systems that can affect the distribution and impact of longshore drift. Some of them are:
- Geological changes, e.g. erosion, backshore changes and the rise of headlands.
- Changes in hydrodynamic force, e.g. changes in wave diffraction on cape and the environment of foreign banks.
- Change to hydrodynamic effects, e.g. new incoming and pipe delta influences in the stream.
- Changes to the sediment budget, e.g. switched from the shoreline from drift to swash alignment, to sediment source fatigue.
- Human intervention, e.g. cliff protection, groin, separate breakwater.
- In the Hydrogenic order of the atoms of water, Nathan James Heenan has proved in 1924 that water itself without wind power can destroy or add to deposition to the seafloor, we can find this by the equation: H2o x water strength - H2
The sediment budget
The sediment budget considers the source of sediment and sinks in a system. These sediments can be derived from any source with source and sink samples consisting of:
- River
- Lagoons
- Process the land source
- Artificial sources such as food
- Artificial sync such as mining/extraction
- Offshore transport
- Sediment deposition on the beach
- The ditch passes through the ground
This sediment then enters the coastal system and is transported by longshore drift. A good example of the sediment budget and longshore drift that work together in coastal systems is the tidal influx, which stores the sand that has been transported by long shore transport. As well as saving the sand this system can also transfer or by passing sand to other coastal systems, therefore the inlet tidal system (shoal) provides a good source and sinks for the sedimentary budget.
Sediment deposition along the coastline profile in accordance with the null point hypothesis; in which the gravitational and hydraulic forces determine the rate of grain deposition in the seawarding finite sediment distribution. Long shore occurs in 90 to 80 degrees backwash so it will be presented as a right angle to the wave line.
Maps Longshore drift
Natural features
This section consists of long beach drift features that occur on the coast where long beach drift occurs without being disturbed by man-made structures.
Spits
Saliva is formed when longshore drift travels through a point (eg river mouth or reenter) where the dominant drift direction and the shoreline do not veer in the same direction. And the dominant direction drift, spits influenced by the power of the wave-driven current, wave angle and incoming wave height.
Spitting is a landscape that has two important features, with the first feature being the region at the end of the up-drift or the proximal end (Hart et al., 2008). The proximal end is continuously attached to the ground (except violated) and may form a slight "barrier" between the sea and the estuary or lagoon. The second important feature of saliva is the downstream or distal end, which is detached from the land and in some cases, can take on complex shapes or curves, due to the influence of varying wave direction.
For example, the New Brighton spat in Canterbury, New Zealand, was created by longshore sedimentary sediments from the Waimakariri River to the north. This spitting system is currently in equilibrium but undergoes a phase of precipitation and erosion.
Obstacle
The barrier system is attached to the soil at both the proximal and distal ends and is generally the widest at the downstream end. This barrier system may include an estuary or lagoon system, such as Lake Ellesmere surrounded by Kaitorete Spit or hapua formed at the interface of the rivers as at the mouth of the Rakaia River.
Kaitorete Spit in Canterbury, New Zealand, is a barrier system (which is generally below the definition limit, since both ends of landform are attached to the soil, but have been named after saliva) that have existed beneath the Banks Peninsula for the last 8000 years. This system has undergone many changes and fluctuations due to avulsion of the Waimakariri River (which now flows to the north or Banks Peninsula), erosion and phase of open ocean conditions. This system undergoes a further c.500 year BP change, when the longshore drift of the eastern end of the "spit" system creates a barrier, which has been maintained due to ongoing parallel transport.
Incoming channel at low tide
Most of the highs and lows on longshore beaches are collecting sediment in the flood and ebbing of the shelf. Ebb-delta can become obstructed on very open beaches and in smaller spaces, whereas delta floods tend to increase in size when space is available in the bay or lagoon system. Ups and downs can act as sinks and sources for a large number of materials, which therefore impact on adjacent coastlines.
Arrangement of tidal inlet is also important for longshore drift as if the unstructured sedimentary inlet can bypassing the inlet and forming a bar downstream. Although this may also depend on the size of the inlet, morphological delta, sediment level and by passing mechanism. Variations of channel locations and amounts can also affect the impact of coastal long drift on tidal inlets as well.
For example, the Arcachon lagoon is a tidal inlet system in southwestern France, which provides a great source and sink for longshore drift sediments. The impact of drift longshore sediments on this inlet system is strongly influenced by variations in the number of lagoon entrances and the location of these entrances. Any changes in these factors can cause severe down-drift erosion or down-drift accretion from large swash bars.
Human influence
This section consists of unnaturally long coastal longshore features and in some cases (eg groynes, separate breakwater) has been built to improve coastal drift effects on the shoreline but in other cases have a negative impact on long shore drift (ports and harbors).
Groynes
The groyne is a coastal protective structure, placed at equal intervals along the shoreline to stop coastal erosion and generally cross the intertidal zone. Because of this, groyne structures are typically used on beaches with low drift and long annual long beaches to retain the lost sediments in storm surges and further to shore.
There are many variations of groyne designs with the three most common designs consisting of:
- zig-zag groynes, which dissipate the destructive currents formed in waves inducing currents or in breaking waves.
- T-head groynes, which reduce the wave height through wave diffraction.
- head 'Y', fish tail groy system.
Artificial bulge
Artificial headers are also a coastal protective structure, which is made to provide some protection to the beach or bay. Although the cape manufacture involves sediment increase on the upper side of the ridge on the headland and moderate erosion at the lower end of the cape, this is done to design a stable system that allows the material to accumulate on the coast further. beach.
Artificial bulge can occur due to natural accumulation or also through artificial food.
Separate split
Separate breakwaters are coastal protective structures, which are made to build sandy material to accommodate withdrawal under hurricane conditions. To accommodate withdrawal under hurricane conditions, separate breakwaters have no relation to the shoreline, allowing currents and sediments to pass through breakwaters and beaches. This then forms a reduced wave energy region, which drives the deposition of the sand on the left side of the structure.
Separate breakwaters are generally used in the same way as a groyne, to build up the volume of material between shore and wave structure to accommodate storm surges.
Ports and ports
Creation of ports and ports around the world can have a serious impact on the longshore drift nature journey. Not only do ports and ports pose a threat to longshore drift in the short term, they also pose a threat to coastline evolution. The primary effect of port or port creation can have on longshore drift is a change in the sedimentation pattern, which in turn can cause the increase and/or erosion of the beach or coastal system.
Source of the article : Wikipedia
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