5.4 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Longshore drift | 3/3 | https://en.wikipedia.org/wiki/Longshore_drift | reference | science, encyclopedia | 2026-05-05T07:35:20.233864+00:00 | kb-cron |
Groynes are shore protection structures, placed at equal intervals along the coastline in order to stop coastal erosion and generally cross the intertidal zone. Due to this, groyne structures are usually used on shores with low net and high annual longshore drift in order to retain the sediments lost in storm surges and further down the coast. There are numerous variations to groyne designs with the three most common designs consisting of:
zig-zag groynes, which dissipate the destructive flows that form in wave-induced currents or in breaking waves. T-head groynes, which reduce wave height through wave diffraction. ‘Y’ head, a fish-tail groyne system.
=== Artificial headlands === Artificial headlands are also shore protection structures, which are created in order to provide a certain amount of protection to beaches or bays. Although the creation of headlands involves accretion of sediments on the up-drift side of the headland and moderate erosion of the down-drift end of the headland, this is undertaken in order to design a stabilised system that allows material to accumulate in beaches further along the shore. Artificial headlands can occur due to natural accumulation or also through artificial nourishment.
=== Detached breakwaters === Detached breakwaters are shore protection structures, created to build up sandy material in order to accommodate drawdown in storm conditions. In order to accommodate drawdown in storm conditions detached breakwaters have no connection to the shoreline, which lets currents and sediment pass between the breakwater and the shore. This then forms a region of reduced wave energy, which encourages the deposition of sand on the lee side of the structure. Detached breakwaters are generally used in the same way as groynes, to build up the volume of material between the coast and the breakwater structure in order to accommodate storm surges.
=== Ports and harbours === The creation of ports and harbours throughout the world can seriously impact on the natural course of longshore drift. Not only do ports and harbours pose a threat to longshore drift in the short term, they also pose a threat to shoreline evolution. The major influence, which the creation of a port or harbour can have on longshore drift, is the alteration of sedimentation patterns, which in turn may lead to accretion and/or erosion of a beach or coastal system. As an example, the creation of a port in Timaru, New Zealand in the late 19th century led to a significant change in the longshore drift along the South Canterbury coastline. Instead of longshore drift transporting sediment north up the coast towards the Waimataitai lagoon, the creation of the port blocked the drift of these (coarse) sediments and instead caused them to accrete to the south of the port at South beach in Timaru. The accretion of this sediment to the south, therefore meant a lack of sediment being deposited on the coast near the Waimataitai lagoon (to the north of the port), which led to the loss of the barrier enclosing the lagoon in the 1930s and then shortly after, the loss of the lagoon itself. As with the Waimataitai lagoon, the Washdyke Lagoon, which currently lies to the north of the Timaru port, is undergoing erosion and may eventually breach, causing loss of another lagoon environment.
== See also == Beach evolution Beach erosion and accretion Coastal management, to prevent coastal erosion and creation of beach Coastal erosion Coastal geography Sand dune stabilisation
== References ==
=== Citations ===
=== Books === Bruun, Per, ed. (2005). Port and coastal engineering developments in Science and technology. South Carolina: P. Bruun. Hart, D.E; Marsden, I; Francis, M (2008). "Chapter 20: Coastal systems". In Winterbourne, M; Knox, G.A.; Marsden, I.D.; Burrows, C (eds.). Natural history of Canterbury (3rd ed.). Canterbury University Press. pp. 653–684. Reeve, D; Chadwick, A; Fleming, C (2004). Coastal engineering-processes, theory and design practice. New York: Spon Press.
=== Journal articles === Kirk, R.M; Lauder, G.A (2000). "Significant coastal lagoon systems in the South Island, New Zealand". Science for Conservation. DOC 46p: 13–24. Michel, D; Howa, H.L (1997). "Morphodynamic behaviour of a tidal inlet system in a mixed-energy environment". Physics and Chemistry of the Earth. 22 (3–4): 339–343. Bibcode:1997PCE....22..339M. doi:10.1016/s0079-1946(97)00155-9. Peterson, D; Deigaard, R; Fredsoe, J (July 2008). "Modelling the morphology of sandy spits". Coastal Engineering. 55 (7–8): 671–684. Bibcode:2008CoasE..55..671P. doi:10.1016/j.coastaleng.2007.11.009. Soons, J.M; Schulmeister, J; Holt, S (April 1997). "The Holocene evolution of a well nourished gravelly barrier and lagoon complex, Kaitorete "Spit", Canterbury, New Zealand". Marine Geology. 26 (1–2): 69–90. Bibcode:1997MGeol.138...69S. doi:10.1016/S0025-3227(97)00003-0.
== External links == Photos, animation and explanation for schools, geography-site.co.uk Intranet.lissjunior.hants.sch.uk has a brief animation on longshore drift. USGS — Coastal Erosion on Cape Cod, woodshole.er.usgs.gov Shore drift, ecy.wa.gov Longshore drift in South Carolina, cofc.edu British Geological Survey: portable streamer traps for longshore sediment transport measurement