Coastal sediment transport

Coastal sediment transport (a subset of sediment transport) is the interaction of coastal land forms to various complex interactions of physical processes.[1][2] The primary agent in coastal sediment transport is wave activity (see Wind wave), followed by tides and storm surge (see Tide and Storm surge), and near shore currents (see Sea#Currents) .[1] Wind-generated waves play a key role in the transfer of energy from the open ocean to the coastlines.[1] In addition to the physical processes acting upon the shore, the size distribution of the sediment is a critical determination for how the beach will change (see Grain size determination). These various interactions generate a wide variety of beaches. (see Beach). Other than the interactions between coastal land forms and physical processes there is also the addition of modification of these landforms through anthropogenic sources (see human modifications). Some of the anthropogenic sources of modification have been put in place to halt erosion or prevent harbors from filling up with sediment.[2] In order to assist community planners, local governments, and national governments a variety of models have been developed to predict the changes of beach sediment transport at coastal locations. Typically, during large wave events, the sediment gets transported off the beach face a deposited offshore generating a sandbar. Once the significant wave event has diminished, the sediment then gets slowly transported back onshore.[3]

Assateague Island aerial view

History

In the mid-1970s a significant amount of attention was paid to coastal sediment transport. In part, due to the National Sea Grant College Program and the U.S. Congress Mandated Sea Grant Act of 1976. One of the research areas included "the development and the experimental verification of hydrodynamic laws governing the transport of marine sediments in the flow fields occurring in coastal waters." [4] From this request for research, the Office of Sea Grant reviewed, accepted, and funded the Nearshore Sediment Transport Study (NSTS). Due to unforeseen complications the NSTS conducted only two major field experiments and a validation experiment.[4] This was a significant contribution to the field of coastal sediment transport and helped initialize a great deal of future research.

Glossary

shore 
zone between the water's edge at normal low tide and the landward limit of effective wave action.[2]
shoreline 
the water's edge, migrating up and down with the tide.[2]
foreshore 
exposed at low tide and submerged at high tide.
backshore 
extending above normal high tide level.
nearshore zone 
between shoreline and the line where the waves begin to break.[2]
beach 
an accumulation of loose sediment sometimes confined to the backshore but often extending across the foreshore as well.

Beach profile measurements

A variety of measurements are used to determine the beach profile, sediment grain size, and various other important parameters to determine what is influencing coastal sediment transport. Below are a few of the multitude.

Coastal research amphibious buggy (CRAB)

A three-wheeled vehicle deployed at the beach to measure the beach profile. (more information can be found at http://frf.usace.army.mil/vehicles2.stm)

Emory beach profile measurement

Method for collecting beach sediment and beach profile
A simple depiction of measuring a beach profile and compiling a median grain size.

In order to determine what the profile of a beach looks like, one method for determination is the Emory Beach Profiling Method. Initiating a benchmark, the researcher establishes a control point to start the surveys at. Typically this is far enough away from the swash zone that large changes in elevation will not occur during the sampling time. Once the initial benchmark is established, the researcher will take the Emory sampling device and measure the change in elevation over the distance the device is covering. Then, they will pick up the device and move it to the end point of their last survey, and so on. Until they reach the shoreline. Typically this is done during neap tide (see Tide for more information on neap tide).

Grain size determination

Since the sand grain diameters can vary throughout the entire beach the median grain size is used to determine sediment fall velocity. Determining sediment fall velocity allows the determination of what sediment is left where...[3]

Bay D 50 Prob Curve
probability curve for beach face sediment distribution, how to obtain D50

Human modifications

  • Sea walls
  • Groynes
  • Breakwaters
  • Dredging of harbor entrances
  • Dumping of material on the coast and offshore
  • Reduction of coastal vegetation (cutting, burning, grazing, pollution)

Models

Models for the prediction of sediment transport in coastal regions have been used since the mid 1970s.[4] Some transport models are:

References

  1. ^ a b c Komar, Paul D. Crc Handbook of Coastal Processes and Erosion. Crc Series in Marine Science. Boca Raton, Fla.: CRC Press, 1983. Print.
  2. ^ a b c d e Bird, E. C. F. Coasts. An Introduction to Systematic Geomorphology,. Cambridge, Mass.,: M.I.T. Press, 1969. Print.
  3. ^ a b Dean, Robert G., and Robert A. Dalrymple. Coastal Processes : With Engineering Applications. Cambridge, UK New York: Cambridge University Press, 2002. Print.
  4. ^ a b c Seymour, Richard J. Nearshore Sediment Transport. New York ; London: Plenum Press, 1989. Print.
  5. ^ Dalrymple, R.A., Prediction of Storm/Normal Beach Profiles, Journal of Waterway, Port, Coastal, and Ocean Engineering, ASCE, 118, 2, 193-200, 1992.
Coastal management

Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands.Coastal zones occupy less than 15% of the Earth's land area, while they host more than 45% of the world population. Nearly 1.4 billion people live within 100 km of a shoreline and 100 m of sea level, with an average density 3 times higher than the global average for population. With three-quarters of the world population expected to reside in the coastal zone by 2025, human activities originating from this small land area will impose heavy pressure on coasts. Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities.

Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates. Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy.

DHI (company)

DHI, previously known as DHI - Institut for Vand og Miljø (DHI – Institute for Water and Environment), is an international software development and engineering consultant firm headquartered in Denmark which specializes in hydraulic and hydrological modeling software. Originating in an institute founded in 1964, DHI has about 30 offices throughout the world, with software development centres in Singapore and Hørsholm, Denmark, and approximately 1100 employees.

DHI takes its name from the acronym of the Dansk Hydraulisk Institut (Danish Hydraulic Institute), which was founded in 1964 by the Technical University of Denmark as Vandbygningsinstituttet (The Institute of Water Production) and changed its name in 1971; DHI - Institut for Vand og Miljø was formed in 2000 by the merger of that with Vandkvalitetsinstituttet (The Institute for Water Quality), and in 2005 further merged with the Dansk Toksikologi Center (Danish Toxicology Centre) and simplified its name to DHI.While independent, DHI is associated with the Danish Academy of Technical Sciences and maintains a partnership with the United Nations Environment Programme focused on management of water resources. DHI's 2015 corporate revenue was about €119.5M. Its headquarters are in Hørsholm; another centre is in Singapore. Among its recent consulting projects as of 2016 are a study of the causes of the 2011 flooding in Grantham, Queensland, Australia, an analysis of five Himalayan rivers as part of the Uttarakhand Disaster Recovery Project and research on effects of planned dams on the River Mekong.

Journal of Geophysical Research

The Journal of Geophysical Research is a peer-reviewed scientific journal. It is the flagship journal of the American Geophysical Union. It contains original research on the physical, chemical, and biological processes that contribute to the understanding of the Earth, Sun, and solar system. It has seven sections: A (Space Physics), B (Solid Earth), C (Oceans), D (Atmospheres), E (Planets), F (Earth Surface), and G (Biogeosciences). All current and back issues are available online for subscribers.

Kaikoura Peninsula

The Kaikoura Peninsula is located in the northeast of New Zealand's South Island. It protrudes five kilometres into the Pacific Ocean. The town of Kaikoura is located on the north shore of the peninsula. The peninsula has been settled by Maori for approximately 1000 years, and by Europeans since the 1800s, when whaling operations began off the Kaikoura Coast. Since the end of whaling in 1922 whales have been allowed to thrive and the region is now a popular whale watching destination.

The Kaikoura Peninsula is made up of limestone and mudstone which have been deposited, uplifted and deformed throughout the Quaternary. The peninsula is situated in a tectonically active region bounded by the Marlborough Fault System.

The Kaikoura Canyon is a submarine canyon situated 500 metres off the coast to the south-east of the peninsula. It is 60 km long, up to 1200 m deep, and is generally U-shaped. It is an active canyon that merges into a deep-ocean channel system that meanders for hundreds of kilometres across the deep ocean floor.

Miracle Beach Provincial Park

Miracle Beach Provincial Park is a provincial park on the eastern shore of Vancouver Island in British Columbia, Canada. Located between Comox and Campbell River, the park includes a foreshore area in the Strait of Georgia, much of the Black Creek estuary, and a forested area. According to its Master Plan, it fulfills primarily a recreational role with a focus on beach play, picnicking, nature appreciation, and camping, and a secondary conservation role with a focus on the natural shoreline and estuary. I support of its recreational focus the park is developed with a day-use parking area with accessible trails leading to the shoreline and a camping area with 200 drive-in sites. The park is also hosts a nature centre building and a sheltered group picnic shelter. Vegetation in the park is typical for the region's second-growth forests with Douglas-fir most prominent. Common associates include Western hemlock, Sitka spruce, red alder and bigleaf maple. Salal and sword fern are the most abundant shrub. Black Creek, which flows through the park, is a spawning area for coho salmon.

Sediment transport

Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural systems where the particles are clastic rocks (sand, gravel, boulders, etc.), mud, or clay; the fluid is air, water, or ice; and the force of gravity acts to move the particles along the sloping surface on which they are resting. Sediment transport due to fluid motion occurs in rivers, oceans, lakes, seas, and other bodies of water due to currents and tides. Transport is also caused by glaciers as they flow, and on terrestrial surfaces under the influence of wind. Sediment transport due only to gravity can occur on sloping surfaces in general, including hillslopes, scarps, cliffs, and the continental shelf—continental slope boundary.

Sediment transport is important in the fields of sedimentary geology, geomorphology, civil engineering and environmental engineering (see applications, below). Knowledge of sediment transport is most often used to determine whether erosion or deposition will occur, the magnitude of this erosion or deposition, and the time and distance over which it will occur.

Water
Glacial
Hillslope
Aeolian

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