1.
Backwashing (water treatment)
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Backwashing is a form of preventive maintenance so that the filter media can be reused. In water treatment plants, backwashing can be a process that is run by local programmable logic controllers. Water treatment filters that can be backwashed include rapid sand filters, pressure filters, diatomaceous earth filters are backwashed according to the proprietary arrangement of pumps, valves and filters associated with the filtration system. Slow sand filters and self-cleaning screen filters employ mechanisms other than backwashing to remove trapped particles, to keep water treatment filters functional, they have to be cleaned periodically to remove particulates. Ineffective backwashing is one of the reasons that water treatment filters fail. Backwashing of granular media filters involves several steps, first, the filter is taken off line and the water is drained to a level that is above the surface of the filter bed. Next, compressed air is pushed up through the filter material causing the bed to expand breaking up the compacted filter bed. In some applications, air and water streams are simultaneously pushed upwards through the media followed by a rinse water wash. Backwashing continues for a time, or until the turbidity of the backwash water is below an established value. At the end of the cycle, the upward flow of water is terminated. Water to be filtered is then applied to the surface until the filter clogs. Some water treatment filters use surface wash systems that break up the heavily clogged, surface wash systems are buried in the top of the filter media or are suspended above the filter media surface. John R. Baylis developed a grid system which consisted of pipes with nozzles that injected jets of water into the filter material during expansion. Rotating arms use jets of water to break up the clogged filter surface, a surface wash step in a backwash cycle usually takes place at the beginning of the filter bed cleaning process. Spent backwash water is discharged without treatment to a sanitary sewer system or is treated and recycled within the plant. Historically, backwash water was discharged directly to water supplies, however. Used backwash water contains high concentrations of particulate material, typical treatment processes include coagulation, flocculation and sedimentation. High molecular weight synthetic polymers are sometimes added to facilitate the formation of settleable floc
2.
Geography
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Geography is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. The first person to use the word γεωγραφία was Eratosthenes, Geography is an all-encompassing discipline that seeks an understanding of the Earth and its human and natural complexities—not merely where objects are, but how they have changed and come to be. It is often defined in terms of the two branches of geography and physical geography. Geography has been called the world discipline and the bridge between the human and the physical sciences, Geography is a systematic study of the Earth and its features. Traditionally, geography has been associated with cartography and place names, although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the space and the temporal database distribution of phenomena, processes, because space and place affect a variety of topics, such as economics, health, climate, plants and animals, geography is highly interdisciplinary. The interdisciplinary nature of the approach depends on an attentiveness to the relationship between physical and human phenomena and its spatial patterns. Names of places. are not geography. know by heart a whole gazetteer full of them would not, in itself and this is a description of the world—that is Geography. In a word Geography is a Science—a thing not of mere names but of argument and reason, of cause, just as all phenomena exist in time and thus have a history, they also exist in space and have a geography. Geography as a discipline can be split broadly into two main fields, human geography and physical geography. The former largely focuses on the environment and how humans create, view, manage. The latter examines the environment, and how organisms, climate, soil, water. The difference between these led to a third field, environmental geography, which combines physical and human geography. Physical geography focuses on geography as an Earth science and it aims to understand the physical problems and the issues of lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns. Physical geography can be divided into broad categories, including, Human geography is a branch of geography that focuses on the study of patterns. It encompasses the human, political, cultural, social, and it requires an understanding of the traditional aspects of physical and human geography, as well as the ways that human societies conceptualize the environment. Integrated geography has emerged as a bridge between the human and the geography, as a result of the increasing specialisation of the two sub-fields. Examples of areas of research in the environmental geography include, emergency management, environmental management, sustainability, geomatics is concerned with the application of computers to the traditional spatial techniques used in cartography and topography
3.
Wind wave
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In fluid dynamics, wind waves, or wind-generated waves, are surface waves that occur on the free surface of bodies of water. They result from the wind blowing over an area of fluid surface, Waves in the oceans can travel thousands of miles before reaching land. Wind waves on Earth range in size from small ripples, to waves over 100 ft high, when directly generated and affected by local winds, a wind wave system is called a wind sea. After the wind ceases to blow, wind waves are called swells, more generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time. They have been generated elsewhere or some time ago, wind waves in the ocean are called ocean surface waves. Wind waves have an amount of randomness, subsequent waves differ in height, duration. The key statistics of wind waves in evolving sea states can be predicted with wind wave models, although waves are usually considered in the water seas of Earth, the hydrocarbon seas of Titan may also have wind-driven waves. The great majority of large breakers seen at a result from distant winds. Water depth All of these work together to determine the size of wind waves. Further exposure to that wind could only cause a dissipation of energy due to the breaking of wave tops. Waves in an area typically have a range of heights. For weather reporting and for analysis of wind wave statistics. This figure represents an average height of the highest one-third of the waves in a time period. The significant wave height is also the value a trained observer would estimate from visual observation of a sea state, given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for a particular day or storm. Wave formation on a flat water surface by wind is started by a random distribution of normal pressure of turbulent wind flow over the water. This pressure fluctuation produces normal and tangential stresses in the surface water and it is assumed that, The water is originally at rest. There is a distribution of normal pressure to the water surface from the turbulent wind. Correlations between air and water motions are neglected, the second mechanism involves wind shear forces on the water surface
4.
Longshore drift
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Longshore drift is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, which is dependent on oblique incoming wind direction. Oblique incoming wind squeezes water along the coast, and so generates a current which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore current and this current and sediment movement occurs within the surf zone. Beach sand is moved on such oblique wind days, due to the swash and backwash of water on the beach. Breaking surf sends water up the beach at an oblique angle, thus beach sand can move downbeach in a zig zag fashion many tens of meters per day. This process is called beach drift but some regard it as simply part of longshore drift because of the overall movement of sand parallel to the coast. Longshore drift affects numerous sediment sizes as it works in different ways depending on the sediment. Sand is largely affected by the force of breaking waves. There are numerous calculations that take into consideration the factors that produce longshore drift, some of these are, Geological changes, e. g. erosion, backshore changes and emergence of headlands. Change in hydrodynamic forces, e. g. change in wave diffraction in headland, change to hydrodynamic influences, e. g. the influence of new tidal inlets and deltas on drift. Alterations of the sediment budget, e. g. switch of shorelines from drift to swash alignment, the intervention of humans, e. g. cliff protection, groynes, detached breakwaters. The sediment budget takes into consideration sediment sources and sinks within a system, a good example of the sediment budget and longshore drift working together in the coastal system is inlet ebb-tidal shoals, which store sand that has been transported by long shore transport. As well as storing sand these systems may also transfer or by pass sand into other systems, therefore inlet ebb-tidal systems provide a good sources. Long shore occurs in a 90 to 80 degree backwash so it would be presented as an angle with the wave line. This section consists of features of long shore drift that occur on a coast where long shore drift occurs uninterrupted by man-made structures, spits are formed when longshore drift travels past a point where the dominant drift direction and shoreline do not veer in the same direction. As well as dominant drift direction, spits are affected by the strength of wave driven current, wave angle, spits are landforms that have two important features, with the first feature being the region at the up-drift end or proximal end. The proximal end is attached to land and may form a slight “barrier” between the sea and an estuary or lagoon. As an example, the New Brighton spit in Canterbury, New Zealand, was created by longshore drift of sediment from the Waimakariri River to the north and this spit system is currently in equilibrium but undergoes phases of deposition and erosion
5.
Sediment transport
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Sediment transport is the movement of solid particles, 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 due to fluid motion occurs in rivers, oceans, lakes, seas, 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, sediment transport is important in the fields of sedimentary geology, geomorphology, civil engineering and environmental engineering. Aeolian or eolian is the term for sediment transport by wind and this process results in the formation of ripples and sand dunes. Typically, the size of the sediment is fine sand and smaller, because air is a fluid with low density and viscosity. Bedforms are generated by aeolian sediment transport in the terrestrial near-surface environment, ripples and dunes form as a natural self-organizing response to sediment transport. Aeolian sediment transport is common on beaches and in the regions of the world, because it is in these environments that vegetation does not prevent the presence. Wind-blown very fine-grained dust is capable of entering the upper atmosphere, dust from the Sahara deposits on the Canary Islands and islands in the Caribbean, and dust from the Gobi desert has deposited on the western United States. This sediment is important to the budget and ecology of several islands. Deposits of fine-grained wind-blown glacial sediment are called loess, in geology, physical geography, and sediment transport, fluvial processes relate to flowing water in natural systems. This encompasses rivers, streams, periglacial flows, flash floods, sediment moved by water can be larger than sediment moved by air because water has both a higher density and viscosity. In typical rivers the largest carried sediment is of sand and gravel size, coastal sediment transport takes place in near-shore environments due to the motions of waves and currents. At the mouths of rivers, coastal sediment and fluvial sediment transport processes mesh to create river deltas, coastal sediment transport results in the formation of characteristic coastal landforms such as beaches, barrier islands, and capes. As glaciers move over their beds, they entrain and move material of all sizes, glaciers can carry the largest sediment, and areas of glacial deposition often contain a large number of glacial erratics, many of which are several metres in diameter. Glaciers also pulverize rock into glacial flour, which is so fine that it is carried away by winds to create loess deposits thousands of kilometres afield. Sediment entrained in glaciers often moves approximately along the glacial flowlines, in hillslope sediment transport, a variety of processes move regolith downslope. For this reason, the tops of hills generally have a parabolic concave-up profile, as hillslopes steepen, however, they become more prone to episodic landslides and other mass wasting events. Large masses of material are moved in debris flows, hyperconcentrated mixtures of mud, clasts that range up to boulder-size, debris flows move as granular flows down steep mountain valleys and washes
6.
Surf zone
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As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone, after breaking in the surf zone, the waves continue to move in, and they run up onto the sloping front of the beach, forming an uprush of water called swash. The water then runs back again as backswash, the nearshore zone where wave water comes onto the beach is the surf zone. The water in the zone, or breaker zone, is shallow. The animals that often are living in the surf zone are crabs, clams. Surf clams and mole crabs are two species that stand out as inhabitants of the surf zone, both of these animals are very fast burrowers. The surf clam, also known as the variable coquina, is a feeder that uses its gills to filter microalgae, tiny zooplankton. The mole crab is a feeder that eats by capturing zooplankton with its antennae. All of these creatures burrow down into the sand to escape from being pulled into the ocean from the tides and waves and they also burrow themselves in the sand to protect themselves from predators. The surf zone is full of nutrients, oxygen, and sunlight which leaves the very productive with animal life. The surf zone can contain dangerous rip currents, strong currents which flow offshore. Know how to swim and heed the advice of lifeguards, moderate-risk rip currents, Wind and/or wave conditions support stronger or more frequent rip currents. Only experienced surf swimmers should enter the water, high-risk rip currents, Wind and/or wave conditions support dangerous rip currents. Rip currents are life-threatening to anyone entering the surf, intertidal zone Littoral zone Surf fishing Pinet, Paul R Invitation to Oceanography, Chapter 11, The Dynamic Shoreline. Jones & Bartlett Learning, ISBN 0-7637-5993-7 Breaker Zone, metEd Rip currents, Nearshore fundamentals University Corporation for Atmospheric Research
7.
Water table
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The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water, the water table is the surface where the water pressure head is equal to the atmospheric pressure. It may be visualized as the surface of the materials that are saturated with groundwater in a given vicinity. The groundwater may be from precipitation or from groundwater flowing into the aquifer, in areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths water fills in more of the spaces in the soils. Below the water table, in the zone, layers of permeable rock that yield groundwater are called aquifers. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table should not be confused with the water level in a deeper well. The elevation of the water in this well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface. The water table may vary due to changes such as precipitation and evapotranspiration. Springs, rivers, lakes and oases occur when the table reaches the surface. Springs commonly form on hillsides, where the Earths slanting surface may intersect with the water table, Groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies. Within an aquifer, the table is rarely horizontal, but reflects the surface relief due to the capillary effect in soils, sediments. In the aquifer, groundwater flows from points of pressure to points of lower pressure. The slope of the table is known as the hydraulic gradient, which depends on the rate at which water is added to and removed from the aquifer. This occurs when there is a layer of rock or sediment or relatively impermeable layer above the main water table/aquifer. If a perched aquifers flow intersects the Earths dry surface, at a wall for example. On low-lying oceanic islands with porous soil, freshwater tends to collect in lenticular pools on top of the denser seawater intruding from the sides of the islands, such an islands freshwater lens, and thus the water table, rises and falls with the tides. In some regions, for example, Great Britain or California, winter precipitation is higher than summer precipitation
8.
Beach cusps
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Beach cusps are shoreline formations made up of various grades of sediment in an arc pattern. The horns are made up of material and the embayment contains finer sediment. They can be all over the world and are most noticeable on shorelines with coarser sediment such as pebble beaches. However, they can occur with sediment of any size and they nearly always occur in a regular pattern with cusps of equal size and spacing appearing along stretches of the shoreline. These cusps are most often a few metres long, however, they may reach 60 m across. Although the origin of beach cusps has yet to be proven and this is because when an oncoming wave hits the horn of a beach cusp, it is split and forced into two directions. The crashing of the wave into the cusps slows its velocity, causing sediment to fall out of suspension. The waves then flow along the embayments and run into one another in the middle, after this collision these waves attempt to flow back out to sea where they are met by incoming waves. Therefore, once the cusp is established, coarser sediment is constantly being deposited on the horn and this process causes the horns and embayments to at least maintain their size, if not grow larger. There are a number of theories as to why beach cusps are formed but currently, the regular arrival of incoming waves in the near shore waters causes the development of waves perpendicular to the direction of the incoming waves, these are termed edge waves. These edge waves become trapped near the shoreline and when two of them together from opposite directions, a standing edge wave is formed. The movement patterns of waves are fixed and so can be defined as two regions of interest, the nodal and antinodal points. The antinodal point is all the movement takes place as the water rises and falls, creating a series of peaks. Between these antinodal points are the points where no vertical movement takes place. An incoming wave has an almost uniform height but when it collides with a standing edge wave, if it collides with a peak, then the wave height is increased and if it collides with a trough, then its height is decreased. In the diagram on the right, the two cancel each other out, creating a flat surface. However, this is a simplified version of events. These are known as waves and are very uncommon
9.
Tide
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Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. Some shorelines experience a semi-diurnal tide—two nearly equal high and low tides each day, other locations experience a diurnal tide—only one high and low tide each day. A mixed tide—two uneven tides a day, or one high, Tides vary on timescales ranging from hours to years due to a number of factors. To make accurate records, tide gauges at fixed stations measure water level over time, gauges ignore variations caused by waves with periods shorter than minutes. These data are compared to the level usually called mean sea level. Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field varies in time. For example, the part of the Earth is affected by tides. Tide changes proceed via the following stages, Sea level rises over several hours, covering the intertidal zone, the water rises to its highest level, reaching high tide. Sea level falls over several hours, revealing the intertidal zone, the water stops falling, reaching low tide. Oscillating currents produced by tides are known as tidal streams, the moment that the tidal current ceases is called slack water or slack tide. The tide then reverses direction and is said to be turning, slack water usually occurs near high water and low water. But there are locations where the moments of slack tide differ significantly from those of high, Tides are commonly semi-diurnal, or diurnal. The two high waters on a day are typically not the same height, these are the higher high water. Similarly, the two low waters each day are the low water and the lower low water. The daily inequality is not consistent and is small when the Moon is over the equator. From the highest level to the lowest, Highest Astronomical Tide – The highest tide which can be predicted to occur, note that meteorological conditions may add extra height to the HAT. Mean High Water Springs – The average of the two high tides on the days of spring tides, mean High Water Neaps – The average of the two high tides on the days of neap tides. Mean Sea Level – This is the sea level
10.
Erosion
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In earth science, erosion is the action of surface processes that remove soil, rock, or dissolved material from one location on the Earths crust, then transport it away to another location. Eroded sediment or solutes may be transported just a few millimetres, the rates at which such processes act control how fast a surface is eroded. Feedbacks are also possible between rates of erosion and the amount of eroded material that is carried by, for example. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, while erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the rate of erosion in the region. Excessive erosion causes both on-site and off-site problems, on-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of bodies, as well as sediment-related damage to roads. Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion, however, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, and the surface runoff which may result from rainfall, produces four types of soil erosion, splash erosion, sheet erosion, rill erosion. Splash erosion is generally seen as the first and least severe stage in the erosion process. In splash erosion, the impact of a falling raindrop creates a crater in the soil. The distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rate is greater than the rate at which water can infiltrate into the soil. If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope, sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes, generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimetres or less and this means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow
11.
Sand
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Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt, Sand can also refer to a textural class of soil or soil type, i. e. a soil containing more than 85% sand-sized particles by mass. The second most common type of sand is calcium carbonate, for example aragonite, for example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non renewable resource over human timescales, and sand suitable for making concrete is in high demand, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this size is termed a sand grain. Sand grains are between gravel and silt, a 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers. ISO14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size, very fine sand, fine sand, medium sand, coarse sand, and very coarse sand. These sizes are based on the Krumbein phi scale, where size in Φ = -log2D, on this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers. The composition of sand is highly variable, depending on the local rock sources. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum, Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic with a high olivine content, many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, the study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the trade where it is preferred for concrete. Sand that is transported long distances by water or wind will be rounded, people who collect sand as a hobby are known as arenophiles
12.
Gravel
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Gravel /ˈɡrævəl/ is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel and pebble gravel, one cubic metre of gravel typically weighs about 1,800 kg. Gravel is an important commercial product, with a number of applications, many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac, both sand and small gravel are also important for the manufacture of concrete. Large gravel deposits are a geological feature, being formed as a result of the weathering. The action of rivers and waves tends to pile up gravel in large accumulations and this can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, quarries where gravel is extracted are known as gravel pits. Southern England possesses particularly large concentrations of them due to the deposition of gravel in the region during the Ice Ages. As of 2006, the United States is the leading producer and consumer of gravel. The word gravel comes from the Breton language, adding the -el suffix in Breton denotes the component parts of something larger. Thus gravel means the stones which make up such a beach on the coast. Many dictionaries ignore the Breton language, citing Old French gravele or gravelle, Gravel often has the meaning a mixture of different size pieces of stone mixed with sand and possibly some clay. American English also allows small stones without sand mixed in also known as crushed stone, types of gravel include, Bank gravel, naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. Also known as Bank run or River run, bench gravel, a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level. Creek rock, this is rounded, semi-polished stones, potentially of a wide range of types. It is also used as concrete aggregate and less often as a paving surface. Crushed stone, rock crushed and graded by screens and then mixed to a blend of stones and fines and it is widely used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, limestone, dolomite, also known as crusher run, DGA QP, and shoulder stone
13.
Self-organization
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Self-organization, also called spontaneous order, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process is spontaneous, not needing control by any external agent and it is often triggered by random fluctuations, amplified by positive feedback. The resulting organization is decentralized, distributed over all the components of the system. As such, the organization is typically robust and able to survive or self-repair substantial perturbation, chaos theory discusses self-organization in terms of islands of predictability in a sea of chaotic unpredictability. Self-organization occurs in physical, chemical, biological, robotic. Examples can be found in crystallization, thermal convection of fluids, chemical oscillation, animal swarming, self-organization is realized in the physics of non-equilibrium processes, and in chemical reactions, where it is often described as self-assembly. The concept has proven useful in biology, from molecular to ecosystem level, cited examples of self-organizing behaviour also appear in the literature of many other disciplines, both in the natural sciences and in the social sciences such as economics or anthropology. Self-organization has also observed in mathematical systems such as cellular automata. Self-organization is not to be confused with the concept of emergence. It states that any deterministic dynamic system automatically evolves towards a state of equilibrium that can be described in terms of an attractor in a basin of surrounding states, once there, the further evolution of the system is constrained to remain in the attractor. This constraint implies a form of mutual dependency or coordination between its constituent components or subsystems, in Ashbys terms, each subsystem has adapted to the environment formed by all other subsystems. The cybernetician Heinz von Foerster formulated the principle of order from noise in 1960 and it notes that self-organization is facilitated by random perturbations that let the system explore a variety of states in its state space. This increases the chance that the system will arrive into the basin of a strong or deep attractor, the thermodynamicist Ilya Prigogine formulated a similar principle as order through fluctuations or order out of chaos. It is applied in the method of simulated annealing for problem solving, the idea that the dynamics of a system can lead to an increase in its organization has a long history. The philosopher René Descartes presents it hypothetically in the part of his 1637 Discourse on Method. He elaborated on the idea in his unpublished work The World, such a system of organs must be able to behave as if it has a mind of its own, that is, it is capable of governing itself. Sadi Carnot and Rudolf Clausius discovered the Second Law of Thermodynamics in the 19th century and it states that total entropy, sometimes understood as disorder, will always increase over time in an isolated system. This means that a system cannot spontaneously increase its order, without a relationship that decreases order elsewhere in the system
14.
Sea level
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Mean sea level is an average level of the surface of one or more of Earths oceans from which heights such as elevations may be measured. A common and relatively straightforward mean sea-level standard is the midpoint between a low and mean high tide at a particular location. Sea levels can be affected by factors and are known to have varied greatly over geological time scales. The careful measurement of variations in MSL can offer insights into ongoing climate change, the term above sea level generally refers to above mean sea level. Precise determination of a sea level is a difficult problem because of the many factors that affect sea level. Sea level varies quite a lot on several scales of time and this is because the sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point, for example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. One measures the values of MSL in respect to the land, hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates. In the UK, the Ordnance Datum is the sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the datum was MSL at the Victoria Dock, in Hong Kong, mPD is a surveying term meaning metres above Principal Datum and refers to height of 1. 230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and it is used for a part of continental Europe and main part of Africa as official sea level. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001, height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum. It is also used in aviation, where some heights are recorded and reported with respect to sea level, and in the atmospheric sciences. An alternative is to base height measurements on an ellipsoid of the entire Earth, in aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights, however, differences up to 100 metres exist between this ellipsoid height and mean tidal height. The alternative is to use a vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, the elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, for one such case, see Amsterdam Airport Schiphol
15.
Coastal hazards
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Coastal Hazards are physical phenomena that expose a coastal area to risk of property damage, loss of life and environmental degradation. Slow-onset hazards develop incrementally over time periods and examples include erosion. This has led to population densities and high levels of development in many coastal areas. Along with this increase follows major investments in infrastructure and the build environment, the characteristics of coastal environments, however, pose some great challenges to human habitation. Coastlines are highly dynamic natural systems that interact with terrestrial, marine and atmospheric processes, over the years, human society has often failed to recognize the hazards related to these dynamics and this has led to major disasters and societal disruption to various degrees. Even today, coastal development is taking place with little regard to the hazards present in these environments. Societal activities in areas can also pose a hazard to the natural balance of coastal systems, thereby disrupting e. g. sensitive ecosystems. Coastal hazard management has become an important aspect of coastal planning in order to improve the resilience of society to coastal hazards. Possible management options include hard engineering structures, soft protection measures, events as the Hurricane Katrina affecting the southern USA in 2005 and the cyclone Nargis affecting Myanmar in 2008 provides clear examples of the importance of timely coastal hazard management. Let us take any country in the world, like the United States, there are many different types of environments along the coasts of the United States with very diverse features that affect, influence, and mold the near-shore processes that are involved. Understanding these ecosystems and environments can further advance the mitigating techniques and policy-making efforts against natural and these environments are heavily occupied with permafrost and glaciers, which are the two major conditions affecting Alaskas Coastal Development. The morphology of the types and sizes of barrier islands depend on the wave energy, tidal range, basement controls. The islands create multiple unique environments of wetland systems including marshes, estuaries and this region of landform is prone to natural disasters yet highly and continuously developed, with man-made structures attaining to water flow and control. This process is a significant buffer for the coastlines, naturally protecting and minimizing the impact of storm surge. Natural VS Human disasters The population that lives along or near our coastlines are a vulnerable population. There are numerous issues facing our coastlines and there are two categories that these hazards can be placed under, Natural disasters and Human disasters. Natural disasters are disasters that are out of control and are usually caused by the weather. Disasters that include but are not limited to, storms, tsunamis, typhoons, flooding, tides, waterspouts, noreasters, Human disasters occur when humans are the main culprit behind why the disaster happened
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Storm surge
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Most casualties during tropical cyclones occur as the result of storm surges. The deadliest storm surge on record was the 1970 Bhola cyclone, the low-lying coast of the Bay of Bengal is particularly vulnerable to surges caused by tropical cyclones. The deadliest storm surge in the twenty-first century was caused by the Cyclone Nargis, the next deadliest in this century was caused by the Typhoon Haiyan, which killed more than 6,000 people in the central Philippines in 2013 and resulted in economic losses estimated at $14 billion. Louis, Diamondhead and Pass Christian in Mississippi, a high storm surge occurred in New York City from Hurricane Sandy in October 2012, with a high tide of 14 ft. The pressure effects of a tropical cyclone will cause the level in the open ocean to rise in regions of low atmospheric pressure. The rising water level will counteract the low pressure such that the total pressure at some plane beneath the water surface remains constant. This effect is estimated at a 10 mm increase in sea level for every millibar drop in atmospheric pressure, strong surface winds cause surface currents at a 45° angle to the wind direction, by an effect known as the Ekman Spiral. Wind stresses cause a phenomenon referred to as wind set-up, which is the tendency for water levels to increase at the downwind shore, intuitively, this is caused by the storm simply blowing the water towards one side of the basin in the direction of its winds. Because the Ekman Spiral effects spread vertically through the water, the effect is proportional to depth. The pressure effect and the wind set-up on an open coast will be driven into bays in the way as the astronomical tide. The Earths rotation causes the Coriolis effect, which bends currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. When this bend brings the currents into more contact with the shore it can amplify the surge. The effect of waves, while powered by the wind, is distinct from a storms wind-powered currents. Powerful wind whips up large, strong waves in the direction of its movement, although these surface waves are responsible for very little water transport in open water, they may be responsible for significant transport near the shore. When waves are breaking on a more or less parallel to the beach. The rainfall effect is experienced predominantly in estuaries, Hurricanes may dump as much as 12 in of rainfall in 24 hours over large areas, and higher rainfall densities in localized areas. As a result, watersheds can quickly surge water into the rivers that drain them and this can increase the water level near the head of tidal estuaries as storm-driven waters surging in from the ocean meet rainfall flowing from the estuary. This situation well exemplified by the southeast coast of Florida
17.
Seawall
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A seawall is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a sea wall is to protect areas of habitation, conservation and leisure activities from the action of tides, waves. As a seawall is a feature it will conflict with the dynamic nature of the coast. The coast is generally a high-energy, dynamic environment with spatial variations over a range of timescales. The coast is exposed to erosion by rivers and winds as well as the sea, because of these persistent natural forces, sea walls need to be maintained to maintain their effectiveness. Sea walls are hard engineering shore-based structures which protect the coast from erosion, but various environmental problems and issues may arise from the construction of a sea wall, including disrupting sediment movement and transport patterns. Combined with a construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment. Sea walls may be constructed from various materials, most commonly reinforced concrete, boulders, steel, other possible construction materials are, vinyl, wood, aluminium, fibreglass composite, and large biodegrable sandbags made of jute and coir. In the UK, sea wall also refers to a bank used to create a polder. A seawall works by reflecting incident wave energy back into the sea, sea walls have two specific weaknesses. First, wave reflection from the wall may result in scour, second, sea walls may accelerate erosion of adjacent, unprotected coastal areas because they affect the littoral drift process. Different designs of man-made tsunami barriers include building reefs and forests to above-ground, in 2005, India began planting Casuarina and coconut saplings on its coast as a natural barrier against future tsunamis like the 2004 Indian Ocean earthquake. Studies have found that a tsunami wall could reduce tsunami wave heights by up to 83%. The design and type of sea wall that is appropriate depends on aspects specific to the location, a Japanese study of this tsunami in Sri Lanka used satellite imagery modelling to establish the parameters of coastal resistance as a function of different types of trees. Natural barriers, such as reefs and mangrove forests, prevent the spread of tsunamis. A cost benefit approach is a way to determine whether a seawall is appropriate. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural coastal ecosystems, a seawall is a static feature which can conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The table below summarises some positive and negative effects of seawalls which can be used when comparing their effectiveness with other coastal management options, such as beach nourishment
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Coastal erosion
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Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, drainage or high winds. The study of erosion and sediment redistribution is called coastal morphodynamics and it may be caused by hydraulic action, abrasion, impact and corrosion. On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which result in landforms such as tunnels, bridges, columns. Over time the coast generally evens out, the softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also abrasion commonly happens in areas where there are strong winds, loose sand, the blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks, the definition of abrasion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. A place where erosion of a cliffed coast has occurred is at Wamberal in the Central Coast region of New South Wales where houses built on top of the cliffs began to collapse into the sea. This is due to waves causing erosion of the sedimentary material on which the buildings foundations sit. Dunwich, the capital of the English medieval wool trade, disappeared over the period of a few due to redistribution of sediment by waves. The California coast, which has soft cliffs of sedimentary rock and is heavily populated, devils Slide, Santa Barbara, the coast just north of Ensenada, and Malibu are regularly affected. The Holderness coastline on the east coast of England, just north of the Humber Estuary, is one of the fastest eroding coastline in Europe due to its soft clay cliffs and powerful waves. Groynes and other measures to keep it under control has only accelerated the process further down the coast, because longshore drift starves the beaches of sand. The White Cliffs of Dover have also been affected, fort Ricasoli, a historic 17th century fortress in Malta is being threatened by coastal erosion, as it was built on a fault in the headland which is prone to erosion. A small part of one of the walls has already collapsed since the land under it has eroded. Hydraulic action occurs when striking a cliff face compress air in cracks on the cliff face. This exerts pressure on the rock, and can progressively splinter. Over time, the cracks can grow, sometimes forming a cave, the splinters fall to the sea bed where they are subjected to further wave action
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Wave
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In physics, a wave is an oscillation accompanied by a transfer of energy that travels through a medium. Frequency refers to the addition of time, wave motion transfers energy from one point to another, which displace particles of the transmission medium–that is, with little or no associated mass transport. Waves consist, instead, of oscillations or vibrations, around almost fixed locations, there are two main types of waves. Mechanical waves propagate through a medium, and the substance of this medium is deformed, restoring forces then reverse the deformation. For example, sound waves propagate via air molecules colliding with their neighbors, when the molecules collide, they also bounce away from each other. This keeps the molecules from continuing to travel in the direction of the wave, the second main type, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles. These types vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, waves are described by a wave equation which sets out how the disturbance proceeds over time. The mathematical form of this varies depending on the type of wave. Further, the behavior of particles in quantum mechanics are described by waves, in addition, gravitational waves also travel through space, which are a result of a vibration or movement in gravitational fields. While mechanical waves can be transverse and longitudinal, all electromagnetic waves are transverse in free space. A single, all-encompassing definition for the wave is not straightforward. A vibration can be defined as a back-and-forth motion around a reference value, however, a vibration is not necessarily a wave. An attempt to define the necessary and sufficient characteristics that qualify a phenomenon as a results in a blurred line. The term wave is often understood as referring to a transport of spatial disturbances that are generally not accompanied by a motion of the medium occupying this space as a whole. In a wave, the energy of a vibration is moving away from the source in the form of a disturbance within the surrounding medium and it may appear that the description of waves is closely related to their physical origin for each specific instance of a wave process. For example, acoustics is distinguished from optics in that sound waves are related to a rather than an electromagnetic wave transfer caused by vibration. Concepts such as mass, momentum, inertia, or elasticity and this difference in origin introduces certain wave characteristics particular to the properties of the medium involved
20.
Beach nourishment
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Beach nourishment is typically part of a larger coastal defense scheme. Nourishment is typically a repetitive process, since it does not remove the forces that cause erosion. The first nourishment project in the United States was at Coney Island and it is now a common shore protection measure utilized by public and private entities. Nourishment is one of three commonly accepted methods for protecting shorelines, the structural alternative involves constructing a seawall, revetment, groyne or breakwater. Alternatively, with managed retreat the shoreline is left to erode, while relocating buildings, Nourishment gained popularity because it preserved beach resources and avoided the negative effects of hard structures. Instead, nourishment creates a structure by creating a larger sand reservoir. Beaches can erode both naturally and due to human impacts, erosion is a natural response to storm activity. During storms, sand from the visible beach submerges to form sand bars that protect the beach, submersion is only part of the cycle. During calm weather smaller waves return sand from bars to the beach surface in a process called accretion. Some beaches do not have enough available to coastal processes to respond naturally to storms. When not enough sand is available, the beach cannot recover following storms, many areas of high erosion are due to human activities. Reasons can include, seawalls locking up sand dunes, coastal structures like ports and harbors that prevent longshore transport, dams, continuous, long-term renourishment efforts, especially in cuspate-cape coastlines, can play a role in longshore transport inhibition and downdrift erosion. The proportion of sand in a beach that lies below the waterline critically impacts beach nourishment. Two beaches with the amount of visible sand may be much different below the surface. An eroded beach with substantial submerged sand surrounding it may recover without nourishment, nourishing a beach that has little submerged sand requires understanding of the reason that the submerged sand is missing. The same forces that stripped the submerged sand once are likely to do so again, the amount of submerged sand eroded is typically much greater than the amount of missing sand on shore. Replacing only the sand is insufficient unless the submerged sand is also replaced. Otherwise, the beach is unstable and the sand quickly erodes
21.
Seawalls
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A seawall is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a sea wall is to protect areas of habitation, conservation and leisure activities from the action of tides, waves. As a seawall is a feature it will conflict with the dynamic nature of the coast. The coast is generally a high-energy, dynamic environment with spatial variations over a range of timescales. The coast is exposed to erosion by rivers and winds as well as the sea, because of these persistent natural forces, sea walls need to be maintained to maintain their effectiveness. Sea walls are hard engineering shore-based structures which protect the coast from erosion, but various environmental problems and issues may arise from the construction of a sea wall, including disrupting sediment movement and transport patterns. Combined with a construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment. Sea walls may be constructed from various materials, most commonly reinforced concrete, boulders, steel, other possible construction materials are, vinyl, wood, aluminium, fibreglass composite, and large biodegrable sandbags made of jute and coir. In the UK, sea wall also refers to a bank used to create a polder. A seawall works by reflecting incident wave energy back into the sea, sea walls have two specific weaknesses. First, wave reflection from the wall may result in scour, second, sea walls may accelerate erosion of adjacent, unprotected coastal areas because they affect the littoral drift process. Different designs of man-made tsunami barriers include building reefs and forests to above-ground, in 2005, India began planting Casuarina and coconut saplings on its coast as a natural barrier against future tsunamis like the 2004 Indian Ocean earthquake. Studies have found that a tsunami wall could reduce tsunami wave heights by up to 83%. The design and type of sea wall that is appropriate depends on aspects specific to the location, a Japanese study of this tsunami in Sri Lanka used satellite imagery modelling to establish the parameters of coastal resistance as a function of different types of trees. Natural barriers, such as reefs and mangrove forests, prevent the spread of tsunamis. A cost benefit approach is a way to determine whether a seawall is appropriate. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural coastal ecosystems, a seawall is a static feature which can conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The table below summarises some positive and negative effects of seawalls which can be used when comparing their effectiveness with other coastal management options, such as beach nourishment
22.
Jetty
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A jetty is a structure that projects from the land out into water. Often, jetty refers to a walkway accessing the centre of an enclosed waterbody, the term is derived from the French word jetée, thrown, and signifies something thrown out. The nes jetties at Dunkirk were founded in the beach, by the aid of compressed air. Below low water of spring tides, and their solid masonry portion, on a foundation was raised 50 feet. Above low water of neap tides, hence a bar is produced that diminishes the available depth in the approach channel. By carrying out a solid jetty over the bar, however on each side of the outlet, the currents are concentrated in the channel across the bar. Where a river is narrow near its mouth, has a generally feeble discharge and a tidal range. The channel, also, beyond the outlet of the river Nervion into the Bay of Biscay has been regulated by jetties, and by extending the south-west jetty out for nearly 0
23.
Breakwater (structure)
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Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and longshore drift. Breakwaters reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion or provide safe harbourage, Breakwaters may also be small structures designed to protect a gently sloping beach and put one to three hundred thousand feet onshore in relatively shallow water. An anchorage is only safe if ships anchored there are protected from the force of high winds, natural harbours are formed by such barriers as headlands or reefs. Artificial harbours can be created with the help of breakwaters, mobile harbours, such as the D-Day Mulberry harbours, were floated into position and acted as breakwaters. Some natural harbours, such as those in Plymouth Sound, Portland Harbour, the dissipation of energy and relative calm water created in the lee of the breakwaters often encourage accretion of sediment. However, this can lead to excessive salient build up, resulting in tombolo formation and this trapping of sediment can cause adverse effects down-drift of the breakwaters, leading to beach sediment starvation and increased erosion. This may then lead to further engineering protection being needed down-drift of the breakwater development, Breakwaters are subject to damage, and overtopping in severe storms events. Breakwaters can be constructed with one end linked to the shore, length of gap is largely governed by the interacting wavelengths. Breakwaters may be fixed or floating, and impermeable or permeable to allow sediment transfer shoreward of the structures. They usually consist of pieces of rock weighing up to 16 tonnes each. Their design is influenced by the angle of approach and other environmental parameters. Breakwater construction can be parallel or perpendicular to the coast. Of these three, the angle at which the breakwater is built is most important in the formation of salients. The angle at which the breakwater is built determines the new direction of the waves, a breakwater structure is designed to absorb the energy of the waves that hit it, either by using mass, or by using a revetment slope. In coastal engineering, a revetment is a land backed structure whilst a breakwater is a sea backed structure, caisson breakwaters typically have vertical sides and are usually erected where it is desirable to berth one or more vessels on the inner face of the breakwater. They use the mass of the caisson and the fill within it to resist the forces applied by waves hitting them. They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters, rubble mound breakwaters use structural voids to dissipate the wave energy. Rock or concrete armour units on the outside of the structure absorb most of the energy, the slopes of the revetment are typically between 1,1 and 1,2, depending upon the materials used
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Sea level rise
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Sea level rise refers to an increase in the volume of water in the world’s oceans, resulting in an increase in global mean sea level. Sea level rise is attributed to global climate change by thermal expansion of the water in the oceans and by melting of Ice sheets. Melting of floating ice shelves or icebergs at sea raises sea levels only slightly, Sea level rise at specific locations may be more or less than the global average. Local factors might include tectonic effects, subsidence of the land, tides, currents, storms, Sea level rise is expected to continue for centuries. IPCC Summary for Policymakers, AR5,2014, indicated that the mean sea level rise will continue during the 21st century, very likely at a faster rate than observed from 1971 to 2010. A January 2017 NOAA report suggests a range of GMSL rise of 0.3 –2.5 m possible during the 21st century, Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems. On the timescale of centuries to millennia, the melting of ice sheets could result in even higher sea level rise, partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, could contribute 4 to 6 m or more to sea level rise. Various factors affect the volume or mass of the ocean, leading to changes in eustatic sea level. The two primary influences are temperature, and the mass of water locked up on land and sea as water in rivers, lakes, glaciers. Over much longer timescales, changes in the shape of oceanic basins. Since the Last Glacial Maximum about 20,000 years ago, sea level has risen by more than 125 m, with rates varying from tenths of a mm/yr to 10+mm/year, as a result of melting of major ice sheets. During the rest of the early Holocene, the rate of sea level rise varied from a low of about 6.0 -9.9 mm/yr to as high as 30 -60 mm/yr during brief periods of accelerated sea level rise. In sharp contrast, the period between 14,300 and 11,100 calendar years ago, which includes the Younger Dryas interval, was an interval of reduced sea level rise at about 6.0 -9.9 mm/yr. Meltwater pulse 1C was centered at 8,000 calendar years, such rapid rates of sea level rising during meltwater events clearly implicate major ice-loss events related to ice sheet collapse. The primary source may have been meltwater from the Antarctic ice sheet, other studies suggest a Northern Hemisphere source for the meltwater in the Laurentide ice sheet. For example, this research included studies of Roman wells in Caesarea and these methods in combination suggest a mean eustatic component of 0.07 mm/yr for the last 2000 years. Since 1880, as the Industrial Revolution took center stage, the ocean began to rise briskly, climbing a total of 210 mm through 2009 causing extensive erosion worldwide, Sea level rose by 6 cm during the 19th century and 19 cm in the 20th century. Evidence for this includes geological observations, the longest instrumental records, for example, geological observations indicate that during the last 2,000 years, sea level change was small, with an average rate of only 0. 0–0.2 mm per year
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Coast
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A coastline or a seashore is the area where land meets the sea or ocean, or a line that forms the boundary between the land and the ocean or a lake. A precise line that can be called a coastline cannot be determined due to the Coastline paradox, the term coastal zone is a region where interaction of the sea and land processes occurs. Both the terms coast and coastal are often used to describe a location or region, for example, New Zealands West Coast. Edinburgh for example is a city on the coast of Scotland, a pelagic coast refers to a coast which fronts the open ocean, as opposed to a more sheltered coast in a gulf or bay. A shore, on the hand, can refer to parts of the land which adjoin any large body of water, including oceans. Similarly, the related term refers to the land alongside or sloping down to a river or to a body of water smaller than a lake. Bank is also used in parts of the world to refer to an artificial ridge of earth intended to retain the water of a river or pond. According to the UN atlas, 44% of people live within 150 kilometres of the sea, tides often determine the range over which sediment is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, the tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves, however, tidal bores can erode as the waves surge up river estuaries from the ocean. Waves erode coastline as they break on shore releasing their energy, the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas the wave energy breaking against the cliffs is higher, sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an abrasion or cliffed coast, sediment deposited by rivers is the dominant influence on the amount of sediment located on a coastline. Today riverine deposition at the coast is often blocked by dams and other human regulatory devices, like the ocean which shapes them, coasts are a dynamic environment with constant change. The coast and its adjacent areas on and off shore are an important part of a local ecosystem, Salt marshes and beaches also support a diversity of plants, animals and insects crucial to the food chain. The high level of biodiversity creates a level of biological activity. More and more of the people live in coastal regions
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Coastal management
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Coastal management is defense against flooding and erosion, and techniques that stop erosion to claim lands. Coastal zones occupy less than 15% of the Earths land area, nearly 1.2 billion people live within 100 km of a shoreline and 100 m of sea level, with an average density nearly 3 times higher than the global average for population. With three-quarters of the population expected to reside in the coastal zone by 2025. Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities, in the European Union, almost half of the population lives within 50 kilometres of the sea and coastal resources produce much of the Unions economic wealth. The fishing, shipping and tourism industries all compete for space along Europes estimated 89,000 km of coastline, Protection against sea level rise in the 21st century will be especially important, as sea level rise accelerates. Changes in sea level damage beaches and coastal systems, Coastal sediments are disturbed and suspended by wave and tide energy. Coastal engineering of harbours began with the origin of maritime traffic, docks, breakwaters and other harbour works were built by hand, often in a grand scale. Ancient harbour works are still visible, most of the grander ancient harbor works disappeared following the fall of the Western Roman Empire. Most coastal efforts were directed to port structures, venice and its lagoon is an example of measures not related to ports. Protection of the shore in Italy, England and the Netherlands began in the 6th century or earlier, the ancients understood phenomena such as Mediterranean currents and wind patterns and the wind-wave cause-effect link. The Romans introduced many innovations in harbor design and they built walls underwater and constructed solid breakwaters. In some cases wave reflection was used to prevent silting and they used surface-height breakwaters to trip the waves before they reached the main breakwater. They were the first dredgers in the Netherlands to maintain the harbour at Velsen, silting problems there were solved when the previously sealed solid piers were replaced with new open-piled jetties. Attack from the sea caused many coastal towns and their harbours to be abandoned, other harbours were lost due to natural causes such as rapid silting, shoreline advance or retreat, etc. The Venetian Lagoon was one of the few populated areas with continuous prosperity. Little improvement took place beyond the Roman approach to harbour construction after the Renaissance, prior to the 1950s, the general practice was to use hard structures to protect against beach erosion or storm damages. These structures included seawalls and revetments or sand-trapping structures such as groynes, during the 1920s and 30s, private or local community interests protected many coastal areas using these techniques on an ad hoc basis. In certain resort areas, structures proliferated to such an extent that the protection impeded recreational uses, erosion continued, but the structures remained, resulting in a loss of beach area
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Coastal geography
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Coastal geography is the study of the dynamic interface between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It involves an understanding of coastal weathering processes, particularly wave action, sediment movement and weather, the waves of different strengths that constantly hit against the shoreline are the primary movers and shapers of the coastline. Despite the simplicity of process, the differences between waves and the rocks they hit result in hugely varying shapes. The effect that waves have depends on their strength, strong waves, also called destructive waves, occur on high-energy beaches and are typical of winter. They reduce the quantity of sediment present on the beach by carrying it out to bars under the sea, constructive, weak waves are typical of low-energy beaches and occur most during summer. They do the opposite to destructive waves and increase the size of the beach by piling sediment up onto the berm, one of the most important transport mechanisms results from wave refraction. Since waves rarely break onto a shore at right angles, the movement of water onto the beach occurs at an oblique angle. However, the return of water is at right angles to the beach and this movement is known as beach drift. The endless cycle of swash and backwash and resulting beach drift can be observed on all beaches, probably the most important effect is longshore drift, the process by which sediment is continuously moved along beaches by wave action. LSD occurs because waves hit the shore at an angle, pick up sediment on the shore, due to gravity, the water then falls back perpendicular to the beach, dropping its sediment as it loses energy. The sediment is then picked up by the wave and pushed slightly further down the beach. This is the reason why long strips of coast are covered in sediment, not just the areas around river mouths, LSD helps create many landforms including barrier islands, bay beaches and spits. Onshore winds blowing up the beach, pick up sand and move it up the beach to form sand dunes, rain hits the shore and erodes rocks, and carries weathered material to the shoreline to form beaches. Warm weather can encourage biological processes to more rapidly. In tropical areas some plants and animals protect stones from weathering, while other plants, temperatures that vary from below to above freezing point result in frost weathering, whereas weather more than a few degrees below freezing point creates sea ice. In tropical regions in particular, plants and animals not only affect the weathering of rocks but are a source of sediment themselves, the shells and skeletons of many organisms are of calcium carbonate and when this is broken down it forms sediment, limestone and clay. The main physical Weathering process on beaches is salt-crystal growth, wind carries salt spray onto rocks, where it is absorbed into small pores and cracks within the rocks. There the water evaporates and the salt crystallises, creating pressure, in some beaches calcium carbonate is able to bind together other sediments to form beachrock and in warmer areas dunerock
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Landform
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A landform is a natural feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography, landforms are categorized by characteristic physical attributes such as elevation, slope, orientation, stratification, rock exposure, and soil type. Oceans and continents exemplify the highest-order landforms, landform elements are parts of a high-order landforms that can be further identified and systematically given a cohesive definition such as hill-tops, shoulders, saddles, foreslopes and backslopes. Some generic landform elements including, pits, peaks, channels, ridges, passes, pools, Terrain is the third or vertical dimension of land surface. Topography is the study of terrain, although the word is used as a synonym for relief itself. When relief is described underwater, the term bathymetry is used, in cartography, many different techniques are used to describe relief, including contour lines and TIN. Elementary landforms are the smallest homogeneous divisions of the land surface and these are areas with relatively homogeneous morphometric properties, bounded by lines of discontinuity. A plateau or a hill can be observed at various scales ranging from few hundred meters to hundreds of kilometers, hence, the spatial distribution of landforms is often scale-dependent as is the case for soils and geological strata. A number of factors, ranging from plate tectonics to erosion and deposition, can generate, landforms do not include man-made features, such as canals, ports and many harbors, and geographic features, such as deserts, forests, and grasslands. Many of the terms are not restricted to refer to features of the planet Earth, examples are mountains, hills, polar caps, and valleys, which are found on all of the terrestrial planets. The scientific study of landforms is known as geomorphology, landforms may be extracted from a digital elevation model using some automated techniques where the data has been gathered by modern satellites and stereoscopic aerial surveillance cameras. Until recently, compiling the data found in data sets required time consuming. The most detailed DEMs available are measured directly using LIDAR techniques, geomorphology Land List of landforms Open-geomorphometry project Terrain Open-Geomorphometry Project
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Anchialine pool
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An anchialine pool or pond is a landlocked body of water with a subterranean connection to the ocean. Depending on the site, it is possible to access the deeper saline water directly in the anchialine pool or sometimes it may be accessible by cave diving. Water levels in anchialine pools often fluctuate with tidal changes due to the coastal location, the range in water levels fluctuations will be decreased and delayed compared to the range and time observed for the adjacent tide. The primary controls on the damping and lag are the distance from the coast, Anchialine pools are extremely common worldwide especially along neo-tropical coastlines where the geology and aquifer system are relatively young, and there is minimal soil development. Such conditions occur notably where the bedrock is limestone or recently formed volcanic lava, many anchialine pools are found on the coastlines of the island of Hawaii, and on the Yucatán Peninsula, where they are locally called cenotes as well as Christmas Island. Ecological studies of anchialine pools frequently identify regionally rare and sometimes endemic species living in them, in Hawaii, the pools are home to mostly the ʻōpaeʻula. The Sailors Hat crater created by an explosives test in 1965 is an anchialine pool, brackish water Cenote Anchialine Pool Information United States Geological Survey, National Park Service 2005 Anchialine Caves and Cave Fauna of the World
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Archipelago
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An archipelago, sometimes called an island group or island chain, is a chain, cluster or collection of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi-, in Italian, possibly following a tradition of antiquity, the Archipelago was the proper name for the Aegean Sea and, later, usage shifted to refer to the Aegean Islands. It is now used to refer to any group or, sometimes. Archipelagos may be isolated in large amounts of water or neighbouring a large land mass. For example, Scotland has more than 700 islands surrounding its mainland which form an archipelago, archipelagos are often volcanic, forming along island arcs generated by subduction zones or hotspots, but may also be the result of erosion, deposition, and land elevation. Depending on their origin, islands forming archipelagos can be referred to as oceanic islands, continental fragments. Oceanic islands are mainly of volcanic origin, continental fragments correspond to land masses that have separated from a continental mass due to tectonic displacement. Indonesia, Japan, Taiwan, the Philippines, New Zealand, Maldives, the Bahamas, Greece, Hawaii, the largest archipelagic state in the world by area and population is Indonesia. Island arc List of landforms List of archipelagos by number of islands List of archipelagos List of islands Chisholm, Hugh, ed. Archipelago
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Atoll
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An atoll, sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands/cays on the rim, the coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the crater or caldera while the higher rim remains above water or at shallow depths that permit the coral to grow. For the atoll to persist, continued erosion or subsidence must be at a slow enough to permit reef growth upwards and outwards to replace the lost height. The word atoll comes from the Dhivehi word atholhu, meaning an administrative subdivision, the distribution of atolls around the globe is instructive, most of the worlds atolls are in the Pacific Ocean and Indian Ocean. The Atlantic Ocean has no large groups of atolls, other than eight atolls east of Nicaragua that belong to the Colombian department of San Andres and Providencia in the Caribbean. Reef-building corals will thrive only in tropical and subtropical waters of oceans and seas. The northernmost atoll of the world is Kure Atoll at 28°24 N, the southernmost atolls of the world are Elizabeth Reef at 29°58 S, and nearby Middleton Reef at 29°29 S, in the Tasman Sea, both of which are part of the Coral Sea Islands Territory. The next southerly atoll is Ducie Island in the Pitcairn Islands Group, at this latitude coral reefs would not develop without the warming waters of the Gulf Stream. However, Bermuda is termed a pseudo-atoll because its general form, while there is no atoll directly on the equator, the closest atoll to the Equator is Aranuka of Kiribati, with its southern tip just 12 km north of the equator. In most cases, the area of an atoll is very small in comparison to the total area. Atoll islands are low lying, with their elevations less than 5 meters, measured by total area, Lifou is the largest raised coral atoll of the world, followed by Rennell Island. More sources however list as the largest atoll in the world in terms of land area Kiritimati, the remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km², the largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a voyage aboard the HMS Beagle from 1831 to 1836. In time, subsidence carries the old volcano below the ocean surface, at this point, the island has become an atoll. Atolls are the product of the growth of marine organisms. Volcanic islands located beyond the water temperature requirements of hermatypic organisms become seamounts as they subside and are eroded away at the surface
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Avulsion (river)
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In sedimentary geology and fluvial geomorphology, avulsion is the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are less steep than the slope that the river could travel if it took a new course. Avulsions are common in river deltas, where sediment deposits as the river enters the ocean and this process is also known as delta switching. Deposition from the results in the formation of an individual deltaic lobe that pushes out into the sea. An example of a deltaic lobe is the delta of the Mississippi River. As the deltaic lobe advances, the slope of the channel becomes lower because the river channel is longer but has the same change in elevation. As the slope of the channel decreases, it becomes unstable for two reasons. First, water under the force of gravity will tend to flow in the most direct course downslope, if the river could breach its natural levees, it would spill out onto a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope. This will make it easier for the river to breach its levees, when this avulsion occurs, the new channel carries sediment out to the ocean, building a new deltaic lobe. This process is related to the distributary network of river channels that can be observed within a river delta. When the channel does this, some of its flow can remain in the abandoned channel, when these channel switching events happen repeatedly over time, a mature delta will gain a distributary network. Subsidence of the delta and/or sea-level rise can further cause backwater and this deposition fills the channels and leaves a geologic record of channel avulsion in sedimentary basins. On average, an avulsion will occur every time the bed of a river channel aggrades enough that the channel is superelevated above the floodplain by one channel-depth. In this situation, enough hydraulic head is available that any breach of the levees will result in an avulsion. Rivers can also avulse due to the erosion of a new channel that creates a path through the landscape. This can happen during large floods in situations in which the slope of the new channel is significantly greater than that of the old channel. Where the new channels slope is about the same as the old channels slope, an example of an erosional avulsion is the 2006 avulsion of the Suncook River in New Hampshire, in which heavy rains caused flow levels to rise. An example of an avulsion is known as a meander cutoff
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Barrier island
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Barrier islands are coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen and they are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend uninterrupted for over a hundred kilometers, excepting the tidal inlets that separate the islands, the longest and widest being Padre Island of Texas. The length and width of barriers and overall morphology of barrier coasts are related to parameters including tidal range, wave energy, sediment supply, sea-level trends, the amount of vegetation on the barrier has a large impact on the height and evolution of the island. Chains of barrier islands can be found along approximately thirteen percent of the worlds coastlines and they display different settings, suggesting that they can form and be maintained in a variety of environmental settings. Numerous theories have been given to explain their formation, lower shoreface The shoreface is the part of the barrier where the ocean meets the shore of the island. The barrier island body itself separates the shoreface from the backshore, characteristics common to the lower shoreface are fine sands with mud and possibly silt. Further out into the ocean the sediment becomes finer, the effect from the waves at this point is weak because of the depth. Bioturbation is common and many fossils can be found here, middle shoreface The middle shore face is located in the upper shoreface. The middle shoreface is strongly influenced by wave action because of its depth, closer to shore the grain size will be medium size sands with shell pieces common. Since wave action is heavier, bioturbation is not likely, upper shoreface The upper shore face is constantly affected by wave action. This results in development of sedimentary structures because of the constant differing flow of waves. Foreshore The foreshore is the area on land between high and low tide, like the upper shoreface, it is constantly affected by wave action. Cross bedding and lamination are present and coarser sands are present because of the energy present by the crashing of the waves. The sand is very well sorted. Backshore The backshore is always above the highest water level point, the berm is also found here which marks the boundary between the foreshore and backshore. Wind is the important factor here, not water, during strong storms high waves and wind can deliver and erode sediment from the backshore. Dunes The dunes are typical of an island, located at the top of the backshore
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Bay
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A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, lake, or another bay. A large bay may be called a gulf, sea, sound, a cove is a type of smaller bay with a circular inlet and narrow entrance. A fjord is a particularly steep bay shaped by glacial activity, bays can be the estuary of a river, such as the Chesapeake Bay, an estuary of the Susquehanna River, which is the largest bay in North America. Bays may also be nested within each other, for example, some large bays, such as the Bay of Bengal and the Hudson Bay, have varied marine geology. The land surrounding a bay often reduces the strength of winds, bays were significant in the history of human settlement because they provided a safe place for fishing. Later they were important in the development of sea trade as the safe anchorage they provide encouraged their selection as ports, there are various ways from which bays can be created. The largest bays have developed as a result of plate tectonics, as the super-continent Pangaea broke up along curved and indented fault lines, the continents moved apart and the worlds largest bays formed. These include the Gulf of Guinea, Gulf of Mexico and the Bay of Bengal, another way bays form is via glacial and river erosion. A bay formed by a glacier is a fjord, rias are created by rivers and are characterised by more gradual slopes. Currents can make waves more constant, and soft rocks speed erosion, hard rock eroded less quickly, leaving headlands. The Gulf of California is an example of a bay created by plate tectonics as Baja California peninsula moves away from the Mexican mainland, Bay platform Great capes Headlands and bays
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Baymouth bar
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A baymouth bar is a depositional feature as a result of longshore drift. It is a spit that completely closes access to a bay and it is different from a barrier island separating a lagoon because it closes the bay off completely, not partially. These bars usually consist of accumulated gravel and sand carried by the current of longshore drift, thus, they most commonly occur across artificial bay and river entrances due to the loss of kinetic energy in the current after wave refraction
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Bodden
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Bodden are briny bodies of water often forming lagoons, along the southwestern shores of the Baltic Sea, primarily in Germanys state of Mecklenburg-Vorpommern. These lagoons can be found especially around the island of Rügen, Usedom, some of them are protected reserves, forming the Western Pomerania Lagoon Area National Park. They have a geological origin and are enclosed by peninsulae, spits and islands. During the Littorina Sea transgression, an island archipelago was formed by the carving of narrow glacial basins, Bodden were formed in a comparatively short period between spits and offshore sandbars. These shallow glacial scoops were then subjected to extensive sedimentation during the Holocene, the frequent movement of water can lead to a scouring effect, but can also with heavy pollution show a tendency toward eutrophication. Due to erosion of cliffs and sedimentary deposition, the shape of the bodden coasts remains unstable, sudden changes have been caused by stormfloods, which repeatedly closed connections to the sea or opened new ones in the past. While bodden-type bays can be found in Mecklenburg and Denmark, the most typical bodden are located off the Pomeranian mainland between the mouth of the Recknitz river and the island of Usedom, to the south, the Bay of Greifswald comprises Gristower Inwiek, Kooser See and Dänische Wieck. The bodden are important sanctuaries for many species of birds and are important resting places for migratory birds like cranes. This was the reason for the establishment of the Western Pomerania Lagoon Area National Park, traditionally bodden have been good fishing areas, rich in mesolithic community sites, in particular the Pomeranian bodden of Rügen, Greifswald and Peenestrom. From these waters anglers regularly land 10–15 kg pike, harvesting the Sea, Farming the Forest by Marek Zvelebil, Lucyna Domańska, Robin Dennell YouTube - Angling in the Bodden
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Cape (geography)
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In geography, a cape is a headland or a promontory of large size extending into a body of water, usually the sea. A cape usually represents a change in trend of the coastline. Their proximity to the makes them prone to natural forms of erosion. This results in capes having a relatively short geologic lifespan, capes can be formed by glaciers, volcanoes, and changes in sea level. Erosion plays a role in each of these methods of formation. Eritrea–Sudan Ras Kasar Ghana Cape Coast Liberia Cape Mesurado - The Cape on which Monrovia is located, separates the Golden Horn Bay from the Sea of Marmara
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Channel (geography)
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In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, river delta or strait. The word is cognate to canal, and sometimes shows in this form, most examples of this are fjords in the Pacific Northwest, a notable exception is the Casiquiare canal. All likely share borrowing from Spanish, Portuguese or French, channels can be either natural or human-made. A channel is typically outlined in terms of its bed and banks, Channel initiation refers to the site on a mountain slope where water begins to flow between identifiable banks. This site is referred to as the head and it marks an important boundary between hillslope processes and fluvial processes. The channel head is the most upslope part of a network and is defined by flowing water between defined identifiable banks. A channel head forms as overland flow and/or subsurface flow accumulate to a point where shear stress can overcome resistance of the ground surface. Channel heads are associated with colluvium, hollows and landslides. Overland flow is a factor in channel initiation where saturation overland flow deepens to increase shear stress. Overland flows converge in topographical depressions where channel initiation begins, soil composition, vegetation, precipitation, and topography dictate the amount and rate of overland flow. The composition of a soil determines how quickly saturation occurs and cohesive strength retards the entrainment of material from overland flows, vegetation slows infiltration rates during precipitation events and plant roots anchor soil on hillslopes. Subsurface flow destabilizes soil and resurfaces on hillslopes where channel heads are often formed and this often results in abrupt channel heads and landslides. Natural channels are formed by fluvial process and are found across the Earth and these are mostly formed by flowing water from the hydrological cycle, though can also be formed by other fluids such as flowing lava. Channels also describe the course through a reef, sand bar, bay. One example is the Columbia River, a located in the US states of Washington and Oregon. A stream channel is the confine of a stream consisting of a bed. Stream channels exist in a variety of geometries, Stream channel development is controlled by both water and sediment movement. There is a difference between low gradient streams and high gradient streams, a wide variety of stream channel types can be distinguished
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Cliff
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In geography and geology, a cliff is a vertical, or nearly vertical, rock exposure. Cliffs are formed as erosion landforms by the processes of weathering, Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to weathering, sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs, an escarpment is a type of cliff, formed by the movement of a geologic fault or a landslide. Most cliffs have some form of slope at their base. In arid areas or under high cliffs, they are generally exposed jumbles of fallen rock, in areas of higher moisture, a soil slope may obscure the talus. Many cliffs also feature tributary waterfalls or rock shelters, sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining. Coastal erosion may lead to the formation of sea cliffs along a receding coastline, the Ordnance Survey distinguishes between cliffs and outcrops. Cliff is a Romance loanword that has its origins in the Latin forms clivus / clevus. Given that a cliff need not be vertical, there can be ambiguity about whether a given slope is a cliff or not. For example, given a vertical rock wall above a very steep slope. Listings of cliffs are thus inherently uncertain, some of the largest cliffs on Earth are found underwater. For example, an 8,000 m drop over a 4,250 m span can be found at a ridge sitting inside the Kermadec Trench. One candidate for highest cliff in the world is Nanga Parbats Rupal Face, according to other sources, the highest cliff in the world, about 1,340 m high, is the east face of Great Trango in the Karakoram mountains of northern Pakistan. The location of the worlds highest sea cliffs depends also on the definition of cliff that is used, guinness World Records states it is Kalaupapa, Hawaii, at 1,010 m high. Another contender is the face of Mitre Peak, which drops 1,683 m to Milford Sound. These are subject to a less stringent definition, as the slope of these cliffs at Kaulapapa is about 1.7, corresponding to an angle of 60 degrees. A more vertical drop into the sea can be found at Maujit Qaqarssuasia which is situated in the Torssukátak fjord area at the tip of South Greenland
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Continental margin
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The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Together, the shelf, continental slope, and continental rise are called the continental margin. Continental margins constitute about 28% of the oceanic area, the transition from continental to oceanic crust commonly occurs within the outer part of the margin, called the continental rise. Oceanwards, beyond the edge of the rise, lies the abyssal plain, the underwater part of the continental crust is the continental shelf, which usually abruptly terminates at the continental slope, which in turn terminates at the foot of the slope. The underwater part constitutes about 20% of the continental crust, the continental shelf is an expansive, shallow area of land extending outward from a continent. At the edge of that is the slope, a steep incline where several habitats exist. Earthquakes and volcanic eruptions are common on the west coast of North America, but there are no active volcanoes on the east coast, geologists refer to the west coast as a active continental margin, and the east coast as a passive continental margin. These differences can be found on several continents, most passive continental margins have broad continental shelves, whereas active continental margins typically have narrow continental shelves. In addition, active continental margins are near plate boundaries, whereas passive continental margins tend to be away from an active plate boundary
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Continental shelf
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The continental shelf is an underwater landmass which extends from a continent, resulting in an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods, the shelf surrounding an island is known as an insular shelf. The continental margin, between the shelf and the abyssal plain, comprises a steep continental slope followed by the flatter continental rise. Sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope, extending as far as 500 km from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope. The continental rises gradient is intermediate between the slope and the shelf, on the order of 0. 5–1°, the largest shelf – the Siberian Shelf in the Arctic Ocean – stretches to 1,500 kilometers in width. The South China Sea lies over another extensive area of shelf, the Sunda Shelf, which joins Borneo, Sumatra. Other familiar bodies of water that overlie continental shelves are the North Sea, the average width of continental shelves is about 80 km. The depth of the shelf also varies, but is limited to water shallower than 150 m. The slope of the shelf is quite low, on the order of 0. 5°, vertical relief is also minimal. Though the continental shelf is treated as a province of the ocean, it is not part of the deep ocean basin proper. Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to the deep sea. The shelf usually ends at a point of increasing slope, the sea floor below the break is the continental slope. Below the slope is the rise, which finally merges into the deep ocean floor. The continental shelf and the slope are part of the continental margin, the shelf area is commonly subdivided into the inner continental shelf, mid continental shelf, and outer continental shelf, each with their specific geomorphology and marine biology. The character of the shelf changes dramatically at the shelf break, with a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 140 m, this is likely a hallmark of past ice ages, when sea level was lower than it is now. The continental slope is steeper than the shelf, the average angle is 3°. The slope is cut with submarine canyons. The physical mechanisms involved in forming these canyons were not well understood until the 1960s, the continental shelves are covered by terrigenous sediments, that is, those derived from erosion of the continents
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Coral reef
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Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups, the polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support, most reefs grow best in warm, shallow, clear, sunny and agitated waters. Often called rainforests of the sea, shallow coral reefs form some of the most diverse ecosystems on Earth, paradoxically, coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at depths in tropical waters. Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection, the annual global economic value of coral reefs is estimated between US$29. 8-375 billion. However, coral reefs are fragile ecosystems, partly because they are sensitive to water temperature. Most of the coral reefs we can see today were formed after the last glacial period when melting ice caused the sea level to rise and this means that most modern coral reefs are less than 10,000 years old. As communities established themselves on the shelves, the reefs grew upwards, Reefs that rose too slowly could become drowned reefs. They are covered by so much water there was insufficient light. Coral reefs are found in the sea away from continental shelves, around oceanic islands. The vast majority of islands are volcanic in origin. The few exceptions have tectonic origins where plate movements have lifted the deep ocean floor on the surface. In 1842 in his first monograph, The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs and he theorized uplift and subsidence of the Earths crust under the oceans formed the atolls. Darwin’s theory sets out a sequence of three stages in atoll formation and it starts with a fringing reef forming around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the reef becomes a barrier reef. Darwin predicted that underneath each lagoon would be a bed rock base, where the level of the underlying earth allows, the corals grow around the coast to form what he called fringing reefs, and can eventually grow out from the shore to become a barrier reef
