Difference between revisions of "Template:This weeks featured article"

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'''Gravel Beaches'''
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''' Salinity sensors '''
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[[Image: electrode_conductivity.JPG | 300px| thumb |right| Electrode Conductivity principle]]
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Since as far as Ancient Greece times, attempts have been made to try to measure the "saltiness" of seawater. However, methods' efficiency was very incipient and their sensitivity and repeatability was very limited. During the Modern History more precise methodologies were developed: weighing after evaporation (Boyle,1693; Birch, 1965), solvent extraction (Lavoisier, 1772) and precipitation (Bergman, 1784).
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In 1865, Forchhammer introduced the term salinity and dedicated himself to measure individual components of seasalt rather than the total salinity. He found that the ratio of major salts in samples of seawater from various locations was constant. This constant ratio is known as Forchhammer's Principle, or the Principle of Constant Proportions. Towards the end of the nineteenth century, William Dittmar, following the work of Forchhammer, tested several methods to analyse the salinity and the chemical composition of seawater.
  
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[[Image:Sediment supply from soft cliffs.jpg|thumb|right|275px|Sediment supply from soft cliffs <br> © A. J. Chadwick]]
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Salinity is a ratio and not a physical parameter that can be measured(under PSS-78, see box). Thus, “Salinity sensors” do not exist. What is commonly referred to as a salinity sensor is in fact a conductivity sensor.
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Gravel beaches are widespread around the world, including the USA, Canada, Japan, Argentina, New Zealand and the wave dominated coastlines of Northern Europe. In the UK, about one third of the coastline is protected by such beaches.
 
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In coastal defence schemes, considerable use is made of coarse-grained (gravel) sediment to replenish [[Coast erosion|eroding beaches]], often in conjunction with structures such as rock or wooden [[groynes]] or offshore breakwaters. This is because such beaches are known to be an efficient form of natural coastal defence. Two examples from the UK are those at Sidmouth, Devon and Elmer, West Sussex.
 
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The emphasis of the article is to present in a clear and concise manner the most relevant concepts, basic understanding and insights into the behaviour of gravel beaches, to provide a summary of the available engineering analysis techniques and modelling approaches and to provide guidance to further reading and a list of the most relevant references to work carried out since 1990...
 

Revision as of 14:57, 2 July 2013

Salinity sensors

Electrode Conductivity principle

Since as far as Ancient Greece times, attempts have been made to try to measure the "saltiness" of seawater. However, methods' efficiency was very incipient and their sensitivity and repeatability was very limited. During the Modern History more precise methodologies were developed: weighing after evaporation (Boyle,1693; Birch, 1965), solvent extraction (Lavoisier, 1772) and precipitation (Bergman, 1784). In 1865, Forchhammer introduced the term salinity and dedicated himself to measure individual components of seasalt rather than the total salinity. He found that the ratio of major salts in samples of seawater from various locations was constant. This constant ratio is known as Forchhammer's Principle, or the Principle of Constant Proportions. Towards the end of the nineteenth century, William Dittmar, following the work of Forchhammer, tested several methods to analyse the salinity and the chemical composition of seawater.

Salinity is a ratio and not a physical parameter that can be measured(under PSS-78, see box). Thus, “Salinity sensors” do not exist. What is commonly referred to as a salinity sensor is in fact a conductivity sensor.

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