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Encyclopedia > Saltwater intrusion

Saltwater intrusion is a natural process that occurs in virtually all coastal aquifers. It consists in salt water (from the sea) flowing inland in freshwater aquifers. This behaviour is caused by the fact that sea water has a higher density (which is because it carries more solutes) than freshwater. This higher density has the effect that the pressure beneath a column of saltwater is larger than that beneath a column of the same height of freshwater. If these columns were connected at the bottom, then the pressure difference would trigger a flow from the saltwater column to the freshwater column. This is precisely what happens in saltwater intrusion cases. A coastal image featured on a United States postal stamp. ... An aquifer is an underground layer of water-bearing permeable rock, or permeable mixtures of unconsolidated materials (gravel, sand, silt, or clay) (see also groundwater). ... A magnified crystal of salt In chemistry, salt is a term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ... The worlds oceans as seen from the South Pacific Ocean (from Okeanos, Greek for river, the ancient Greeks noticed that a strong current flowed off Gibraltar, and assumed it was a great river); covers almost three quarters (71%) of the surface of the Earth, and nearly half of the... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ...


The flow of saltwater inland is limited to coastal areas. Inland the freshwater column gets higher and the pressure at the bottom also gets higher. This compensates for the higher density of the saltwater column. Where this happens, saltwater intrusion stops. The word flow has several different meanings: In fluid mechanics, the word flow is often used to mean a complete description of the motion of a fluid. ...


The higher water levels inland have another effect: they trigger flow of freshwater seaward. This completes the picture: at the sea-land boundary, we have in the high part of the aquifer outflow of freshwater and in the lower part, inflow of saltwater. The saltwater intrusion gets a sort of cone shape.


Saltwater intrusion is natural process, but it becomes an environmental problem when excessive pumping of fresh water from an aquifer reduces the water pressure and intensifies the effect, drawing salt water into new areas. In telecommunication, pumping is the action of an oscillator that provides cyclic inputs to an oscillating reaction device. ...


When freshwater levels drop, the intrusion can proceed further inland until reaching the pumped well. Then you may get saltwater out of the pump, unfit for drinking or irrigation. To prevent this, more and more countries adopt extensive monitoring schemes and numerical models to assess how much can be pumped without causing such effects. For the Scottish football team, see Motherwell F.C. The Whole Earth Lectronic Link (or The WELL) is one of the oldest virtual communities still online. ... Drinking water This article focuses on water as we experience it every day. ... High-altitude aerial view of irrigation in the Heart of the Sahara Irrigation (in agriculture) is the replacement or supplementation of rainfall with water from another source in order to grow crops. ... An abstract model (or conceptual model) is a theoretical construct that represents physical, biological or social processes, with a set of variables and a set of logical and quantitative relationships between them. ...


The first physical formulations of saltwater intrusion were made by Badon and Ghyben-Herzberg. They derived analytical solutions to approximate the intrusion behaviour, which are based on a number of assumptions that do not hold in all field cases. In the 20th century the higher computing power allowed the use of numerical methods (usually `finite differences or finite elements) that need less assumptions and can be applied more generally. (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... A computer is a machine capable of undergoing complex calculations. ... In mathematics, a finite difference is like a differential quotient, except that it uses finite quantities instead of infinitesimal ones. ... Finite element analysis (FEA) or finite element method (FEM) is a numerical technique for solution of boundary-value problems. ...


Even so the modeling of saltwater intrusion is considered difficult. Some typical difficulties that arise are:

  • The possible presence of fissures and cracks and fractures in the aquifer, whose precise positions are unknown but which have great influence on the development of the saltwater intrusion
  • The possible presence of small scale heterogeneities in the hydraulic properties of the aquifer, which are too small to be take into account by the model but which may also have great influence on the development of the saltwater intrusion
  • The change of hydraulic properties by the saltwater intrusion. A mixture of saltwater and freshwater is often undersaturated with respect to calcium, triggering dissolution of calcium in the mixing zone and changing hydraulic properties.
  • The process known as cation exchange, which slows the advance of a saltwater intrusion and also slows the retreat of a saltwater intrusion.
  • The fact that saltwater intrusions are often not in equilibrium makes it harder to model. Aquifer dynamics tend to be pretty slow and it takes the intrusion cone a long time to adapt to changes in pumping schemes, rainfall, etc. So the situation in the field can be significantly different from what you would expect based on the sea level, pumping scheme etc.
  • For long-term models, the future climate change forms a big unknown. Model results often depend strongly on sea level and recharge rate. Both are expected to change the coming century.

Saltwater intrusion is also an issue where a lock separates salt water from fresh water (for example the Hiram M. Chittenden Locks). In this case a collection basin was built from which the salt water can be pumped back to the sea. Some of the intruding salt water is also pumped to the fish ladder to make it more attractive to migrating fish. Fissure is a groove, natural division, deep furrow, or cleft found in the brain, spinal cord, and liver; or an unnatural tract found most commonly in the anus. ... Dissolution can have the following meanings: In music dissolution is the separation of an inter-parametric unit into its component parts, where usually each part is developed independently. ... Ion exchange is a process in which ions are exchanged between a solution and an ion exchanger, an insoluble solid or gel. ... Look up equilibrium in Wiktionary, the free dictionary. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years Climate change refers to the variation in the Earths global climate or regional climates over time. ... Canal locks in England. ... The Hiram M. Chittenden Locks are a complex of locks that sit in the middle of Salmon Bay, part of Seattles Lake Washington Ship Canal. ... Pool-and-weir fish ladder at Bonneville Dam on the Columbia River Fishways, most commonly referred to as fish ladders but also known as fish passes, are structures placed on or around man-made barriers (such as dams and weirs) to assist the natural migration of diadromous fishes. ... Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) A fish is a poikilothermic (cold-blooded) water-dwelling...


 
 

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