Saltwater intrusion
Overview
 
Saltwater intrusion is the movement of saline water
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

 into freshwater aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

s. Most often, it is caused by ground-water pumping from coastal wells, or from construction of navigation channels or oil field canals. The channels and canals provide conduits for salt water to be brought into fresh water marshes. Salt water intrusion can also occur as the result of a natural process like a storm surge from a hurricane.
Encyclopedia
Saltwater intrusion is the movement of saline water
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

 into freshwater aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

s. Most often, it is caused by ground-water pumping from coastal wells, or from construction of navigation channels or oil field canals. The channels and canals provide conduits for salt water to be brought into fresh water marshes. Salt water intrusion can also occur as the result of a natural process like a storm surge from a hurricane. Saltwater intrusion occurs in virtually all coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

al aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

s, where they are in hydraulic continuity with seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...

.

Effect on drinking water

When fresh water is withdrawn at a faster rate than it can be replenished, the water table is drawn down as a result. This draw-down also reduces the hydrostatic pressure. When this happens near an ocean coastal area, salt water from the ocean is pulled into the fresh water aquifer. The result is that the aquifer becomes contaminated with salt water. This is happening to many coastal communities.

Hydrology

Saltwater intrusion happens when saltwater is drawn-in (from the sea
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

) into freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 aquifers. This behavior is caused because sea water has a higher density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 (which is because it carries more solutes) than freshwater. This difference in density causes the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 under a column of saltwater to be greater than the pressure under a column of the same height of freshwater. If these two columns are connected at the bottom, then the pressure difference would cause a flow of saltwater column to the freshwater column until the pressure equalizes.

The flow of saltwater inland is limited to coastal areas. Further inland, the freshwater column is higher due to the increasing altitude of the land and is able equalize the pressure from the salt water, stopping the saltwater intrusion. The higher water levels inland have another effect: the freshwater flows seaward. This completes the picture: at the sea-land boundary, at the high part of the aquifer freshwater flows out and in the lower part, saltwater flows in. The saltwater intrusion forms a wedge.

Pumping
Pumping
Pumping can refer to:*The operation of a pump, for moving a liquid from one location to another**The use of a breast pump or milking machine for extraction of milk*Gastric lavage The process of cleaning the contents of the stomach...

 of fresh water from an aquifer reduces the water pressure and intensifies the effect, drawing salt water into new areas. When freshwater levels drop, saltwater intrusion can proceed inland, reaching the pumped well
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...

. Then saltwater, unfit for drinking or irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

, is produced by the pump. To prevent this, more and more countries adopt extensive monitoring schemes and numerical models to assess how much water can be pumped without causing such effects.

Ghyben-Herzberg relation

The first physical formulations of saltwater intrusion were made by W. Badon-Ghijben (1888, 1889) and A. Herzberg (1901), thus called the Ghyben-Herzberg relation. They derived analytical solutions to approximate the intrusion behavior, which are based on a number of assumptions that do not hold in all field cases.



The figure shows the Ghyben-Herzberg relation. In the equation,
the thickness of the freshwater zone above sea level is represented as and that below sea level is represented as . The two thicknesses and , are related by and where is the density of freshwater and is the density of saltwater. Freshwater has a density of about 1.000 grams per cubic centimeter (g/cm3) at 20 °C, whereas that of seawater is about 1.025 g/cm3. The equation can be simplified to
.


The Ghyben-Herzberg ratio states, for every foot of fresh water in an unconfined aquifer above sea level, there will be forty feet of fresh water in the aquifer below sea level.

In the 20th century the higher computing
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 power allowed the use of numerical methods (usually finite difference
Finite difference
A finite difference is a mathematical expression of the form f − f. If a finite difference is divided by b − a, one gets a difference quotient...

s or finite elements) that need fewer assumptions and can be applied more generally.

Modeling

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
    Solvation
    Solvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...

     of calcium in the mixing zone and changing hydraulic properties.

  • The process known as cation exchange
    Ion exchange
    Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...

    , 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 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 would be expected based on the sea level, pumping scheme etc.

  • For long-term models, the future climate change
    Climate change
    Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

     forms a large unknown. Model results often depend strongly on sea level and recharge rate. Both are expected to change in the future.

Mitigation

Saltwater intrusion is also an issue where a lock separates salt water from fresh water (for example the Hiram M. Chittenden Locks
Hiram M. Chittenden Locks
The Hiram M. Chittenden Locks are a complex of locks that sit at the west end of Salmon Bay, part of Seattle's Lake Washington Ship Canal. They are known locally as the Ballard Locks after the neighborhood to their north...

 in Washington). 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
Fish ladder
A fish ladder, also known as a fishway, fish pass or fish steps, is a structure on or around artificial barriers to facilitate diadromous fishes' natural migration. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps into the waters on...

 to make it more attractive to migrating fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

.

See also

  • Aquifer
    Aquifer
    An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

  • Environmental migrant
  • Groundwater
    Groundwater
    Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

  • Garald G. Parker
    Garald G. Parker
    Garald G. "Jerry" Parker, Sr. was a hydrologist and is known as the "Father of Florida groundwater hydrology." Parker also named the principal artesian aquifer the Floridan Aquifer.- Education :...

  • Inflatable rubber dam
    Inflatable rubber dam
    Inflatable rubber dams are cylindrical rubber fabrics placed across channels, streams and weir or dam crests to raise the upstream water level when inflated. The membrane is a multi-layer fabric made of synthetic fibre and rubberised on one or both sides. The fabric is quite flexible and yet...

  • Living Waters for the World
    Living Waters for the World
    Living Waters for the World is a mission resource of the Synod of Living Waters of the Presbyterian Church . Its goal is to train and equip mission teams to empower local leaders to provide clean water to communities in need across the globe...

  • Peak water
    Peak water
    The term Peak Water has been put forward as a concept to help understand growing constraints on the availability, quality, and use of freshwater resources...

  • Sea level rise
  • Water well
    Water well
    A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...



Areas where water intrusion is occurring
  • Water supply and sanitation in Benin
    Water supply and sanitation in Benin
    Water supply and sanitation in Benin has been subject to considerable progress since the 1990s, in particular in rural areas, where coverage is higher than in many other African countries, and almost all development partners follow a national demand-responsive strategy, which has been adopted in 1992...

  • Geography of Cyprus
    Geography of Cyprus
    The geography of Cyprus included both the physical and human geography of Cyprus, an island country situated in the Eastern Basin of the Mediterranean Sea. Cyprus is third largest island in the Mediterranean and the world's 81st largest...

  • Bou Regreg
    Bou Regreg
    The Bou Regreg is a river located in western Morocco which discharges to the Atlantic Ocean between the cities of Rabat and Salé. The estuary of this river is termed Wadi Sala....

     (Morocco)
  • Water resources management in Pakistan
    Water resources management in Pakistan
    Water resources management in Pakistan.-Water resources:According to the United Nations' "UN World Water Development Report", the total actual renewable water resources decreased from 2,961 m³ per capita in 2000 to 1,420 m³ per capita in 2005...

  • Water supply and sanitation in Tunisia
    Water supply and sanitation in Tunisia
    Tunisia has achieved the highest access rates to water supply and sanitation services among the MENA countries through sound infrastructure policy. 96% of urban dwellers and 52% of the rural population already have access to improved sanitation. By the end of 2006, the access to safe drinking water...

  • United States
    • ACF River Basin
      ACF River Basin
      The ACF River Basin is the watershed of the Apalachicola/Chattahoochee/Flint River Basin, in the United States, that begins in northern Georgia and flows into the Gulf of Mexico at Apalachicola Bay, near Apalachicola, Florida...

       (Florida/Georgia)
    • Environment of Florida
      Environment of Florida
      The state of Florida in the United States possesses a rich and diverse array of land and marine life and a mild subtropical climate. These assets have drawn millions of people to settle in the once rural state over the last hundred years; Florida's population increases by about 1,000 residents each...

    • Hiram M. Chittenden Locks
      Hiram M. Chittenden Locks
      The Hiram M. Chittenden Locks are a complex of locks that sit at the west end of Salmon Bay, part of Seattle's Lake Washington Ship Canal. They are known locally as the Ballard Locks after the neighborhood to their north...

       (Washington)
    • Hutchinson Island (Georgia)
    • Lake Lanier
      Lake Lanier
      Lake Lanier is a reservoir in the northern portion of the U.S. state of Georgia. It was created by the completion of Buford Dam on the Chattahoochee River in 1956, and is also fed by the waters of the Chestatee River. The lake encompasses of water, and of shoreline at normal level, a "full...

       (Georgia)
    • Lake Pontchartrain
      Lake Pontchartrain
      Lake Pontchartrain is a brackish estuary located in southeastern Louisiana. It is the second-largest inland saltwater body of water in the United States, after the Great Salt Lake in Utah, and the largest lake in Louisiana. As an estuary, Pontchartrain is not a true lake.It covers an area of with...

       (Louisiana)
    • Miami River (Florida)
      Miami River (Florida)
      The Miami River is a river in the United States state of Florida that drains out of the Everglades and runs through the Downtown and the city of Miami. The long river flows from the terminus of the Miami Canal at Miami International Airport to Biscayne Bay...

    • San Leandro, California
      San Leandro, California
      San Leandro is a city in Alameda County, California, United States. It is considered a suburb of Oakland and San Francisco. The population was 84,950 as of 2010 census. The climate of the city is mild throughout the year.-Geography and water resources:...

    • Sonoma Creek
      Sonoma Creek
      Sonoma Creek is a stream in northern California. It is one of two principal drainages of southern Sonoma County, California, with headwaters rising in the rugged hills of Sugarloaf Ridge State Park and discharging to San Pablo Bay, the northern arm of San Francisco Bay. The watershed drained by...

      (California)
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