One third of the fresh water supply for the greater Los Angeles area comes from local groundwater sources. Atlantic Coast, as well as Southern California. The increased use of groundwater has caused the salt-water interface to move inland and closer to the ground surface along much of the U.S. Intrusion occurs in coastal aquifers worldwide, and is a growing issue in areas including North Africa, the Middle East, the Mediterranean, China, Mexico, and most notably, the Atlantic and Gulf Coasts of the United States, and Southern California. Incidents of saltwater intrusion have been detected as early as 1845 on Long Island, New York. Similar occurrences have been noted in the Mississippi River Valley Alluvial Aquifer in Arkansas, where in response to pumping, there is also upward movement of saline water from deeper formations (Reed, 2002). The more saline groundwater is brought to the surface through pumping for irrigation and other uses.
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Salinity issues in some regions surrounding the Rio Grande in New Mexico and Texas have been attributed to upwelling of deep-circulating groundwater, which is more saline due to natural underlying geologic formations (Doremus, 2008). Most incidents of saltwater intrusion occur in coastal regions, as has been the focus of discussion thus far, but inland areas can also be affected. Intrusion has also occurred in areas because of water levels being lowered by the construction of drainage canals (Barlow, 2003). Recharge rates can also be lowered in areas with increased urbanization and thus impervious surfaces. Saltwater intrusion into freshwater aquifers is also influenced by factors such as tidal fluctuations, long-term climate and sea level changes, fractures in coastal rock formations and seasonal changes in evaporation and recharge rates. Upward movement from deeper saline zones due to upconing near coastal discharge/pumping wells.Lateral encroachment from the ocean due to excessive water withdrawals from coastal aquifers, or.Generally, saltwater intrusion into coastal aquifers is caused by two mechanisms: According to this relation, if the water table in an unconfined coastal aquifer is lowered by 1 m, the salt-water interface will rise 40 m. This analysis assumes hydrostatic conditions in a homogeneous, unconfined coastal aquifer.
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X Groundwater Level Y Sea Water Level Salt-water interface in an unconfined coastal aquifer according to the Ghyben-Herzberg relation. Also, for every unit of groundwater above sea level there are 40 units of fresh water below sea level. The Ghyben-Herzberg Relation assumes, under hydrostatic conditions, the weight of a unit column of freshwater extending from the water table to the salt-water interface is balanced by a unit column of salt water extending from sea level to that same point on the interface. Therefore, the amount of fresh water stored in the aquifers is decreased (Barlow, 2003). Groundwater pumping/development can decrease the amount of fresh water flowing towards the coastal discharge areas, allowing salt water to be drawn into the fresh water zones of coastal aquifers. This natural movement of fresh water towards the sea prevents salt water from entering freshwater coastal aquifers (Barlow, 2003).
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In general, groundwater flows from areas with higher groundwater levels (hydraulic head) to areas with lower groundwater levels. Under normal conditions fresh water flows from inland aquifers and recharge areas to coastal discharge areas to the sea.
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The boundary between salt water and fresh water is not distinct the zone of dispersion, transition zone, or salt-water interface is brackish with salt water and fresh water mixing. Where groundwater is being pumped from aquifers that are in hydraulic connection with the sea, induced gradients may cause the migration of salt water from the sea toward a well, making the freshwater well unusable.īecause fresh water is less dense than salt water it floats on top. Saltwater intrusion is the induced flow of seawater into freshwater aquifers primarily caused by groundwater development near the coast. Saltwater intrusion is a major concern commonly found in coastal aquifers around the world. As the world's population continues to grow at an alarming rate, fresh water supplies are constantly being depleted, bringing with it issues such as saltwater intrusion and increasing the importance of groundwater monitoring, management, and conservation. Most of these coastal regions rely on groundwater as their main source of fresh water for domestic, industrial and agricultural purposes. Groundwater Monitoring, Management and Conservation Keep Saltwater Intrusion Under ControlĪlmost two thirds of the world's population lives within 400 km of the ocean shoreline just over half live within 200 km, an area only taking up 10% of the earth's surface (Hinrichsen, 2007).