Los Angeles
Content
Los Angeles
Insights Into GroundWater Resources
Los Angeles
Los Angeles county is situated in western United States in the State of California. Settled by early Spanish Settlers Los Angeles County was established on February 18, 1850 Current population of 10 million people.
Los Angeles Basin
Geology of Los Angeles Basin
The Los Angeles Basin is a structurally complex, polyphase Neogene basin in a tectonically active margin along the North American and Pacific plates in Southern California. The early basin development was in the mid-Miocene during an extensional phase associated with strike slip and rotation of the Transverse Ranges. Extension continued throughout the late Miocene and early Pliocene, followed by folding and thrusting from the early Pliocene to recent times. The mountains are still rising today and their erosion piled up formed the Los Angeles basin. This erosion process still continues today, with massive slides of mud, boulders and debris flowing into the nearby canyons.
Los Angeles Water Supply
Water is supplied to the City from the Los Angeles Aqueducts (LAA), local groundwater, and the Metropolitan Water District of Southern California (MWD). The LAA water is primarily fed by snowmelt runoff in the Eastern Sierra Nevada. Its former source of water was from Owens lake. 11% of the city¶s water supply are from local groundwater The MWD supplies the city with water from the Colorado River
Local Groundwater
The city holds right to four ground water basins. The basins are San Fernando, Sylmar, Central, and West Coast basin. San Fernando Basin Is the the Largest Of the four.
San Fernando valley groundwater Basin
It is the largest of the four basins. It consists of 112,000 acres and comprises 91.2 percent of total valley fill. The basin is bounded on the east and northeast by the San Rafael Hills, Verdugo Mountains, and San Gabriel Mountains. The basin is comprised of many layers of clay, sand and gravel. The aquifers in the Valley floor are known as alluvial aquifers These aquifers are water-bearing layers of sand and gravel deposited from the surrounding mountains over millions of years.
Aquifer Characteristics
There are three key water-bearing zones in the basin The recent or upper alluvium --- The upper alluvium extends from the ground surface to depths of roughly 200-250 feet. This zone is not fully saturated and the water levels there are quite sensitive to recharge and water usage The older or lower alluvium --- The lower alluvium extends to depths of 400-600 feet. This zone is separated from the upper zone by a layer of 50 feet of finer sediments. This layer serves as barrier protecting the lower zone from water quality problems in the upper zone The Saugas formation, or deep zone --- It extends to at least 1,200 feet below the ground surface. due to its depths it has been the leastexplored of the basin aquifers.
Most of the groundwater extraction from the basin has been from the upper and lower alluvial zones. This groundwater generally follows the path of the Los Angeles River, flowing from west to east across the valley. The groundwater levels of the basin has been at a decline since the late 1940¶s due to widespread urban and industrial use. A severe drought during the late 1940s and early 1950s was responsible for the initial decline in water levels.
Current ground water issues
In 1980, traces of industrial solvents, especially TCE and PCE, were detected in San Fernando Valley production wells. Soils underlying many prominent factories, situated at the eastern end of the basin was affected by spills and leaks of these compounds and other toxic chemicals. It is believed that the reduced pumping in the late 1970s was what brought the groundwater in contact with many of these spills. There were numerous leakages from the storage tanks of many gas stations. Another big issues in recent years has been the salt water intrusion in the Greater Los Angeles area.
Plume map showing the estimated extent of dissolved trichloroethylene (TCE) propagation in the San Fernando Valley's upper aquifer
Salt water intrusion in coastal aquifers
expansive growth of both population and high demands for water through the early 1900¶s caused potentiometric levels along the coastline to drop below sea level. As a result, a landwarddirected pressure gradient caused saltwater to begin invading coastal aquifers as early as the 1920¶s In the 1950¶s, sets of closely spaced wells were drilled to inject high-quality freshwater into the ground, creating hydraulic pressure ridges or ³barriers´ to saltwater intrusion
Mitigation methods
New studies by the U.S. Geological Survey and its cooperators show that the geology of the Los Angeles Basin is much more complex than originally conceived. A seismic profile from the Port of Long Beach shows the complex geology of the area. The sediment layers provide many potential pathways for saltwater intrusion. Extensive research is needed to better determine where and how fast water moves within the various beds of sediment both onshore and offshore.
Work cited
http://geopubs.wr.usgs.gov/factsheet/fs030-02/ http://www.ioe.ucla.edu/publications/r eport00/html/99revisited.html http://www.ladwp.com/water/supply/g rdwtr/ http://www.sosgear.com/la_map.htm http://quake.wr.usgs.gov/prepare/fact sheets/LADamStory/
Insights Into GroundWater Resources
Los Angeles
Los Angeles county is situated in western United States in the State of California. Settled by early Spanish Settlers Los Angeles County was established on February 18, 1850 Current population of 10 million people.
Los Angeles Basin
Geology of Los Angeles Basin
The Los Angeles Basin is a structurally complex, polyphase Neogene basin in a tectonically active margin along the North American and Pacific plates in Southern California. The early basin development was in the mid-Miocene during an extensional phase associated with strike slip and rotation of the Transverse Ranges. Extension continued throughout the late Miocene and early Pliocene, followed by folding and thrusting from the early Pliocene to recent times. The mountains are still rising today and their erosion piled up formed the Los Angeles basin. This erosion process still continues today, with massive slides of mud, boulders and debris flowing into the nearby canyons.
Los Angeles Water Supply
Water is supplied to the City from the Los Angeles Aqueducts (LAA), local groundwater, and the Metropolitan Water District of Southern California (MWD). The LAA water is primarily fed by snowmelt runoff in the Eastern Sierra Nevada. Its former source of water was from Owens lake. 11% of the city¶s water supply are from local groundwater The MWD supplies the city with water from the Colorado River
Local Groundwater
The city holds right to four ground water basins. The basins are San Fernando, Sylmar, Central, and West Coast basin. San Fernando Basin Is the the Largest Of the four.
San Fernando valley groundwater Basin
It is the largest of the four basins. It consists of 112,000 acres and comprises 91.2 percent of total valley fill. The basin is bounded on the east and northeast by the San Rafael Hills, Verdugo Mountains, and San Gabriel Mountains. The basin is comprised of many layers of clay, sand and gravel. The aquifers in the Valley floor are known as alluvial aquifers These aquifers are water-bearing layers of sand and gravel deposited from the surrounding mountains over millions of years.
Aquifer Characteristics
There are three key water-bearing zones in the basin The recent or upper alluvium --- The upper alluvium extends from the ground surface to depths of roughly 200-250 feet. This zone is not fully saturated and the water levels there are quite sensitive to recharge and water usage The older or lower alluvium --- The lower alluvium extends to depths of 400-600 feet. This zone is separated from the upper zone by a layer of 50 feet of finer sediments. This layer serves as barrier protecting the lower zone from water quality problems in the upper zone The Saugas formation, or deep zone --- It extends to at least 1,200 feet below the ground surface. due to its depths it has been the leastexplored of the basin aquifers.
Most of the groundwater extraction from the basin has been from the upper and lower alluvial zones. This groundwater generally follows the path of the Los Angeles River, flowing from west to east across the valley. The groundwater levels of the basin has been at a decline since the late 1940¶s due to widespread urban and industrial use. A severe drought during the late 1940s and early 1950s was responsible for the initial decline in water levels.
Current ground water issues
In 1980, traces of industrial solvents, especially TCE and PCE, were detected in San Fernando Valley production wells. Soils underlying many prominent factories, situated at the eastern end of the basin was affected by spills and leaks of these compounds and other toxic chemicals. It is believed that the reduced pumping in the late 1970s was what brought the groundwater in contact with many of these spills. There were numerous leakages from the storage tanks of many gas stations. Another big issues in recent years has been the salt water intrusion in the Greater Los Angeles area.
Plume map showing the estimated extent of dissolved trichloroethylene (TCE) propagation in the San Fernando Valley's upper aquifer
Salt water intrusion in coastal aquifers
expansive growth of both population and high demands for water through the early 1900¶s caused potentiometric levels along the coastline to drop below sea level. As a result, a landwarddirected pressure gradient caused saltwater to begin invading coastal aquifers as early as the 1920¶s In the 1950¶s, sets of closely spaced wells were drilled to inject high-quality freshwater into the ground, creating hydraulic pressure ridges or ³barriers´ to saltwater intrusion
Mitigation methods
New studies by the U.S. Geological Survey and its cooperators show that the geology of the Los Angeles Basin is much more complex than originally conceived. A seismic profile from the Port of Long Beach shows the complex geology of the area. The sediment layers provide many potential pathways for saltwater intrusion. Extensive research is needed to better determine where and how fast water moves within the various beds of sediment both onshore and offshore.
Work cited
http://geopubs.wr.usgs.gov/factsheet/fs030-02/ http://www.ioe.ucla.edu/publications/r eport00/html/99revisited.html http://www.ladwp.com/water/supply/g rdwtr/ http://www.sosgear.com/la_map.htm http://quake.wr.usgs.gov/prepare/fact sheets/LADamStory/
