Bank Filtration – Nebraska Teachers Learn About Groundwater Supply
Is water from a well near a river actually groundwater?
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
Photo credit: Andrew Stone
The photograph to the left shows water supply wells close to the Missouri River at Nebraska City, NE. The view from the bus was taken during an American Ground Water Trust field-trip training program for teachers. Water utility staff explain the engineering principle of bank filtration systems. Securing safe reliable water supply and having citizens educated about basic hydrology are both important objectives!
The wellheads of the riverbank wells are raised above flood level with their pumping equipment protected in the “sheds on stilts.” Flood waters typically have high turbidity and increased contaminants. Protecting wellheads is essential for the thousands of vertical wells or collector wells in alluvial sediments close to rivers. Some of the water pumped from riverbank wells may be groundwater that was naturally moving towards the river, but the bulk of water pumped from wells close to rivers is subsurface flow from the riverbed to the aquifer, induced when pumping lowers the water table.
Riverbank filtration, sometimes called riparian groundwater, has been an accepted supply solution worldwide for millennia. Many high capacity systems installed in Europe in the 19th century are still in operation. The US has hundreds of large and small municipal systems that use bank filtration; for example, Louisville, KY, Des Moines, IA, Bismark, ND and Littleton, MA. Many riverbank systems use large diameter “Ranney” wells and some have horizontal well connections underneath the river. The eleven Nebraska City wells are vertical wells in alluvial sediments with a diameter of 18 inches and a depth of 85 feet.
Wells close to surface water are considered to have a risk of contaminants not usually found in true groundwater. The EPA has rules about the treatment of “groundwater under the influence of surface water.” However, water from alluvial wells near rivers requires much less treatment than water pumped directly from rivers. As water moves from the river to the well, chemical and biological processes in the aquifer remove pathogens, nitrogen, synthetic organic chemicals and pesticides resulting in treatment cost savings.
More Information
- RBFsim – A recent paper on Riverbank Filtration (RBF)
- Assessing RBF – Detailed technical information with over 100 references
- Whittman/Layne – Explanation of collector wells
“Tides They Are A-Changin’”,…Groundwater,…Ghost Forests
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
“Changin” sea levels are impacting groundwater along coasts, estuaries and tidal rivers.
Ghost forests provide dramatic visible evidence of changes in subsurface water quality.
A “ghost forest” of dead trees refers to places where previously healthy trees have died because of increasing salinity in the root zone. The photograph (right) is from the Maryland coast where in places trees have died but remain standing. Rising sea levels can impact subsurface water quality by saline intrusion contamination. Some estimates show current global average sea level rise to be as much as 3mm/year, (about 1/8 of an inch). The dying of trees is a visible manifestation of future economic impacts on infrastructure that are likely to be much greater than the ecological loss of trees as ghost forests.
Basic physics and geology explain the intrusion process in coastal aquifers. The subsurface seaward movement of fresh groundwater can prevent saltwater from encroaching on coastal aquifers. The position of the saline/fresh interface in aquifers (zone of dispersion) involves a balance between gravity induced seaward groundwater flow and the sea level baseline. Coastal aquifers can occur in many geological environments provided there is enough interconnected permeability for hydraulic contact between land and offshore. The USGS diagram indicates that impacts of reduced groundwater flow and/or a rise in sea water level baseline will move the boundary zone between saltwater and non-saline water landward, causing saline contamination of groundwater or completely replacing what was preciously fresh groundwater. Storm surges and coastal flooding related to sea level rise can also exacerbate low-lying coastal salinity changes.
Over recent decades, sea levels worldwide have increased relative to the land. Why? A principal reason is rising global temperatures causing thermal expansion of seawater. Changing weather patterns are also increasing the rates of ice melting from the poles and mountain glaciers. In addition, decades of depletion of groundwater from aquifers has added to ocean volume. In some places, land subsidence or geological instability has locally accelerated the landward impacts of saline intrusion.
Some of the challenges for water-related infrastructure will require coastal communities to invest billions of dollars to mitigate the effects of increasing salinity of groundwater and rises in the level of water tables.
- Increasing salinity will result in the abandonment of wells for drinking water supply and irrigation.
- Even if salinity increases are small, there is increased risk of corrosion of pumps and equipment.
- Onsite septic systems could fail if rising groundwater levels impact leach fields in coastal homes.
- Saline seepage into municipal sewer systems could require new treatment processes or relocation.
- Landfills and low lying contaminated areas risk leachate generation from rising groundwater.
- Riparian saltwater intrusion from all tidal waters and any hydraulically connected drainage ditches
- and canals can bring salinity issues many miles inland from the coast.
A huge engineering and planning response is needed for sea level changes affecting millions of citizens in low lying coastal cities. Policy procrastination may turn out to be very costly. Ghost forests are just one “canary in the coal mine” that has already fallen off its perch. It is not a time-distant risk. Has anybody noticed?
Next time you are relaxing on an ocean beach give some thought to what is happening at the saline freshwater interface below the beach, and ask yourself – where is the “zone of dispersion” and is it moving inland?.
More Information
- Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast, USGS https://pubs.usgs.gov/circ/2003/circ1262/
- Saltwater intrusion and sea level rise threatens U.S. rural coastal landscapes and communities. Link Scholarly article: 2024, O’Donnell et.al.
- Special Report on the Ocean and Cryosphere in a Changing Climate, IPCC https://www.ipcc.ch/srocc/ (Chapter 4)
“Jack and Jill went up the hill to fetch a pail of water,
Jack fell down and broke his crown and Jill came tumbling after”
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
What! – that first line is a great groundwater learning opportunity!
Have you ever realized that for many generations of young children the well-known Jack & Jill nursery rhyme, published in 1795, serves as their first introduction to groundwater! The rhyme provides four subliminal water resources messages:
1 Illustrations of the rhyme typically depicted a well with a rope and bucket. The message: there is water down the well, hidden in rocks and earth below ground level, (groundwater).
- To get the water out of the well there has to be some way to raise the water up to the surface.
In this case, a rope connected to a handle that works by muscle power. [Many 18th and 19th century illustrations show Jack & Jill as young children. However, even if they could reach the handle, lifting the bucket up the well is probably more than small children can manage!]
3.Once out of the well and into the bucket, the real work begins because the (heavy) water has to be carried (without spilling) from the well to the home. [For many, but not all, communities worldwide, pumps have transformed the chore of getting groundwater out of the well.]
4.Two-person teamwork may be needed when carrying a heavy bucket to ensure that the precious water arrives safely. [Pipelines have revolutionized “fetching water” although UNICEF reports that 2.1 billion people worldwide do not have access to safely managed water. Children often have “fetching” responsibility.]
The first line of the rhyme has relevance from a water perspective. There are also interesting backstories about the rhyme’s origins and meaning. The names Jack & Jill were typically used in the 16th century as generic names for a man and a woman or boy and girl. Shakespeare uses the names in the plays, A Midsummer Night’s Dream and Love’s Labor’s Lost.
The village Kilmersdon in western England claims to be the place where the rhyme originated. The village has a road sign claiming “ownership.” A local historian, Martin Horler, researched the folklore and gives a date of 1645, when according to legend, Jack and Jill (who are teenagers) climb a local hill called Badstone, and in a quarry at the top, a boulder falls and crushes Jack (broke his crown) and two days later the disaster is compounded when Jill dies in childbirth (came tumbling after). This disaster, (if true and the date accurate!) took place 150 years before the first known publication of the nursery rhyme, giving plenty of time for the words retelling the tragedy to be transformed. The water well origins of the story received supporting evidence in 1999 when an old well was discovered on the top of Badstone Hill in Kilmersdon. This gave the village “proof” that their claim to the origins of Jack & Jill was correct. Archaeologist Dr. Peter Addyman confirmed the 35 foot deep well’s 16th century origins and Kilmersdon doubled down on their claim to be the home of the Jack & Jill story.
A French claim to the rhyme’s origins is that the rhyme, (Jack et Jill la colline ont monté), originates from France’s Revolution. The words describe the demise of King Louis XVI who was guillotined in1793 (broke his crown) and his wife Marie Antoinette, who was beheaded the following year (came tumbling after).
Yet another suggestion of the rhyme’s meaning is that is satirizes England’s King Charles I, who in the 17th century tried to raise money by reducing (“tumbling down”) the volume of a Jack (1/8 pint), of beer or wine while keeping the same tax. The size reduction the gill (1/4 pint) would then come “tumbling after,” (Jack & Gill)
As is the case with many nursery rhymes, the origins of tragedy: “rocks crushing heads” “kings and queens beheaded” “raising taxes on drinks” may refer to real occurrences that are retold in a gentler form.
More Information
- The true meaning of dozens of nursery rhymes is documented and speculated in many publications, for example:
the book “Pop Goes the Weasel, The Secret Meaning of Nursery Rhymes” by Albert Jack, 2009, Penguin Books. - For information about Kilmersdon’s claim to be the “home of Jack & Jill”, go to Wikipedia or any search engine.
- Visit UNICEF for information about global drinking water challenges – https://www.unicef.org/wash/water-scarcity
Water from Owens Valley for Los Angeles Water Supply Includes Groundwater! Tribes Want it Back!
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
This Owens Lake picture has a groundwater backstory! | photo credit: Andrew Stone
Looks are deceiving! The placid reflections in this photograph of Owens Valley Lake disguise the realities of the negative economic, social and ecological results of “forced” water transfers from Mono Basin and Owens Valley. It is not generally recognized that groundwater is a significant component of the “stolen” water. Since the early 20th century, the Owens Valley and later, the Mono Lake hydrologic system have been systematically commandeered, and their streams, lakes and wetland ecosystems east of the Sierras have been continually deprived of adequate water.
The Owens River Valley is on the northeastern foothills of the Sierra Nevada mountains. Geologic faults and volcanic activity formed the Mono Lake basin over the last 5 million years. [LINK]
For the last 100+ years vast quantities of water have been diverted via pipelines, siphons, canals and aqueducts for water supply 200+ miles away in Los Angeles. Groundwater contributes to the flow of the diverted headwater streams and in addition, groundwater in the Owens Valley hydrologic system is also accessed by wells owned by the City of Los Angeles. In the 1940s, tunnels were constructed north from Owens Valley to the Mono Basin and 1970 a second aqueduct was built that doubled the capacity to divert water south to LA.
An October 18th , 2025, article by the Mojave Desert, journalist Ian James, published in the Los Angeles Times, reports that leaders of the Native tribes in the Owens Valley are asking the city to take less water because current groundwater pumping has dried up the few existing springs and negatively affected meadow vegetation. According to the L A Times article, the Owens Valley “once had so many springs, streams and wetlands that the Paiute and Shoshone people called their homeland Payahuunadü, (the land of flowing water.) Today, tribal members say LA’s extensive use of water has transformed the landscape, desiccating many springs and meadows, killing native grasses and altering the ecosystem.”
Since 1941 when flow to Mono Lake was diverted, the lake’s surface area has been reduced by over 60%, the lake level has dropped by 45 feet, and the lake salinity has doubled. In the 1970s and 1980s, groundwater pumping in Owens Valley also impacted groundwater dependent natural vegetation north of Owens Lake. Lowered lake levels have exposed dry lake beds at Mono Lake and Owens Valley Lake. Wind blowing the dust from the exposed lake beds causes toxic air quality challenges. Following a 1979 lawsuit by Inyo County and environmental organizations, the City of LA has been required to install dust suppression systems that spray water on the dry lakebed.
It seems ironic that some of the groundwater from wells, and rerouted flow from streams, that formerly maintained vibrant Owens Valley ecosystems, now has to be used for suppressing dust caused by diverting water to Los Angeles.
See the links below for much more information about this hydrological engineering controversy.
The information in this article shows just the tip of a very big (125 year old hydrological & political) iceberg!
Original aqueduct construction: https://waterandpower.org/museum/Construction_of_the_LA_Aqueduct.html
Mono Craters Tunnel: https://www.monolake.org/today/groundwater-exports-benefit-los-angeles-impact-mono-lake/
1970 Aqueduct: https://waterandpower.org/museum/A_Second_Aqueduct.html Toxic Dust: https://www.plantsciences.ucdavis.edu/news/eviner-nas-owens
2025 LA Times report: Ian James reports for the Los Angeles Times October 18, 2025, with photography by Carlin Stiehl
LA Dept of Water & Power – annual report: https://www.ladwp.com/sites/default/files/2024-06/2024%20Final%20Owens%20Valley%20Report.pdf
What Would Happen if Something Happened to Your Drinking Water Supply?
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
A “Sole Source Aquifer” (SSA) refers to a groundwater source (aquifer) that is a main source of drinking water for a designated area. The United States Environmental Protection Agency (EPA) defines a SSA as an aquifer supplying at least 50% of the drinking water consumed in the area overlying the aquifer. Sometimes the boundaries of the SSA include recharge areas that may lie beyond the actual aquifer. SSA designation is intended to protect drinking water supplies from overuse and contamination. There are regulations and land-use restrictions for SSA zones to reduce risks of the loss of water source inventory.
The declaration of a SSA is particularly important where losing an aquifer because of contamination could lead to negative economic consequences and huge engineering costs to bring in a replacement safe alternative water supply. The EPA has authority under the 1974 Safe Drinking Water Act to determine SSAs. There are 76 Federally designated SSAs in the USA. Some examples are: Eastern Snake River Plain (ID), New Jersey Coastal Plain,(NJ), Cape Cod, Nantucket & Martha’s Vineyard, (MA), Long Island, (NY), Edwards Aquifer,(TX), Biscayne Aquifer, (FL), Dayton Buried Valley, (OH), Tucson – Santa Cruz & Avra Basin, (AZ), Columbia and Yorktown Aquifer, (MD).
In addition, tens of thousands of communities have source water protection regulations for drinking water. “Watershed protection” road signs serve to remind citizens about the value of safe dependable drinking water. Here is brief background information about just four SSAs with links to more information.
Dayton, OH
A buried valley filled with glacial sediments is the sole source aquifer system that serves over 1.5 million people in the Dayton Ohio area. The sands and gravels deposited by meltwater from glaciers over 10,000 years ago are in some places 300 feet thick. Over much of the valley-fill aquifer the water table is close to the surface, making it vulnerable to the risk of surface contamination.
Edwards Aquifer, TX
The Edwards Aquifer is the source of water for about two million people in Texas, including the city of San Antonio. Artesian wells, and the springs where water emerges from the aquifer are vital for drinking water supply and ecology. The aquifer is made up of porous and permeable limestones that reach depths of 300 to 700 feet. The limestones are broken by faults and joints, making the aquifer recharge zone vulnerable to contamination. Because of regional tilting of the rocks millions of years ago, the limestones are exposed at the surface in some places (recharge zones) and in others are buried beneath layers of sediments (artesian zones).
Cape Cod Aquifer, MA
The aquifers of Cape Cod and the islands are comprised of sand and gravel deposits left behind by melting glaciers 15,000 to 20,000 years ago. The glacial sediments range in depth between 200 and 600 feet. The aquifers are recharged by rain and snowmelt, and because the sediments are permeable there are very few rivers or streams. Provided that there is not too much pumping, rainfall recharge maintains a “mound” of fresh groundwater that prevents seawater from migrating to inland wells. Managing SSAs in coastal areas involves closely monitoring water quality and restricting pumping in times of drought.
Cape Cod Aquifer, MA
This SSA covers over 10,000 square miles in Idaho between Wyoming and Oregon. The main aquifer comprises volcanic basalt rocks recharged by precipitation and surface steams. Because of past overuse by pumping, the whole aquifer is now carefully managed to increase recharge and reduce pumping. Sustainable irrigation for agriculture is of great economic importance, and the aquifer is also the sole source of drinking water for 300,000 people in eastern Idaho.
How About Walking Down to the Bottom of a Well With Your Bucket to Fetch Water?
Prepared by Andrew Stone, Hydrogeologist (andrewstonewater(at)gmail.com)
Did you know that there are over 3,000 stepwells in India with many others in arid countries? Water wells are typically constructed or drilled as simple vertical shafts. However, a stepwell is a large diameter excavation constructed to reach permanent groundwater. Access to the wellwater is via a series of stone steps down from the surface to the well water. At a time of low groundwater, it takes several staircases of steps down to reach the water level.
Locally known in India as baoli, the primary purpose of stepwells is to provide year-round availability for water, especially in arid and seasonally arid areas. To make groundwater available year-round stepwells are excavated to a depth just below the lowest expected groundwater level (water table). Steps in a series
of staircases allow people to walk down to reach the water. As the groundwater level rises in the well,
(in India, often as a result of seasonal monsoon rains) the lower steps become submerged and less staircases are used to reach the water.
The picture above shows the 100 ft deep Chand Baori stepwell. (The green color is the water!). The well was constructed in the 8th and 9th century and has a total of 3,500 steps in thirteen levels of stone staircases.
The picture on the left is of the 15th/16th century stepwell called Ujala. It has a less-complex design than Chand Baroi but operates on the same principle.
Stepwells had the primary secular purpose to supply water. However, over the centuries many took on additional significance that led to elaborate architecture and carvings to honor different religions and to give recognition to the dynasties and sultan rulers who financed the stepwell projects.
Still on the subject of history, during the 19th century when India was part of the British Empire, stepwells were decreed by colonial authorities to be unhealthy, and water supply was provided by drilled wells. Many stepwells were then closed and some were filled in, fell into disrepair or became dumps.
Fast forward to the 21st century, and with increasing population, increasing aridity and monsoonrain uncertainty, water managers in India have to consider all options. Many stepwells in India are now being cleaned out and recommissioned to augment supply sources. For example, groundwater is now restored as a supply source at stepwells in Jodhpur (Toorji ka jhalra stepwell) and in Rajasthan, (Moosi Rani Sagar stepwell).
Search the web for many sources of more information about these fascinating constructions that access groundwater. Wikipedia is a good starting point. Also, visit Stepwell Atlas for an interactive map of world stepwells. [Note – the two stepwells listed in the United States don’t function as traditional stepwells!]
Picture of the month prepared by Andrew Stone, Hydrogeologist, (andrewstone @ gmail.com)
HAND PUMP WITH NO HANDLE? A LEARNING OPPORTUNITY FOR THE WORLD
In 1854, in Soho, London – a pump handle was removed from a public water-supply well. Dr. John Snow has entered the history books because his detective work identified the contaminated public well as the source of a cholera outbreak. To prevent further infections, he had the authorities remove the pump handle to stop citizens from using the well.
In the mid 19th century, London, England, was a rapidly growing metropolis of over 2.5 million, with overcrowding, widespread poverty, and lack of sanitary services. With streams and ditches highly polluted, thousands of shallow wells were the only public water supply for many areas of London. Sewer systems were just developing, but cesspits served for most wastewater disposal. Outbeaks of cholera were common. At that time it was thought (incorrectly) that diseases were spread through the foul-smelling air in a process known as miasma.
In introductory classes, today’s students of public health, groundwater and water supply programs worldwide learn about the 1854 cholera outbreak in Soho, where 600 people in a small area died from cholera in just a few days. For groundwater specialists in particular, the case study of the outbreak is a classic lesson in contamination risk. The “detective work” by Dr. Snow who lived near Broad Street, (and who, incidentally, was a physician to Queen Victoria) identified the source of water contamination and the well pump handle was removed to prevent use of the unsafe supply. His work also provided clear evidence that ingesting cholera-contaminated water was the cause of the cholera outbreak, and he helped disprove the theory that miasma caused disease.
Dr Snow and local priest Henry Whitehead mapped homes where people had died. They identified that virtually all the cholera victims used the Broad Street pump for water. People in the same area who accessed different wells or who purchased water from water companies were not affected. Further investigation narrowed the origin of the August 30th outbreak to the death three days earlier, of a cholera infected five-month-old child, Francis Lewis at 40 Broad Street. The baby’s mother had washed the soiled diapers (also known at that time as tailclouts) from the cholera-infected baby and dumped the dirty water in a shallow cesspit. The crumbling cesspit brickwork was found to be just 2 feet 8 inches from the well, with the well water level just 8 feet below.
During the 19th century thousands of dug wells were needed for the rapid growth of London’s population. The geology below London comprises thin layers of sand & gravel, maybe up to 25 feet, overlying 150 to 200 feet of Eocene London Clay below which are aquifers with high quality groundwater in Cretaceous Chalk that underlies the whole London basin. Some of the “safe” water supply identified during the Broad Street cholera outbreak came from private water companies that sourced groundwater from chalk aquifers discharging as springs in Hertfordshire 40 miles north of London. The spring water was delivered to the city by canal and then by hollowed-out elm log pipe systems. That groundwater supply source in Hertfordshire continues to be part of London’s current water supply (but not via hollowed out logs!).
The Broad Street pump story provides us with basic lessons about wellhead protection and the critical importance of investment in urban sewers, water supply systems and properly constructed wells. [It is sad that today, 170+ years later, millions of people endure unsanitary conditions in slums and refugee camps in many parts of the world where the status of sanitation and water supply is reminiscent of London’s 1854 Broad Street.]
More information:
More information: Wikipedia Link
Other Research: Link to interesting research by Dave Boylan about Baby Francis Lewis
Picture of the month prepared by Andrew Stone, Hydrogeologist, (andrewstone @ gmail.com)
In the old days, geology surveys were carried out slowly and laboriously via the “soles of geologists’ boots.” Times and technology have changed. Adapting land-based methods, airborne geophysical exploration to map geology and hydrogeology has now gained rapid worldwide acceptance.
The photograph shows a helicopter carrying an airborne electromagnetic induction sensor over northeastern Wisconsin as part of a 2022 study to map aquifers. Data from the survey were used to create and refine models of water availability for Wisconsin’s resource managers and policy makers. The project was a collaboration by the U.S. Geological Survey and several Wisconsin state agencies.
By digitally mapping the subsurface from the air, airborne geophysical surveys by drone, helicopter or plane can rapidly provide high-resolution comprehensive subsurface information for geological, geotechnical and hydrogeological applications. Airborne survey data can be collected without ecological disturbance, disrupting agriculture or negotiating access to private land. Additional benefits result from access to inhospitable terrain and avoiding the logistics of adverse weather conditions for ground crews.
In 1855, back in the mid-19th century, Gaspar Tournachon patented the idea of aerial photographs for surveying. Early photography from hot air balloons showed the benefits of a “birds eye view” perspective of the earth. First adopted for mapping and military intelligence, use of an “eye in the sky “photography had many applications from the mid-19th to the mid-20th century.
Airborne geophysical surveys (mostly for oil and mineral exploration) began 70+ years ago after the Second World War and became “routine” in the late 60’s with increasing technological innovations for surveys of the electrical properties of the earth. In selecting the line of direction to fly surveys, operators need to account for direction of the Earth’s magnetic field in the target area and the orientation of known geological features related to the survey’s objectives. Airborne instruments are typically more sensitive than ground-based geophysics equipment because of the increased distance of the airborne signal from the land surface and subsurface under investigation.
Airborne geophysics digital data collection has huge time-saving cost benefits. By calibrating (ground truthing) airborne spatial data to existing borehole logs and geological maps, experts can identify groundwater aquifers, zones of water pollution or high groundwater salinity, determine how geology influences an aquifer’s three-dimensional geometry, select favorable areas for additional land-based assessment and select drilling sites to optimize the chances of successful wells.
Modern airborne geophysical surveys with various transmitters and receivers typically measure Earth’s magnetic field, naturally occurring gamma radiation and electrical conductivity. In addition, the tennis court-size platform arrays carried by helicopters, as shown in the USGS photograph, will probably also carry altimeters, video cameras and global positioning equipment.
Airborne geophysics surveys of the ground and subsurface are now one of the main tools in the geologists’ and hydrogeologists’ toolbox. With demographic pressures, changing weather patterns, and finite (although potentially renewable) water resources, accurate scientific resource assessments are crucial as the basis for water management decisions and the political prioritization of water allocation at local regional, national and global scale.
More information:
Wisconsin Survey (4 minute video): Southern Wisconsin Airborne Electromagnetic Survey 2022 | U.S. Geological Survey
Gaspar Tournachon: History of Aerial Photography
Airborne Geophysics:
https://colliergeophysics.com/airborne-geophysics/
https://csegrecorder.com/articles/view/the-application-of-airborne-geophysics-for-water-exploration
https://www.bing.com/videos/riverview/relatedvideo?q=+airborne+geophysics+for+groundwater+applications&mid=511DED9A46ACDCD923C5511DED9A46ACDCD923C5&FORM=VIRE
We have got another full line up of conferences for the month of April, check them out!
Clemson Hydrogeology Symposium – April 3-4 in Clemson, SC
Geology Techfest OSU – April 4-5 in Stillwater, OK
SAME San Antonio Post SBMRF – April 9-10 in San Antonio, TX
SAGEEP 3rd Munitions Response Meeting – April 13-17 in Denver, CO
AGWT-NCAAR Groundwater Conference – April 22-23 in Memphis, TN
ORWA Annual Conference – April 23-25 in Tulsa, OK
AIPG Texas GEODAYZ 2025 – April 25-26 in Stephenville, TX
Picture of the month prepared by Andrew Stone, Hydrogeologist, (andrewstone @ gmail.com)
The basic mechanism of ground surface subsidence is the compaction of sediments resulting from groundwater depletion in the aquifer(s) below. Aquifers with layers of fine-grained sediments are particularly vulnerable because they become compressible when dewatered by groundwater pumping. When water in the sediment pore spaces is removed, compaction may occur resulting in the clay layers occupying less space. Over time, and in places where there are thick aquifers with fine-grained layers, the compaction is transmitted upwards to the surface. Much of the damage from cracks and fissures on the surface to buildings, roads, canals, aqueducts, pipelines and well casing, results from uneven subsidence with differential vertical displacement causing sideways movements. Subsidence in coastal zones can greatly increase flooding risks. Pumping-related subsidence is not likely to occur in aquifers with mostly sandy sediments or in consolidated rock aquifers. It is the draining of water from saturated fine silt and clay layers that is the main subsidence culprit.
Groundwater-pumping-induced land subsidence is a worldwide phenomenon, not just in agricultural areas such as California’s Central Valley, but also in urban areas, for example, Mexico City, Mexico; Jakarta, Indonesia; Shanghai, China; Tehran, Iran; and Venice, Italy. The case of Venice serves to illustrate some of the cause and effect of pumping and the geological characteristics of aquifers where subsidence may occur.
Geologically, the 1,000-meter-thick layers of sediments beneath the Lagoon of Venice, where the City of Venice is situated, are Pleistocene-Holocene sequences of sands and silts deposited by rivers flowing southwards from the Alps. The original settlement of Venice was on small sandy islands in the lagoon surrounded by mud flats. Expansion of the city occurred by reclaiming and filling areas of the lagoon tidal flats.
During industrialization in the early 20th century, a manufacturing complex was built near Marghera on the edge of the Venice Lagoon. Groundwater pumping from the Quaternary aquifer to supply the industries resulted in subsidence extending beneath Venice City. Most pumping occurred between the 1930s and 1970s but subsidence continued even after pumping was curtailed. This anthropogenic-caused subsidence, added to rising sea levels and longer-term small increments of natural geologic subsidence has led to alarm and worldwide concern for the flood-compromised future of this famous heritage city.
Gravity-flow of water in the California Aqueduct is crucial to delivering water for irrigation in the Central Valley. However, according to the California Department of Water Resources, the volume of flow in the aqueduct, or hydraulic conveyance capacity, has been reduced by more than 40% because of subsidence from groundwater pumping and now requires a multi billion dollar solution.
According to the US Geological Survey, “…more than 80 percent of the identified subsidence in the USA has occurred because of exploitation of underground water, and the increasing development of land and water resources threatens to exacerbate existing land-subsidence problems and initiate new ones.”
More information: