![Pis pesio2](https://upload.wikimedia.org/wikipedia/commons/3/3a/Pis_pesio2.JPG)
Hydrogeology (''hydro-'' meaning water, and ''-geology'' meaning the study of the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
) is the area of
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
that deals with the distribution and movement of
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
in the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
and
rocks
In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...
of the Earth's
crust (commonly in
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
s). The terms groundwater hydrology, geohydrology, and hydrogeology are often used interchangeably.
Hydrogeology is the study of the laws governing the movement of subterranean water, the mechanical, chemical, and thermal interaction of this water with the porous solid, and the transport of energy, chemical constituents, and particulate matter by flow (Domenico and Schwartz, 1998).
Groundwater engineering, another name for hydrogeology, is a branch of
engineering
Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...
which is concerned with groundwater movement and design of wells, pumps, and drains. The main concerns in groundwater engineering include groundwater contamination, conservation of supplies, and water quality.
[Walton, William C. (November 1990). ''Principles of Groundwater Engineering,'' p. 1. CRC Press. .]
Wells are constructed for use in developing nations, as well as for use in developed nations in places which are not connected to a city water system. Wells must be designed and maintained to uphold the integrity of the aquifer, and to prevent contaminants from reaching the groundwater. Controversy arises in the use of groundwater when its usage impacts surface water systems, or when human activity threatens the integrity of the local aquifer system.
Introduction
Hydrogeology is an interdisciplinary subject; it can be difficult to account fully for the
chemical
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
,
physical
Physical may refer to:
*Physical examination
In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally co ...
,
biological and even
legal
Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vario ...
interactions between
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
,
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
,
nature
Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
and
society
A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same political authority and dominant cultural expectations. Socie ...
. The study of the interaction between groundwater movement and geology can be quite complex. Groundwater does not always follow the
surface topography
Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a surface from the per ...
; groundwater follows
pressure gradient
In atmospheric science, the pressure gradient (typically of Earth's atmosphere, air but more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure increases the most rapidly around a particu ...
s (flow from high pressure to low), often through fractures and conduits in circuitous paths. Taking into account the interplay of the different facets of a multi-component system often requires knowledge in several diverse fields at both the
experiment
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...
al and
theoretical
A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be ...
levels. The following is a more traditional introduction to the methods and nomenclature of saturated subsurface hydrology.
Hydrogeology in relation to other fields
![Лазоревый грот](https://upload.wikimedia.org/wikipedia/commons/c/c7/%D0%9B%D0%B0%D0%B7%D0%BE%D1%80%D0%B5%D0%B2%D1%8B%D0%B9_%D0%B3%D1%80%D0%BE%D1%82._%D0%9D%D0%B5%D0%B0%D0%BF%D0%BE%D0%BB%D1%8C.jpg)
Hydrogeology, as stated above, is a branch of the
earth science
Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres ...
s dealing with the flow of water through aquifers and other shallow
porous media
A porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas). The skeletal material is usu ...
(typically less than 450 m below the land surface). The very shallow flow of water in the subsurface (the upper 3 m) is pertinent to the fields of
soil science
Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to th ...
,
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
and
civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...
, as well as to hydrogeology. The general flow of
fluid
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
s (water,
hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
,
geothermal fluids, etc.) in deeper formations is also a concern of geologists,
geophysicists
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...
and
petroleum geologists
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
. Groundwater is a slow-moving,
viscous
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inter ...
fluid (with a
Reynolds number
In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be domi ...
less than unity); many of the empirically derived laws of groundwater flow can be alternately derived in
fluid mechanics
Fluid mechanics is the branch of physics concerned with the mechanics of fluids ( liquids, gases, and plasmas) and the forces on them.
It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and bio ...
from the special case of
Stokes flow (viscosity and
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
terms, but no inertial term).
![EVA- Lanxmeer piézomètre Piezometer 2009](https://upload.wikimedia.org/wikipedia/commons/e/e1/EVA-_Lanxmeer_pi%C3%A9zom%C3%A8tre_Piezometer_2009.jpg)
The
math
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
ematical relationships used to describe the flow of water through porous media are
Darcy's law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...
, the
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
and
Laplace equations, which have applications in many diverse fields. Steady groundwater flow (Laplace equation) has been simulated using
electrical
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
,
elastic
Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics.
Elastic may also refer to:
Alternative name
* Rubber band, ring-shaped band of rubber used to hold objects togeth ...
and
heat conduction
Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted .
Heat spontaneously flows along a te ...
analogies. Transient groundwater flow is analogous to the diffusion of
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
in a solid, therefore some solutions to hydrological problems have been adapted from
heat transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
literature.
Traditionally, the movement of groundwater has been studied separately from surface water,
climatology
Climatology (from Greek , ''klima'', "place, zone"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. This modern field of stud ...
, and even the chemical and
microbiological
Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, pro ...
aspects of hydrogeology (the processes are uncoupled). As the field of hydrogeology matures, the strong interactions between groundwater,
surface water
Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean.
The vast majority of surface water is produced by prec ...
,
water chemistry
Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water.
Chemic ...
, soil moisture and even
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
are becoming more clear.
California and Washington both require special certification of hydrogeologists to offer professional services to the public. Twenty-nine states require professional licensing for geologists to offer their services to the public, which often includes work within the domains of developing, managing, and/or remediating groundwater resources.
For example: aquifer
drawdown or
overdrafting
Overdrafting is the process of extracting groundwater beyond the equilibrium yield of an aquifer. Groundwater is one of the largest sources of fresh water and is found underground. Groundwater depletion is comparable to a bank account in which mor ...
and the pumping of
fossil water
Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vosto ...
may be a contributing factor to sea-level rise.
Subjects
![Water drop 001](https://upload.wikimedia.org/wikipedia/commons/5/5e/Water_drop_001.jpg)
One of the main tasks a hydrogeologist typically performs is the prediction of future behavior of an aquifer system, based on analysis of past and present observations. Some hypothetical, but characteristic questions asked would be:
*Can the aquifer support another
subdivision
Subdivision may refer to:
Arts and entertainment
* Subdivision (metre), in music
* ''Subdivision'' (film), 2009
* "Subdivision", an episode of ''Prison Break'' (season 2)
* ''Subdivisions'' (EP), by Sinch, 2005
* "Subdivisions" (song), by Rus ...
?
*Will the
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
dry up if the farmer doubles his
irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
?
*Did the chemicals from the
dry cleaning
Dry cleaning is any cleaning process for clothing and textiles using a solvent other than water.
Dry cleaning still involves liquid, but clothes are instead soaked in a water-free liquid solvent. Tetrachloroethylene (perchloroethylene), known in ...
facility travel through the aquifer to my well and make me sick?
*Will the plume of effluent leaving my neighbor's septic system flow to my drinking
water well
A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...
?
Most of these questions can be addressed through simulation of the hydrologic system (using numerical models or analytic equations). Accurate simulation of the aquifer system requires knowledge of the aquifer properties and boundary conditions. Therefore, a common task of the hydrogeologist is determining aquifer properties using
aquifer test An aquifer test (or a pumping test) is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" ( drawdown) in observation wells. Aquifer testing is a common tool that hydroge ...
s.
In order to further characterize aquifers and
aquitard
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
s some primary and derived physical properties are introduced below. Aquifers are broadly classified as being either confined or unconfined (
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
aquifers), and either saturated or unsaturated; the type of aquifer affects what properties control the flow of water in that medium (e.g., the release of water from storage for confined aquifers is related to the
storativity In the field of hydrogeology, ''storage properties'' are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy). According to '' ...
, while it is related to the specific yield for unconfined aquifers).
Aquifers
![Aquifer en](https://upload.wikimedia.org/wikipedia/commons/0/04/Aquifer_en.svg)
An
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
is a collection of water underneath the surface, large enough to be useful in a spring or a well. Aquifers can be unconfined, where the top of the aquifer is defined by the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
, or confined, where the aquifer exists underneath a confining bed.
[North Carolina Department of Environmental Quality (2018). ''Basic Hydrogeology.'' https://www.ncwater.org/?page=560]
There are three aspects that control the nature of aquifers:
stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks.
Stratigrap ...
,
lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
, and geological formations and deposits. The stratigraphy relates the age and geometry of the many formations that compose the aquifer. The lithology refers to the physical components of an aquifer, such as the mineral composition and grain size. The structural features are the elements that arise due to deformations after deposition, such as fractures and folds. Understanding these aspects is paramount to understanding of how an aquifer is formed and how professionals can utilize it for groundwater engineering.
[Birzeit University, Groundwater Engineering. ''Groundwater potential and Discharge Areas'' http://www.hwe.org.ps/Education/Birzeit/GroundwaterEngineering/Chapter%204%20-%20Groundwater%20Potential%20and%20Discharge%20Areas.pdf]
Hydraulic head
Differences in hydraulic head (''h'') cause water to move from one place to another; water flows from locations of high h to locations of low h. Hydraulic head is composed of pressure head (''ψ'') and elevation head (''z''). The head gradient is the change in hydraulic head per length of flowpath, and appears in
Darcy's law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...
as being proportional to the discharge.
Hydraulic head is a directly measurable property that can take on any value (because of the arbitrary datum involved in the ''z'' term); ''ψ'' can be measured with a pressure
transducer
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and contr ...
(this value can be negative, e.g., suction, but is positive in saturated aquifers), and ''z'' can be measured relative to a surveyed datum (typically the top of the
well
A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...
casing). Commonly, in wells tapping unconfined aquifers the water level in a well is used as a proxy for hydraulic head, assuming there is no vertical gradient of pressure. Often only ''changes'' in hydraulic head through time are needed, so the constant elevation head term can be left out (''Δh = Δψ'').
A record of hydraulic head through time at a well is a
hydrograph
A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).
It can als ...
or, the changes in hydraulic head recorded during the pumping of a well in a test are called
drawdown.
Porosity
![Well sorted vs poorly sorted porosity](https://upload.wikimedia.org/wikipedia/commons/b/b7/Well_sorted_vs_poorly_sorted_porosity.png)
Porosity (''n'') is a directly measurable aquifer property; it is a fraction between 0 and 1 indicating the amount of pore space between unconsolidated
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
particles or within a fractured rock. Typically, the majority of groundwater (and anything dissolved in it) moves through the porosity available to flow (sometimes called
effective porosity Effective porosity is most commonly considered to represent the porosity of a rock or sediment available to contribute to fluid flow through the rock or sediment, or often in terms of "flow to a borehole". Porosity that is not considered "effectiv ...
). Permeability is an expression of the connectedness of the pores. For instance, an unfractured rock unit may have a high ''porosity'' (it has many ''holes'' between its constituent grains), but a low ''permeability'' (none of the pores are connected). An example of this phenomenon is
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
, which, when in its unfractured state, can make a poor aquifer.
Porosity does not directly affect the distribution of hydraulic head in an aquifer, but it has a very strong effect on the migration of dissolved contaminants, since it affects groundwater flow velocities through an inversely proportional relationship.
Darcy's law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...
is commonly applied to study the movement of water, or other fluids through porous media, and constitutes the basis for many hydrogeological analyses.
Water content
Water content (''θ'') is also a directly measurable property; it is the fraction of the total rock which is filled with liquid water. This is also a fraction between 0 and 1, but it must also be less than or equal to the total porosity.
The water content is very important in
vadose zone
The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is f ...
hydrology, where the
hydraulic conductivity
Hydraulic conductivity, symbolically represented as (unit: m/s), is a property of porous materials, soils and rocks, that describes the ease with which a fluid (usually water) can move through the pore space, or fractures network. It depends on th ...
is a strongly
nonlinear
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
function of water content; this complicates the solution of the unsaturated groundwater flow equation.
Hydraulic conductivity
Hydraulic conductivity (''K'') and transmissivity (''T'') are indirect aquifer properties (they cannot be measured directly). ''T'' is the ''K'' integrated over the vertical thickness (''b'') of the aquifer (''T=Kb'' when ''K'' is constant over the entire thickness). These properties are measures of an
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
's ability to transmit
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
.
Intrinsic permeability (''κ'') is a secondary medium property which does not depend on the
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
and
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
of the fluid (''K'' and ''T'' are specific to water); it is used more in the petroleum industry.
Specific storage and specific yield
![Water table-season fluctuation](https://upload.wikimedia.org/wikipedia/commons/7/7c/Water_table-season_fluctuation.svg)
Specific storage (''S
s'') and its depth-integrated equivalent, storativity (''S=S
sb''), are indirect aquifer properties (they cannot be measured directly); they indicate the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1.
Specific yield (''S
y'') is also a ratio between 0 and 1 (''S
y'' ≤ porosity) and indicates the amount of water released due to drainage from lowering the water table in an unconfined aquifer. The value for specific yield is less than the value for porosity because some water will remain in the medium even after drainage due to intermolecular forces. Often the
porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
or effective porosity is used as an upper bound to the specific yield. Typically ''S
y'' is orders of magnitude larger than ''S
s''.
Fault zone hydrogeology
Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different
lithological settings, such as
clastic,
igneous
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
and
carbonate rock
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as dolosto ...
s. Fluid movements, that can be quantified as
permeability, can be facilitated or impeded due to the existence of a
fault zone
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
.
This is because different mechanism and deformed rocks can alter the porosity and hence the permeability within fault zone. Fluids involved generally are
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
(fresh and marine waters) and
hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
(Oil and Gas).
As fault zone is a zone of weakness that helps to increase the weathered zone thickness and hence the help in ground water recharge.
Along with
faults,
fractures
Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...
and
foliations also facilitate the groundwater mainly in hard rock terrains.
Contaminant transport properties
Often we are interested in how the moving groundwater will transport dissolved contaminants around (the sub-field of contaminant hydrogeology). The contaminants which are man-made (e.g.,
petroleum products
Petroleum products are materials derived from crude oil (petroleum) as it is processed in oil refineries. Unlike petrochemicals, which are a collection of well-defined usually pure organic compounds, petroleum products are complex mixtures. The m ...
,
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
,
Chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and hardne ...
or
radionuclides
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...
) or naturally occurring (e.g.,
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
,
salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
), can be transported through three main mechanisms, advection (transport along the main direction of flow at seepage velocity), diffusion (migration of the contaminant from high to low concentration areas), and dispersion (due to microscale heterogeneities present in the porous medium and non-uniform velocity distribution relative to seepage velocity). Besides needing to understand where the groundwater is flowing, based on the other hydrologic properties discussed above, there are additional aquifer properties which affect how dissolved contaminants move with groundwater.
Hydrodynamic dispersion
Hydrodynamic dispersivity (α
L, α
T) is an empirical factor which quantifies how much contaminants stray away from the path of the groundwater which is carrying it. Some of the contaminants will be "behind" or "ahead" the mean groundwater, giving rise to a longitudinal dispersivity (α
L), and some will be "to the sides of" the pure advective groundwater flow, leading to a transverse dispersivity (α
T). Dispersion in groundwater arises because each water "particle", passing beyond a soil particle, must choose where to go, whether left or right or up or down, so that the water "particles" (and their solute) are gradually spread in all directions around the mean path. This is the "microscopic" mechanism, on the scale of soil particles. More important, over long distances, can be the macroscopic inhomogeneities of the aquifer, which can have regions of larger or smaller permeability, so that some water can find a preferential path in one direction, some other in a different direction, so that the contaminant can be spread in a completely irregular way, like in a (three-dimensional) delta of a river.
Dispersivity is actually a factor which represents our ''lack of information'' about the system we are simulating. There are many small details about the aquifer which are effectively averaged when using a
macroscopic
The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic.
Overview
When applied to physical phenomena an ...
approach (e.g., tiny beds of gravel and clay in sand aquifers); these manifest themselves as an ''apparent'' dispersivity. Because of this, α is often claimed to be dependent on the length scale of the problem — the dispersivity found for transport through 1 m
3 of aquifer is different from that for transport through 1 cm
3 of the same aquifer material.
Molecular diffusion
Diffusion is a fundamental physical phenomenon, which
Albert Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
characterized as
Brownian motion
Brownian motion, or pedesis (from grc, πήδησις "leaping"), is the random motion of particles suspended in a medium (a liquid or a gas).
This pattern of motion typically consists of random fluctuations in a particle's position insi ...
, that describes the random thermal movement of molecules and small particles in gases and liquids. It is an important phenomenon for small distances (it is essential for the achievement of thermodynamic equilibria), but, as the time necessary to cover a distance by diffusion is proportional to the square of the distance itself, it is ineffective for spreading a solute over macroscopic distances. The diffusion coefficient, D, is typically quite small, and its effect can often be considered negligible (unless groundwater flow velocities are extremely low, as they are in clay aquitards).
It is important not to confuse diffusion with dispersion, as the former is a physical phenomenon and the latter is an empirical factor which is cast into a similar form as diffusion, because we already know how to solve that problem.
Retardation by adsorption
The retardation factor is another very important feature that make the motion of the contaminant to deviate from the average groundwater motion. It is analogous to the
retardation factor In chromatography, the retardation factor (''R'') is the fraction of an analyte in the mobile phase of a chromatographic system. In planar chromatography in particular, the retardation factor ''R''F is defined as the ratio of the distance traveled b ...
of
chromatography
In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
. Unlike diffusion and dispersion, which simply spread the contaminant, the retardation factor changes its ''global average velocity'', so that it can be much slower than that of water. This is due to a chemico-physical effect: the
adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
to the soil, which holds the contaminant back and does not allow it to progress until the quantity corresponding to the chemical adsorption equilibrium has been adsorbed. This effect is particularly important for less soluble contaminants, which thus can move even hundreds or thousands times slower than water. The effect of this phenomenon is that only more soluble species can cover long distances. The retardation factor depends on the chemical nature of both the contaminant and the aquifer.
History and development
Henry Darcy: 19th century
Henry Darcy
Henry Philibert Gaspard Darcy (, 10 June 1803 – 3 January 1858) was a French engineer who made several important contributions to hydraulics, including Darcy’s law for flow in porous media.
Early life
Darcy was born in Dijon, France, on J ...
was a French scientist who made advances in flow of fluids through porous materials. He conducted experiments which studied the movement of fluids through sand columns. These experiments led to the determination of
Darcy's law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...
, which describes fluid flow through a medium with high levels of porosity. Darcy's work is considered to be the beginning of quantitative hydrogeology.
Oscar Edward Meinzer: 20th century
Oscar Edward Meinzer
Oscar Edward Meinzer (November 28, 1876 – June 14, 1948) was an American hydrogeologist who has been called the "father of modern groundwater hydrology". He was awarded the William Bowie Medal
The William Bowie Medal is awarded annually by t ...
was an American scientist who is often called the "father of modern groundwater hydrology". He standardized key terms in the field as well as determined principles regarding occurrence, movement, and discharge. He proved that the flow of water obeys Darcy's law. He also proposed the use of geophysical methods and recorders on wells, as well as suggested pumping tests to gather quantitative information on the properties of aquifers. Meinzer also highlighted the importance of studying the geochemistry of water, as well as the impact of high salinity levels in aquifers.
Governing equations
Darcy's law
Darcy's law is a
constitutive equation
In physics and engineering, a constitutive equation or constitutive relation is a relation between two physical quantities (especially kinetic quantities as related to kinematic quantities) that is specific to a material or substance, and approx ...
, empirically derived by
Henry Darcy
Henry Philibert Gaspard Darcy (, 10 June 1803 – 3 January 1858) was a French engineer who made several important contributions to hydraulics, including Darcy’s law for flow in porous media.
Early life
Darcy was born in Dijon, France, on J ...
in 1856, which states that the amount of
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
discharging through a given portion of
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
is proportional to the cross-sectional area of flow, the
hydraulic gradient
Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22.
It is usually measured as a liquid surface elevation, expressed in units of length, ...
, and the
hydraulic conductivity
Hydraulic conductivity, symbolically represented as (unit: m/s), is a property of porous materials, soils and rocks, that describes the ease with which a fluid (usually water) can move through the pore space, or fractures network. It depends on th ...
.
Groundwater flow equation
![WellDrain2](https://upload.wikimedia.org/wikipedia/commons/0/05/WellDrain2.png)
The groundwater flow equation, in its most general form, describes the movement of groundwater in a porous medium (aquifers and aquitards). It is known in mathematics as the
diffusion equation
The diffusion equation is a parabolic partial differential equation. In physics, it describes the macroscopic behavior of many micro-particles in Brownian motion, resulting from the random movements and collisions of the particles (see Fick's la ...
, and has many analogs in other fields. Many solutions for groundwater flow problems were borrowed or adapted from existing
heat transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
solutions.
It is often derived from a physical basis using
Darcy's law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...
and a conservation of mass for a small control volume. The equation is often used to predict flow to
wells
Wells most commonly refers to:
* Wells, Somerset, a cathedral city in Somerset, England
* Well, an excavation or structure created in the ground
* Wells (name)
Wells may also refer to:
Places Canada
*Wells, British Columbia
England
* Wells ...
, which have radial symmetry, so the flow equation is commonly solved in
polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
* Polar climate, the c ...
or
cylindrical coordinates
A cylindrical coordinate system is a three-dimensional coordinate system that specifies point positions by the distance from a chosen reference axis ''(axis L in the image opposite)'', the direction from the axis relative to a chosen reference di ...
.
The
Theis equation Theis may refer to:
People
* Daniel Theis (born 1992), German basketball player
* Phil Theis, American professional wrestler
* Frank Gordon Theis, American federal judge
* Louis Fred Theis or Louis Fred Pfeifer, American Medal of Honor recipient ...
is one of the most commonly used and fundamental solutions to the groundwater flow equation; it can be used to predict the transient evolution of head due to the effects of pumping one or a number of pumping wells.
The
Thiem equation is a solution to the steady state groundwater flow equation (Laplace's Equation) for flow to a well. Unless there are large sources of water nearby (a river or lake), true steady-state is rarely achieved in reality.
Both above equations are used in
aquifer test An aquifer test (or a pumping test) is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" ( drawdown) in observation wells. Aquifer testing is a common tool that hydroge ...
s (pump tests).
The
Hooghoudt equation is a groundwater flow equation applied to
subsurface drainage
Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic condition ...
by pipes,
tile drains or ditches. An alternative subsurface drainage method is
drainage by wells Well drainage means drainage of agricultural lands by wells. Agricultural land is drained by pumped wells (vertical drainage) to improve the soils by controlling water table levels and soil salinity.
Introduction
Subsurface (groundwater) drainage f ...
for which groundwater flow equations are also available.
Calculation of groundwater flow
![Groundwater flow](https://upload.wikimedia.org/wikipedia/commons/c/c7/Groundwater_flow.svg)
To use the groundwater flow equation to estimate the distribution of hydraulic heads,
or the direction and rate of groundwater flow, this
partial differential equation
In mathematics, a partial differential equation (PDE) is an equation which imposes relations between the various partial derivatives of a Multivariable calculus, multivariable function.
The function is often thought of as an "unknown" to be sol ...
(PDE) must be solved. The most common means of analytically solving the diffusion equation in the hydrogeology literature are:
*
Laplace,
Hankel and
Fourier transforms (to reduce the number of
dimension
In physics and mathematics, the dimension of a Space (mathematics), mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any Point (geometry), point within it. Thus, a Line (geometry), lin ...
s of the PDE),
* similarity transform (also called the Boltzmann transform) is commonly how the
Theis solution is derived,
*
separation of variables
In mathematics, separation of variables (also known as the Fourier method) is any of several methods for solving ordinary and partial differential equations, in which algebra allows one to rewrite an equation so that each of two variables occurs ...
, which is more useful for non-Cartesian coordinates, and
*
Green's function
In mathematics, a Green's function is the impulse response of an inhomogeneous linear differential operator defined on a domain with specified initial conditions or boundary conditions.
This means that if \operatorname is the linear differential ...
s, which is another common method for deriving the Theis solution — from the
fundamental solution
In mathematics, a fundamental solution for a linear partial differential operator is a formulation in the language of distribution theory of the older idea of a Green's function (although unlike Green's functions, fundamental solutions do not ad ...
to the diffusion equation in free space.
No matter which method we use to solve the
groundwater flow equation Used in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar to ...
, we need both initial conditions
(heads at time (''t'') = 0) and
boundary conditions
In mathematics, in the field of differential equations, a boundary value problem is a differential equation together with a set of additional constraints, called the boundary conditions. A solution to a boundary value problem is a solution to th ...
(representing either the physical
boundaries of the domain, or an approximation of the domain beyond that
point). Often the initial conditions are supplied to a transient
simulation, by a corresponding steady-state simulation (where the time
derivative in the groundwater flow equation is set equal to 0).
There are two broad categories of how the (PDE) would be solved; either
analytical methods,
numerical methods, or something possibly in between. Typically, analytic methods solve the groundwater flow equation under a simplified set of conditions ''exactly'', while numerical methods solve it under more general conditions to an ''approximation''.
Analytic methods
Analytic methods typically use the structure of
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
to arrive at a simple, elegant solution, but the required derivation for all but the simplest domain geometries can be quite complex (involving non-standard
coordinate
In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sign ...
s,
conformal mapping
In mathematics, a conformal map is a function that locally preserves angles, but not necessarily lengths.
More formally, let U and V be open subsets of \mathbb^n. A function f:U\to V is called conformal (or angle-preserving) at a point u_0\in ...
, etc.). Analytic solutions typically are also simply an equation that can give a quick answer based on a few basic parameters. The
Theis equation Theis may refer to:
People
* Daniel Theis (born 1992), German basketball player
* Phil Theis, American professional wrestler
* Frank Gordon Theis, American federal judge
* Louis Fred Theis or Louis Fred Pfeifer, American Medal of Honor recipient ...
is a very simple (yet still very useful) analytic solution to the
groundwater flow equation Used in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar to ...
, typically used to analyze the results of an
aquifer test An aquifer test (or a pumping test) is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" ( drawdown) in observation wells. Aquifer testing is a common tool that hydroge ...
or
slug test
Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a s ...
.
Numerical methods
The topic of
numerical methods
Numerical analysis is the study of algorithms that use numerical approximation (as opposed to symbolic manipulations) for the problems of mathematical analysis (as distinguished from discrete mathematics). It is the study of numerical methods th ...
is quite large, obviously being of use to most fields of
engineering
Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...
and
science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
in general. Numerical methods have been around much longer than
computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
s have (In the 1920s
Richardson
Richardson may refer to:
People
* Richardson (surname), an English and Scottish surname
* Richardson Gang, a London crime gang in the 1960s
* Richardson Dilworth, Mayor of Philadelphia (1956-1962)
Places Australia
* Richardson, Australian Cap ...
developed some of the
finite difference
A finite difference is a mathematical expression of the form . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for t ...
schemes still in use today, but they were calculated by hand, using paper and pencil, by human "calculators"), but they have become very important through the availability of fast and cheap
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
s. A quick survey of the main numerical methods used in hydrogeology, and some of the most basic principles are shown below and further discussed in the
Groundwater model
Groundwater models are computer models of groundwater flow systems, and are used by hydrologists and hydrogeologists. Groundwater models are used to simulate and predict aquifer conditions.
Characteristics
An unambiguous definition of "groundwate ...
article.
There are two broad categories of numerical methods: gridded or discretized methods and non-gridded or mesh-free methods. In the common
finite difference
A finite difference is a mathematical expression of the form . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for t ...
method and
finite element method
The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat ...
(FEM) the domain is completely gridded ("cut" into a grid or mesh of small elements). The
analytic element method The analytic element method (AEM) is a numerical method used for the solution of partial differential equations. It was initially developed by O.D.L. Strack at the University of Minnesota. It is similar in nature to the boundary element method (BE ...
(AEM) and the boundary integral equation method (BIEM — sometimes also called BEM, or Boundary Element Method) are only discretized at boundaries or along flow elements (line sinks, area sources, etc.), the majority of the domain is mesh-free.
General properties of gridded methods
Gridded Methods like
finite difference
A finite difference is a mathematical expression of the form . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for t ...
and
finite element
The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat t ...
methods solve the groundwater flow equation by breaking the problem area (domain) into many small elements (squares, rectangles, triangles, blocks,
tetrahedra
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...
, etc.) and solving the flow equation for each element (all material properties are assumed constant or possibly linearly variable within an element), then linking together all the elements using
conservation of mass
In physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system's mass can ...
across the boundaries between the elements (similar to the
divergence theorem
In vector calculus, the divergence theorem, also known as Gauss's theorem or Ostrogradsky's theorem, reprinted in is a theorem which relates the ''flux'' of a vector field through a closed surface to the ''divergence'' of the field in the vol ...
). This results in a system which overall approximates the groundwater flow equation, but exactly matches the boundary conditions (the head or flux is specified in the elements which intersect the boundaries).
Finite differences
A finite difference is a mathematical expression of the form . If a finite difference is divided by , one gets a difference quotient. The approximation of derivatives by finite differences plays a central role in finite difference methods for the ...
are a way of representing continuous
differential operators using discrete intervals (''Δx'' and ''Δt''), and the finite difference methods are based on these (they are derived from a
Taylor series
In mathematics, the Taylor series or Taylor expansion of a function is an infinite sum of terms that are expressed in terms of the function's derivatives at a single point. For most common functions, the function and the sum of its Taylor serie ...
). For example, the first-order time derivative is often approximated using the following forward finite difference, where the subscripts indicate a discrete time location,
:
The forward finite difference approximation is unconditionally stable, but leads to an implicit set of equations (that must be solved using matrix methods, e.g.
LU or
Cholesky decomposition
In linear algebra, the Cholesky decomposition or Cholesky factorization (pronounced ) is a decomposition of a Hermitian, positive-definite matrix into the product of a lower triangular matrix and its conjugate transpose, which is useful for effici ...
). The similar backwards difference is only conditionally stable, but it is explicit and can be used to "march" forward in the time direction, solving one grid node at a time (or possibly in
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of ...
, since one node depends only on its immediate neighbors). Rather than the finite difference method, sometimes the Galerkin
FEM approximation is used in space (this is different from the type of FEM often used in
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
) with finite differences still used in time.
Application of finite difference models
MODFLOW
MODFLOW is the U.S. Geological Survey modular finite-difference flow model, which is a computer code that solves the groundwater flow equation. The program is used by hydrogeologists to simulate the flow of groundwater through aquifers. The sou ...
is a well-known example of a general finite difference groundwater flow model. It is developed by the
US Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, an ...
as a modular and extensible simulation tool for modeling groundwater flow. It is
free software
Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
developed, documented and distributed by the USGS. Many commercial products have grown up around it, providing
graphical user interface
The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
s to its input file based interface, and typically incorporating pre- and post-processing of user data. Many other models have been developed to work with MODFLOW input and output, making linked models which simulate several hydrologic processes possible (flow and transport models,
surface water
Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean.
The vast majority of surface water is produced by prec ...
and
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
models and chemical reaction models), because of the simple, well documented nature of MODFLOW.
Application of finite element models
Finite Element programs are more flexible in design (triangular elements vs. the block elements most finite difference models use) and there are some programs available (SUTRA, a 2D or 3D density-dependent flow model by the USGS;
Hydrus
Hydrus is a small constellation in the deep southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first appeared on a 35-cm (14 in) d ...
, a commercial unsaturated flow model;
FEFLOW
FEFLOW (Finite Element subsurface FLOW system) is a computer program for simulating groundwater flow, mass transfer and heat transfer in porous media and fractured media. The program uses finite element analysis to solve the groundwater flow equ ...
, a commercial modelling environment for subsurface flow, solute and heat transport processes; OpenGeoSys, a scientific open-source project for thermo-hydro-mechanical-chemical (THMC) processes in porous and fractured media;
COMSOL Multiphysics
COMSOL Multiphysics is a finite element analysis, solver, and simulation software package for various physics and engineering applications, especially coupled phenomena and multiphysics. The software facilitates conventional physics-based us ...
(a commercial general modelling environment),
FEATool Multiphysics
FEATool Multiphysics ("Finite Element Analysis Toolbox for Multiphysics") is a physics, finite element analysis (FEA), and PDE simulation toolbox. FEATool Multiphysics features the ability to model fully coupled heat transfer, fluid dynamics, ch ...
an easy to use MATLAB simulation toolbox, and Integrated Water Flow Model (IWFM), but they are still not as popular in with practicing hydrogeologists as MODFLOW is. Finite element models are more popular in
university
A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, t ...
and
laboratory
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physicia ...
environments, where specialized models solve non-standard forms of the flow equation (
unsaturated flow,
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
dependent flow, coupled
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
and groundwater flow, etc.)
Application of finite volume models
The finite volume method is a method for representing and evaluating partial differential equations as algebraic equations. Similar to the finite difference method, values are calculated at discrete places on a meshed geometry. "Finite volume" refers to the small volume surrounding each node point on a mesh. In the finite volume method, volume integrals in a partial differential equation that contain a divergence term are converted to surface integrals, using the divergence theorem. These terms are then evaluated as fluxes at the surfaces of each finite volume. Because the flux entering a given volume is identical to that leaving the adjacent volume, these methods are conservative. Another advantage of the finite volume method is that it is easily formulated to allow for unstructured meshes. The method is used in many computational fluid dynamics packages.
PORFLOW software package is a comprehensive mathematical model for simulation of Ground Water Flow and Nuclear Waste Management developed by Analytic & Computational Research, Inc., ACRi.
The
FEHM
FEHM is a groundwater model that has been developed in thEarth and Environmental Sciences Divisionat Los Alamos National Laboratory over the past 30 years. The executable is available free at thFEHM Website The capabilities of the code have expa ...
software package is available free from
Los Alamos National Laboratory
Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, ...
. This versatile porous flow simulator includes capabilities to model multiphase, thermal, stress, and multicomponent reactive chemistry. Current work using this code includes simulation of
methane hydrate
Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large am ...
formation,
CO2 sequestration,
oil shale extraction, migration of both nuclear and chemical contaminants, environmental isotope migration in the unsaturated zone, and
karst
Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...
formation.
Other methods
These include mesh-free methods like the
Analytic Element Method The analytic element method (AEM) is a numerical method used for the solution of partial differential equations. It was initially developed by O.D.L. Strack at the University of Minnesota. It is similar in nature to the boundary element method (BE ...
(AEM) and the Boundary Element Method (BEM), which are closer to analytic solutions, but they do approximate the groundwater flow equation in some way. The BEM and AEM exactly solve the groundwater flow equation (perfect mass balance), while approximating the boundary conditions. These methods are more exact and can be much more elegant solutions (like analytic methods are), but have not seen as widespread use outside academic and research groups yet.
Water wells
A
water well
A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...
is a mechanism for bringing groundwater to the surface by drilling or digging and bringing it up to the surface with a pump or by hand using buckets or similar devices. The first historical instance of water wells was in the 52nd century BC in modern-day
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
.
Today, wells are used all over the world, from developing nations to suburbs in the United States.
There are three main types of wells, shallow, deep, and artesian. Shallow wells tap into unconfined aquifers, and are, generally, shallow, less than 15 meters deep. Shallow wells have a small diameter, usually less than 15 centimeters. Deep wells access confined aquifers, and are always drilled by machine. All deep wells bring water to the surface using mechanical pumps. In artesian wells, water flows naturally without the use of a pump or some other mechanical device. This is due to the top of the well being located below the water table.
Water well design and construction
![Well In Kerala](https://upload.wikimedia.org/wikipedia/commons/c/ca/Well_In_Kerala.JPG)
One of the most important aspects of groundwater engineering and hydrogeology is water well design and construction. Proper well design and construction are important to maintain the health of the groundwater and the people which will use the well. Factors which must be considered in well design are:
* A reliable aquifer, providing a continuous water supply
* The quality of the accessible groundwater
* How to monitor the well
* Operating costs of the well
* Expected yield of the well
* Any prior drilling into the aquifer
There are five main areas to be considered when planning and constructing a new water well, along with the factors above. They are:
* Aquifer Suitability
* "Well Design Considerations
* Well Drilling Methods
* Well Screen Design and Development
* Well Testing"
[Matlock, Dan. 'Fundamentals of Water Well Design, Construction and Testing.' Pacific Groundwater Group.]
Aquifer suitability starts with determining possible locations for the well using "
USGS
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...
reports, well logs, and cross sections" of the aquifer. This information should be used to determine aquifer properties such as depth, thickness, transmissivity, and well yield. In this stage, the quality of the water in the aquifer should also be determined, and screening should occur to check for contaminants.
After factors such as depth and well yield are determined, the well design and drilling approach must be established. Drilling method is selected based on "soil conditions, well depth, design, and costs."
At this stage, cost estimates are prepared, and plans are adjusted to meet budgetary needs.
Important parts of a well include the well seals, casings or liners, drive shoes, well screen assemblies, and a sand or gravel pack (optional). Each of these components ensures that the well only draws from one aquifer, and no leakage occurs at any stage of the process.
There are several methods of drilling which can be used when constructing a water well. They include: "Cable tool, Air rotary, Mud rotary, and Flooded reverse circulation dual rotary" drilling techniques.
Cable tool drilling is inexpensive and can be used for all types of wells, but the alignment must be constantly checked and it has a slow advance rate. It is not an effective drilling technique for consolidated formations, but does provide a small drilling footprint. Air rotary drilling is cost effective and works well for consolidated formations. It has a fast advance rate, but is not adequate for large diameter wells. Mud rotary drilling is especially cost effective for deep wells. It maintains good alignment, but requires a larger footprint. It has a very fast advance rate. Flooded reverse circulation dual rotary drilling is more expensive, but good for large well designs. It is versatile and maintains alignment. It has a fast advance rate.
Well screens ensure that only water makes it to the surface, and sediments remain beneath the Earth's surface. Screens are placed along the shaft of the well to filter out sediment as water is pumped towards the surface. Screen design can be impacted by the nature of the soil, and natural pack designs can be used to maximize efficiency.
After construction of the well, testing must be done to assess productivity, efficiency and yield of the well, as well as determine the impacts of the well on the aquifer. Several different tests should be completed on the well in order to test all relevant qualities of the well.
Issues in groundwater engineering and hydrogeology
Contamination
Groundwater contamination happens when other fluids seep into the aquifer and mix with existing groundwater. Pesticides, fertilizers, and gasoline are common contaminants of aquifers. Underground storage tanks for chemicals such as gasoline are especially concerning sources of groundwater contamination. As these tanks corrode, they can leak, and their contents can contaminate nearby groundwater. For buildings which are not connected to a
wastewater treatment
Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...
system, septic tanks can be used to dispose of waste at a safe rate. If septic tanks are not built or maintained properly, they can leak bacteria, viruses and other chemicals into the surrounding groundwater. Landfills are another potential source of groundwater contamination. As trash is buried, harmful chemicals can migrate from the garbage and into the surrounding groundwater if the protective base layer is cracked or otherwise damaged. Other chemicals, such as road salts and chemicals used on lawns and farms, can runoff into local reservoirs, and eventually into aquifers. As water goes through the water cycle, contaminants in the atmosphere can contaminate the water. This water can also make its way into groundwater.
Controversy
Fracking
Contamination of groundwater due to fracking has long been debated. Since chemicals commonly used in
hydraulic fracturing
Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
are not tested by government agencies responsible for determining the effects of fracking on groundwater, laboratories at the
United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, or EPA, have a hard time determining if chemicals used in fracking are present in nearby aquifers. In 2016, the EPA released a report which states that drinking water can be contaminated by fracking. This was a reversal of their previous policies after a $29 million study into the effects of fracking on local drinking water.
California
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
sees some of the largest controversies in groundwater usage due to the dry conditions California faces, high population, and intensive agriculture. Conflicts generally occur over pumping groundwater and shipping it out of the area, unfair use of water by a commercial company, and contamination of groundwater by development projects. In
Siskiyou County
Siskiyou County (, ) is a county in the northernmost part of the U.S. state of California. As of the 2020 census, the population was 44,076. Its county seat is Yreka and its highest point is Mount Shasta. It falls within the Cascadia bioregion ...
in northern California, the
California Superior Court ruled poor groundwater regulations have allowed pumping to diminish the flows in the Scott River and disturbed the natural habitat of salmon. In
Owens Valley
Owens Valley (Numic
Numic is a branch of the Uto-Aztecan language family. It includes seven languages spoken by Native American peoples traditionally living in the Great Basin, Colorado River basin, Snake River basin, and southern Great Pl ...
in central California, groundwater was pumped for use in fish farms, which resulted in the death of local meadows and other ecosystems. This resulted in a lawsuit and settlement against the fish companies. Development in southern California is threatening local aquifers, contaminating groundwater through construction and normal human activity. For example, a solar project in
San Bernardino County
San Bernardino County (), officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California, and is located within the Inland Empire area. As of the 2020 U.S. Census, the population was 2,181, ...
would allegedly threaten the ecosystem of bird and wildlife species because of its use of up to 1.3 million cubic meters of groundwater, which could impact
Harper Lake
Harper Lake is a dry lake located in the Mojave Desert near the small community of Lockhart, California, in northwestern San Bernardino County of Southern California. The lake is accessible from Harper Lake Road, which runs north off of State Rou ...
.
["Groundwater, Rivers, Ecosystems, and Conflicts" http://waterinthewest.stanford.edu/groundwater/conflicts/index.html] In September 2014, California passed the
Sustainable Groundwater Management Act
The Sustainable Groundwater Management Act (SGMA) is a three-bill package that passed the California state legislature and was signed into California state law by Governor Jerry Brown in September 2014. Its purpose is to ensure better local and re ...
, which requires users to manage groundwater appropriately, as it is connected to surface water systems.
Colorado
Due to its arid climate, the state of
Colorado
Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
gets most of its water from underground. Because of this, there have been issues regarding groundwater engineering practices. As many as 65,000 people were affected when high levels of PFCs were found in the Widefield Aquifer. Groundwater use in Colorado dates back to before the 20th century. Nineteen of Colorado's 63 counties depend mostly on groundwater for supplies and domestic uses. The Colorado Geological Survey has three significant reports on groundwater in the Denver Basin. The first report Geology of Upper Cretaceous, Paleocene and Eocene Strata in the Southwestern Denver Basin, The second report Bedrock Geology, Structure, and Isopach Maps of the Upper Cretaceous to Paleogene Strata between Greeley and Colorado Springs, The third publication Cross Sections of the Freshwater Bearing Strata of the Denver Basin between Greeley and Colorado Springs.
New trends in groundwater engineering/hydrogeology
Since the first wells were made thousands of years ago, groundwater systems have been changed by human activity. Fifty years ago, the sustainability of these systems on a larger scale began to come into consideration, becoming one of the main focuses of groundwater engineering. New ideas and research are advancing groundwater engineering into the 21st century, while still considering groundwater conservation.
Topographical mapping
New advancements have arisen in topographical mapping to improve sustainability. Topographic mapping has been updated to include radar, which can penetrate the ground to help pinpoint areas of concern. In addition, large computations can use gathered data from maps to further the knowledge of groundwater aquifers in recent years. This has made highly complex and individualized water cycle models possible, which has helped to make groundwater sustainability more applicable to specific situations.
The role of technology
Technological improvements have advanced topographical mapping, and have also improved the quality of lithosphere, hydrosphere, biosphere, and atmosphere simulations. These simulations are useful on their own; however, when used together, they help to give an even more accurate prediction of the future sustainability of an area, and what changes can be made to ensure stability in the area. This would not be possible without the advancement of technology. As technology continues to progress, the simulations will increase in accuracy and allow for more complex studies and projects in groundwater engineering.
Growing populations
As populations continue to grow, areas which were using groundwater at a sustainable rate are now beginning to face sustainability issues for the future. Populations of the size currently seen in large cities were not taken into consideration when the long term sustainability of aquifers. These large population sizes are beginning to stress groundwater supply. This has led to the need for new policies in some urban areas. These are known as proactive land-use management, where cities can move proactively to conserve groundwater.
In Brazil, overpopulation caused municipally provided water to run low. Due to the shortage of water, people began to drill wells within the range normally served by the municipal water system. This was a solution for people in high socioeconomic standing, but left much of the underprivileged population without access to water. Because of this, a new municipal policy was created which drilled wells to assist those who could not afford to drill wells of their own. Because the city is in charge of drilling the new wells, they can better plan for the future sustainability of the groundwater in the region, by carefully placing the wells and taking growing populations into consideration.
Dependency on groundwater in the United States
In the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, 51% of the drinking water comes from groundwater supplies. Around 99% of the rural population depends on groundwater. In addition, 64% of the total groundwater of the country is used for irrigation, and some of it is used for industrial processes and recharge for lakes and rivers. In 2010, 22 percent of freshwater used in US came from groundwater and the other 78 percent came from surface water. Groundwater is important for some states that don't have access to fresh water. most of the fresh groundwater 65 percent is used for irrigation and the 21 percent is used for public purposes drinking mostly.
[Groundwater Foundation (2018). ''What is groundwater?'' http://www.groundwater.org/get-informed/basics/groundwater.html]
[Perlman, Howard, and USGS. “Groundwater Use in the United States.” Groundwater Use, the USGS Water Science School, water.usgs.gov/edu/wugw.html.]
See also
*
Environmental engineering
Environmental engineering is a professional engineering discipline that encompasses broad scientific topics like chemistry, biology, ecology, geology, hydraulics, hydrology, microbiology, and mathematics to create solutions that will protect and a ...
is a broad category hydrogeology fits into;
*
Flownet A flow net is a graphical representation of two-dimensional steady-state groundwater flow through aquifers.
Construction of a flow net is often used for solving groundwater flow problems where the geometry makes analytical solutions impractical. T ...
is an analysis tool for steady-state flow;
*
Groundwater energy balance The groundwater energy balance is the energy balance of a groundwater body in terms of incoming hydraulic energy associated with groundwater inflow into the body, energy associated with the outflow, energy conversion into heat due to friction of fl ...
: groundwater flow equations based on the energy balance;
*
Fault zone hydrogeology Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or ...
: field specifically analyzing hydrogeology in
fault zones
*
Hydrogeophysics: field integrating hydrogeology with geophysics
*
Hydrology (agriculture) Agricultural hydrology is the study of water balance components intervening in agricultural water management, especially in irrigation and drainage.
Water balance components
The water balance components can be grouped into components correspond ...
*
Isotope hydrology Isotope hydrology is a field of geochemistry and hydrology that uses naturally occurring stable and radioactive isotopic techniques to evaluate the age and origins of surface and groundwater and the processes within the atmospheric hydrologic cycle ...
is often used to understand sources and travel times in groundwater systems;
*
List of important publications in geology#Hydrogeology : important publications;
*
Oscar Edward Meinzer
Oscar Edward Meinzer (November 28, 1876 – June 14, 1948) was an American hydrogeologist who has been called the "father of modern groundwater hydrology". He was awarded the William Bowie Medal
The William Bowie Medal is awarded annually by t ...
is considered the "father of modern groundwater hydrology";
*
SahysMod SahysMod is a computer program for the prediction of the salinity of soil moisture, groundwater and drainage water, the depth of the watertable, and the drain discharge in irrigated agricultural lands, using different hydrogeologic and aquifer con ...
is a spatial agro-hydro-salinity model with groundwater flow in a polygonal network;
*
Spring (hydrology)
A spring is a point of exit at which groundwater from an aquifer flows out on top of Earth's crust (pedosphere) and becomes surface water. It is a component of the hydrosphere. Springs have long been important for humans as a source of fresh w ...
and
water supply network
A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following:
# A drainage basin (see water purification – source ...
are subjects the hydrogeologist is concerned about;
*
Water cycle
The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...
,
hydrosphere
The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
and
water resources
Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. 97% of the water on the Earth is salt water and only three percent is fresh water; slight ...
are larger concepts which hydrogeology is a part of
*
Coastal hydrogeology
References
Further reading
General hydrogeology
* Domenico, P.A. & Schwartz, W., 1998. ''Physical and Chemical Hydrogeology'' Second Edition, Wiley. — Good book for consultants, it has many real-world examples and covers additional topics (e.g. heat flow, multi-phase and unsaturated flow).
* Driscoll, Fletcher, 1986. ''Groundwater and Wells'', US Filter / Johnson Screens. — Practical book illustrating the actual process of drilling, developing and utilizing water wells, but it is a trade book, so some of the material is slanted towards the products made by Johnson Well Screens.
* Freeze, R.A. & Cherry, J.A., 1979. ''Groundwater'', Prentice-Hall. — A classic text; like an older version of Domenico and Schwartz.
* de Marsily, G., 1986. ''Quantitative Hydrogeology: Groundwater Hydrology for Engineers'', Academic Press, Inc., Orlando Florida. — Classic book intended for engineers with mathematical background but it can be read by hydrologists and geologists as well.
* Good, accessible overview of hydrogeological processes.
* Porges, Robert E. & Hammer, Matthew J., 2001. ''The Compendium of Hydrogeology'', National Ground Water Association, . Written by practicing hydrogeologists, this inclusive handbook provides a concise, easy-to-use reference for hydrologic terms, equations, pertinent physical parameters, and acronyms
* Todd, David Keith, 1980. ''Groundwater Hydrology'' Second Edition, John Wiley & Sons. — Case studies and real-world problems with examples.
* Fetter, C.W. ''Contaminant Hydrogeology'' Second Edition, Prentice Hall.
* Fetter, C.W. ''Applied Hydrogeology'' Fourth Edition, Prentice Hall.
Numerical groundwater modeling
*
Anderson, Mary P. & Woessner, William W., 1992 ''Applied Groundwater Modeling'', Academic Press. — An introduction to groundwater modeling, a little bit old, but the methods are still very applicable.
*
Anderson, Mary P., Woessner, William W., & Hunt, Randall J., 2015, ''Applied Groundwater Modeling, 2nd Edition'', Academic Press. — Updates the 1st edition with new examples, new material with respect to model calibration and uncertainty, and online Python scripts (https://github.com/Applied-Groundwater-Modeling-2nd-Ed).
* Chiang, W.-H., Kinzelbach, W., Rausch, R. (1998): Aquifer Simulation Model for WINdows – Groundwater flow and transport modeling, an integrated program. - 137 p., 115 fig., 2 tab., 1 CD-ROM; Berlin, Stuttgart (Borntraeger).
* Elango, L and Jayakumar, R (Eds.)(2001) Modelling in Hydrogeology, UNESCO-IHP Publication, Allied Publ., Chennai,
* Rausch, R., Schäfer W., Therrien, R., Wagner, C., 2005 ''Solute Transport Modelling – An Introduction to Models and Solution Strategies. - 205 p., 66 fig., 11 tab.; Berlin, Stuttgart (Borntraeger).
* Rushton, K.R., 2003, ''Groundwater Hydrology: Conceptual and Computational Models''. John Wiley and Sons Ltd.
* Wang H. F., Theory of Linear Poroelasticity with Applications to Geomechanics and Hydrogeology, Princeton Press, (2000).
* Waltham T., Foundations of Engineering Geology, 2nd Edition, Taylor & Francis, (2001).
* Zheng, C., and Bennett, G.D., 2002, ''Applied Contaminant Transport Modeling'' Second Edition, John Wiley & Sons.
Analytic groundwater modeling
*
Haitjema, Henk M., 1995. ''Analytic Element Modeling of Groundwater Flow'', Academic Press. — An introduction to analytic solution methods, especially the
Analytic element method The analytic element method (AEM) is a numerical method used for the solution of partial differential equations. It was initially developed by O.D.L. Strack at the University of Minnesota. It is similar in nature to the boundary element method (BE ...
(AEM).
* Harr, Milton E., 1962. ''Groundwater and seepage'', Dover. — a more
civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...
view on groundwater; includes a great deal on
flownet A flow net is a graphical representation of two-dimensional steady-state groundwater flow through aquifers.
Construction of a flow net is often used for solving groundwater flow problems where the geometry makes analytical solutions impractical. T ...
s.
* Kovacs, Gyorgy, 1981. ''Seepage Hydaulics'', Developments in Water Science; 10. Elsevier. -
Conformal map
In mathematics, a conformal map is a function that locally preserves angles, but not necessarily lengths.
More formally, let U and V be open subsets of \mathbb^n. A function f:U\to V is called conformal (or angle-preserving) at a point u_0\in ...
ping well explained. , (series)
* Lee, Tien-Chang, 1999. ''Applied Mathematics in Hydrogeology'', CRC Press. — Great explanation of mathematical methods used in deriving solutions to hydrogeology problems (solute transport, finite element and inverse problems too).
* Liggett, James A. & Liu, Phillip .L-F., 1983. ''The Boundary Integral Equation Method for Porous Media Flow'', George Allen and Unwin, London. — Book on BIEM (sometimes called BEM) with examples, it makes a good introduction to the method.
*
External links
International Association of Hydrogeologists— worldwide association for groundwater specialists.
UK Groundwater Forum— Groundwater in the UK
Centre for Groundwater Studies— Groundwater Education and Research.
EPA drinking water standards— the maximum contaminant levels (mcl) for dissolved species in US drinking water.
US Geological Survey water resources homepage— a good place to find free data (for both US surface water and groundwater) and free groundwater modeling software like
MODFLOW
MODFLOW is the U.S. Geological Survey modular finite-difference flow model, which is a computer code that solves the groundwater flow equation. The program is used by hydrogeologists to simulate the flow of groundwater through aquifers. The sou ...
.
US Geological Survey TWRI index— a series of instructional manuals covering common procedures in hydrogeology. They are freely available online as PDF files.
International Ground Water Modeling Center (IGWMC)— an educational repository of groundwater modeling software which offers support for most software, some of which is free.
The Hydrogeologist Time Capsule— a video collection of interviews of eminent hydrogeologists who have made a material difference to the profession.
IGRAC International Groundwater Resources Assessment Centre US Army Geospatial Center— For information on OCONUS surface water and groundwater.
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