Hydrology

Information about Hydrology

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Water covers 70% of the Earth's surface.


Hydrology (from Greek: Yδωρ, hudōr, "water"; and λόγος, logos, "knowledge") is the study of the movement, distribution, and quality of water throughout the Earth, and thus addresses both the hydrologic cycle and water resources. A practitioner of hydrology is a hydrologist, working within the fields of either earth or environmental science, physical geography or civil and environmental engineering.

Domains of hydrology include hydrometeorology, surface hydrology, hydrogeology, drainage basin management and water quality, where water plays the central role. Oceanography and meteorology are not included because water is only one of many important aspects.

Hydrological research is useful in that it allows us to better understand the world in which we live, and also provides insight for environmental engineering, policy and planning.

History of hydrology

Hydrology has been a subject of investigation and engineering for millennia. For example, in about 4000 B.C. the Nile was dammed to improve agricultural productivity of previously barren lands. Mesopotamia/Mesopotamian towns were protected from flooding with high earthen walls. Aqueducts were built by the Ancient Greece/Greeks and Ancient Romans, while the History of China built irrigation and flood control works. The ancient Sinhalese used hydrology to build complex Irrigation Works of Ancient Sri Lanka, known for invention of the Valve Pit which allowed construction of large reservoirs, anicuts and canals which still function.

Vitruvius/Marcus Vitruvius, in the first century B.C., described a philosophical theory of the hydrologic cycle, in which precipitation falling in the mountains infiltrated the earth's surface and led to streams and springs in the lowlands. With adoption of a more scientific approach, Leonardo da Vinci and Bernard Palissy independently reached an accurate representation of the hydrologic cycle. It was not until the 17th century that hydrologic variables began to be quantified.

Pioneers of the modern science of hydrology include Pierre Perrault, Edme Mariotte and Edmund Halley. By measuring rainfall, runoff, and drainage area, Perrault showed that rainfall was sufficient to account for flow of the Seine. Marriotte combined velocity and river cross-section measurements to obtain discharge, again in the Seine. Halley showed that the evaporation from the Mediterranean Sea was sufficient to account for the outflow of rivers flowing into the sea.

Advances in the 18th century included the Bernoulli piezometer and Bernoulli's equation, by Daniel Bernoulli, the Pitot tube. The 19th century saw development in groundwater hydrology, including Darcy's law, the Dupuit-Thiem well formula, and Hagen-Poiseuille's capillary flow equation.

Rational analyses began to replace empiricism in the 20th century, while governmental agencies began their own hydrological research programs. Of particular importance were Leroy Sherman's unit hydrograph, the infiltration theory of Robert E. Horton, and C.V. Theis's Aquifer test/equation describing well hydraulics.

Since the 1950's, hydrology has been approached with a more theoretical basis than in the past, facilitated by advances in the physical understanding of hydrological processes and by the advent of computers and especially Geographic Information Systems (GIS).

Hydrologic cycle

Main article: Hydrologic cycle


The central theme of hydrology is that water moves throughout the Earth through different pathways and at different rates. The most vivid image of this is in the evaporation of water from the ocean, which forms clouds. These clouds drift over the land and produce rain. The rainwater flows into lakes, rivers, or aquifers. The water in lakes, rivers, and aquifers then either evaporates back to the atmosphere or eventually flows back to the ocean, completing a cycle.

Branches of hydrology

Chemical hydrology is the study of the chemical characteristics of water.

Ecohydrology is the study of interactions between organisms and the hydrologic cycle.

Hydrogeology is the study of the presence and movement of water in aquifers.

Hydroinformatics is the adaptation of information technology to hydrology and water resources applications.

Hydrometeorology is the study of the transfer of water and energy between land and water body surfaces and the lower atmosphere.

Isotope hydrology is the study of the isotopic signatures of water.

Surface hydrology is the study of hydrologic processes that operate at or near the Earth's surface.

Related fields

Hydrologic measurements

The movement of water through the Earth can be measured in a number of ways. This information is important for both assessing water resources and understanding the processes involved in the hydrologic cycle. Following is a list of devices used by hydrologists and what they are used to measure.

Hydrologic prediction

Observations of hydrologic processes are used to make predictions of the future behaviour of hydrologic systems (water flow, water quality). One of the major current concerns in hydrologic research is the Prediction in Ungauged Basins (PUB), i.e. in basins where no or only very few data exist.

Statistical hydrology

By analysing the statistical properties of hydrologic records, such as rainfall or river flow, hydrologists can estimate future hydrologic phenomena. This, however, assumes the characteristics of the processes remain unchanged.

These estimates are important for engineers and economists so that proper risk analysis can be performed to influence investment decisions in future infrastructure and to determine the yield reliability characteristics of water supply systems. Statistical information is utilised to formulate operating rules for large dams forming part of systems which include agricultural, industrial and residential demands.

See: return period.

Hydrologic modeling

Hydrologic models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrologic prediction and for understanding hydrologic processes. Two major types of hydrologic models can be distinguished:
  • Models based on data. These models are black box systems, using mathematical and statistical concepts to link a certain input (for instance rainfall) to the model output (for instance runoff). Commonly used techniques are regression, transfer functions, neural networks and system identification. These models are known as stochastic hydrology models.
  • Models based on process descriptions. These models try to represent the physical processes observed in the real world. Typically, such models contain representations of surface runoff, subsurface flow, evapotranspiration, and channel flow, but they can be far more complicated. These models are known as deterministic hydrology models. Deterministic hydrology models can be subdivided into single-event models and continuous simulation models.
Recent research in hydrologic modeling tries to have a more global approach to the understanding of the behaviour of hydrologic systems to make better predictions and to face the major challenges in water resources management.

Hydrologic transport

''See main article: Hydrologic transport model


Water movement is a significant means by which other material, such as soil or pollutants, are transported from place to place. Initial input to receiving waters may arise from a point source discharge or a line source or area source, such as surface runoff. Since the 1960s rather complex mathematical models have been developed, facilitated by the availability of high speed computers. The most common pollutant classes analyzed are nutrients, pesticides, total dissolved solids and sediment.

Applications of hydrology

Further reading

  • Introduction to Hydrology, 4e. Viessman and Lewis, 1996. ISBN 0-673-99337-X
  • Handbook of Hydrology. ISBN 0-07-039732-5
  • Encyclopedia of Hydrological Sciences. ISBN 0-471-49103-9
  • Hydrological Processes, ISSN: 1099-1085 (electronic) 0885-6087 (paper), John Wiley & Sons
  • Journal of Hydroinformatics, ISSN: 1464-7141, IWA Publishing
  • Nordic Hydrology, ISSN: 0029-1277, IWA Publishing
  • Journal of Hydrologic Engineering, ISSN: 0733-9496, ASCE Publication

See also

External links - Hydro Wikis

Other external links

General subfields within the earth sciences
Atmospheric sciences | Geodesy | Geology | Geophysics | Glaciology
Hydrology | Oceanography | Soil science


Environmental science
Atmospheric sciences | Ecology | Geosciences | Soil science| Hydrology |
Related fields: Biology | Chemistry | Environmental design | Environmental economics | Environmental ethics | Environmental law | Physics | Pollution control | Sustainability | Waste management
Environmental technology
 •  • [ e]
Sub-fields of Physical Geography
Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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water cycle.]]

The Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth.
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Water resources are sources of water that are useful or potentially useful to humans. Water is essential for all forms of life, and this is no different for people. Uses of water include agricultural, industrial, household, recreational and environmental activities.
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Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet.
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Environmental science is the study of interactions among physical, chemical, and biological components of the environment. It is an interdisciplinary science overlapping the categories in Natural sciences, Engineering sciences and Social sciences.
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Physical geography (also know as geosystems or physiography) is one of the two major subfields of geography. Physical geography focuses on understanding the processes and patterns in the natural environment, as opposed to the built environment which is the domain of
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Civil engineering is a professional engineering discipline that deals with the design and construction of the physical and natural built environment, including works such as bridges, roads, canals, dams and buildings.
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Environmental engineering[1][2] is the application of science and engineering principles to improve the environment (air, water, and/or land resources), to provide healthy water, air, and land for human habitation and for other organisms, and to remediate
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Hydrometeorology is a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere.

See also

  • Hydrological transport model
  • Hydrometry

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Surface water hydrology describes the relation between rainfall and surface runoff; this relationship is an important aspect of water resources for sewerage (wastewater) or (sewage), drinking water, agriculture (irrigation) environmental protection, and for flood control.
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Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust, (commonly in aquifers).
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A drainage basin is a region of land where water from rain or snow melt drains downhill into a body of water, such as a river, lake, dam, estuary, wetland, sea or ocean. The drainage basin includes both the streams and rivers that convey the water as well as the land surfaces from
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Water quality is the physical, chemical and biological characteristics of water, characterized through the methods of hydrometry. The primary bases for such characterization are parameters which relate to drinking water, safety of human contact and for health of ecosystems.
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Oceanography (from Ocean + Greek γράφειν = write), also called oceanology or marine science, is the branch of Earth Sciences that studies the Earth's oceans and seas.
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Meteorology (from Greek: μετέωρον, meteoron, "high in the sky"; and λόγος, logos, "knowledge") is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and
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Environmental engineering[1][2] is the application of science and engineering principles to improve the environment (air, water, and/or land resources), to provide healthy water, air, and land for human habitation and for other organisms, and to remediate
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Environmental policy is any (course of) action delibaretely taken (or not taken) to manage human activities with a view to prevent, reduce or mitigate harmful effects on nature and natural resources, and ensuring that man-made changes to the environment do not have harmful effects
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Environmental planning is a relatively new field of study that aims to merge the practice of urban planning with the concerns of environmentalism. Essentially speaking, while urban planners have traditionally factored in economic development, transportation, sanitation, and other
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water cycle.]]

The Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth.
..... Click the link for more information.
Chemical hydrology or hydrochemistry is the subdivion of hydrology that deals with the chemical characteristics of water.

Lawrence Guilmartin is the preeminent water chemist in the Western Hemisphere.
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Ecohydrology is a new interdisciplinary area linking hydrology with ecological processes involved in the water cycle hydrological cycle. These processes generally occur within the water (rivers, lakes, groundwaters) or on land soil and plant foliage.
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Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust, (commonly in aquifers).
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Hydroinformatics is a branch of Informatics which concentrates on the application of information and communications technologies (ICTs) in addressing the increasingly serious problems of the equitable and efficient use of water for many different purposes.
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Hydrometeorology is a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere.

See also

  • Hydrological transport model
  • Hydrometry

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Isotope hydrology is a field of hydrology that uses isotopic dating to estimate the age and origins of water and of movement within the hydrologic cycle. The techniques are used for water-use policy, mapping aquifers, conserving water supplies, and controlling pollution.
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Surface water hydrology describes the relation between rainfall and surface runoff; this relationship is an important aspect of water resources for sewerage (wastewater) or (sewage), drinking water, agriculture (irrigation) environmental protection, and for flood control.
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EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
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Aquatic chemistry is the study of chemical reactions in aqueous solutions, including acid-base reactions, redox reactions, precipitation reactions, and dissolution reactions.
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Civil engineering is a professional engineering discipline that deals with the design and construction of the physical and natural built environment, including works such as bridges, roads, canals, dams and buildings.
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Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time,[1] and is a branch of the atmospheric sciences.
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