Water covers 70% of the Earth's surface.

Hydrology (from Greek: Yδωρ, hudōr, "water"; and λόγος, logos, "study") is the study of the movement, distribution, and quality of water throughout the Earth, and thus addresses both the hydrologic cycle and water resources. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 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 Water resources are sources of Water that are useful or potentially useful to Humans Uses of water include Agricultural, industrial, Household A practitioner of hydrology is a hydrologist, working within the fields of either earth or environmental science, physical geography or civil and environmental engineering. Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet Environmental science is the study of interactions among physical chemical and biological components of the environment. Physical geography (also known as geosystems or physiography) is one of the three major subfields of Geography. Civil engineering is a professional engineering discipline that deals with the design construction and maintenance of the physical and naturally built Environmental engineering is the application of Science and Engineering principles to improve the environment (air water and/or land resources

Domains of hydrology include hydrometeorology, surface hydrology, hydrogeology, drainage basin management and water quality, where water plays the central role. Hydrometeorology is a branch of Meteorology and Hydrology that studies the transfer of Water and Energy between the land surface and the lower Surface water Hydrology is a field that encompasses all surface waters of the globe (overland flows rivers lakes wetlands estuaries oceans etc Hydrogeology ( hydro- meaning water and -geology meaning the study of the Earth) is the area of Geology that deals with the distribution and A drainage basin is an extent of Land where Water from Rain or Snow melt drains downhill into a body of water such as a River, Water quality is the physical chemical and biological characteristics of Water in relationship to a set of standards Oceanography and meteorology are not included because water is only one of many important aspects. Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write also called oceanology or Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary

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. Environmental engineering is the application of Science and Engineering principles to improve the environment (air water and/or land resources Environmental policy is any (course of action deliberately taken (or not taken to manage human activities with a view to prevent reduce or mitigate harmful effects on nature and natural Environmental planning is a field of study that since the 1970s has been sconcerned with a given society's collective stewardship over its resources that ultimately includes those of the

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. Mesopotamian towns were protected from flooding with high earthen walls. Mesopotamia (from the Greek meaning "land between the rivers" is an area geographically located between the Tigris and Euphrates rivers largely corresponding Aqueducts were built by the Greeks and Ancient Romans, while the History of China shows they built irrigation and flood control works. An aqueduct is an artificial channel that is constructed to convey water from one location to another The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca This is a list of topics related to ancient Rome that aims to include aspects of both the ancient Roman Republic and Roman Empire. Chinese civilization originated in various city-states along the Yellow River ( valley in the Neolithic era The ancient Sinhalese used hydrology to build complex irrigation Works in Sri Lanka, also known for invention of the Valve Pit which allowed construction of large reservoirs, anicuts and canals which still function. Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka ( Sinhalese:, இலங்கை known as Ceylon before 1972 is an Island A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees

Marcus Vitruvius, in the first century B. Marcus Vitruvius Pollio (born c 80–70 BC died after c 15 BC was a Roman Writer, Architect and Engineer (possibly praefectus fabrum 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. Leonardo di ser Piero da Vinci ( April 15 1452 – May 2 1519 was an Italian Polymath, having been a scientist Mathematician, Engineer Bernard Palissy (c 1510 - c 1589 was a French potter and craftsman famous for having struggled for 16 years to imitate Chinese porcelain. 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. Edme Mariotte (c 1620 - 12 May 1684) was a French Physicist and priest Edmond Halley FRS (ˈɛdmənd ˈhɔːlɪ ( November 8, 1656 &ndash January 14, 1742) was an English Astronomer 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. Bernoulli can refer to any one or more of the Bernoulli family of Swiss mathematicians in the eighteenth century including Daniel Bernoulli A piezometer is a small diameter Water well used to measure the Hydraulic head of Groundwater in Aquifers Similarly it may also be a standpipe A Pitot (ˈpiːtoʊ tube is a Pressure measurement instrument used to measure Fluid flow Velocity. The 19th century saw development in groundwater hydrology, including Darcy's law, the Dupuit-Thiem well formula, and Hagen-Poiseuille's capillary flow equation. Jean Louis Marie Poiseuille \pwä-'zəi\ ( April 22, 1799 - December 26, 1869) was a French Physician and Physiologist

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 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 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. Chemical hydrology or hydrochemistry is the subdivion of Hydrology that deals with the chemical characteristics of Water.

Ecohydrology is the study of interactions between organisms and the hydrologic cycle. Ecohydrology (from Greek grc οἶκος oikos, "house(hold" grc ὕδωρ hydōr, "water" and grc -λογία -logia

Hydrogeology is the study of the presence and movement of water in aquifers. Hydrogeology ( hydro- meaning water and -geology meaning the study of the Earth) is the area of Geology that deals with the distribution and

Hydroinformatics is the adaptation of information technology to hydrology and water resources applications. Hydroinformatics is a branch of Informatics which concentrates on the application of information and communications technologies (ICTs in addressing the increasingly

Hydrometeorology is the study of the transfer of water and energy between land and water body surfaces and the lower atmosphere. Hydrometeorology is a branch of Meteorology and Hydrology that studies the transfer of Water and Energy between the land surface and the lower

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

Surface hydrology is the study of hydrologic processes that operate at or near the Earth's surface. Surface water Hydrology is a field that encompasses all surface waters of the globe (overland flows rivers lakes wetlands estuaries oceans etc EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Related fields

• Aquatic chemistry
• Civil engineering
• Climatology
• Environmental engineering
• Geomorphology
• Hydrography
• Hydraulic engineering
• Limnology
• Oceanography
• Physical Geography

Hydrologic measurements

The movement of water through the Earth can be measured in a number of ways. Aquatic chemistry is the study of chemical reactions in aqueous Solutions including acid-base reactions, redox reactions, precipitation reactions Civil engineering is a professional engineering discipline that deals with the design construction and maintenance of the physical and naturally built Climatology (from Greek grc κλίμα klima, "region zone" and grc -λογία -logia) is the study of Climate, scientifically Environmental engineering is the application of Science and Engineering principles to improve the environment (air water and/or land resources Geomorphology (from Greek: γη ge, "earth" μορφή morfé, "form" and λόγος Logos, "knowledge" Hydrography focuses on the measurement of physical characteristics of Waters and marginal land Hydraulic engineering is a sub-discipline of Civil engineering concerned with the flow and conveyance of Fluids principally Water. Limnology (from Greek Λίμνη limne, "lake" and λόγος logos, "knowledge" is the division of Hydrology that studies inland Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write also called oceanology or Physical geography (also known as geosystems or physiography) is one of the three major subfields of Geography. 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.

• Disdrometer - precipitation characteristics
• Evaporation -Symon's evaporation pan
• Infiltrometer - infiltration
• Piezometer - groundwater pressure and, by inference, groundwater depth (see: aquifer test)
• Radar - cloud properties, rain rate estimation, hail and snow detection
• Rain gauge - rain and snowfall
• Satellite - rainy area identification, rain rate estimation, land-cover/land-use, soil moisture
• Sling psychrometer - humidity
• Stream gauge - stream flow (see: discharge (hydrology))
• Tensiometer - soil moisture
• Time domain reflectometer - soil moisture
• Capacitance probe-soil moisture

Hydrologic prediction

Observations of hydrologic processes are used to make predictions of the future behaviour of hydrologic systems (water flow, water quality). A disdrometer is an instrument used to measure the drop size distribution and Velocity of falling hydrometeors. Evaporation is the process by which Molecules in a Liquid state (e Pan evaporation is a measurement that combines or integrates the effects of several climate elements temperature humidity solar radiation and wind Infiltrometer is a device used to measure the rate of water infiltration into Soil or other porous media A piezometer is a small diameter Water well used to measure the Hydraulic head of Groundwater in Aquifers Similarly it may also be a standpipe An aquifer test (or a pumping test) is conducted to evaluate an Aquifer by "stimulating" the aquifer through constant Pumping and observing the Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships A rain gauge (also known as a udometer or a pluviometer or a cup) is a type of instrument used by meteorologists and Hydrologists This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Hygrometers are instruments used for measuring Humidity. A simple form of a hygrometer is specifically known as a "psychrometer" and consists of two Thermometers A stream gauge, or stream gage, refers to a site along a Stream where measurements of volumetric discharge (flow are made In Hydrology, the discharge or outflow of a River is the volume of Water transported by it in a certain amount of time A tensiometer is a device used to determine matric water potential \Psi_m ( Soil moisture tension in the Vadose zone. Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, A time-domain reflectometer ( TDR) is an electronic instrument used to characterize and locate faults in metallic cables (for example twisted wire pairs, Coaxial Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, Capacitance sensors use Capacitance to measure the Dielectric Permittivity of a surrounding medium Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, A prediction is a statement or claim that a particular Event will occur in the Future in more certain terms than a forecast. 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. Statistics is a mathematical science pertaining to the collection analysis interpretation or explanation and presentation of Data. 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. An engineer is a person professionally engaged in a field of Engineering. An economist is an expert in the Social science of Economics. Statistical information is utilised to formulate operating rules for large dams forming part of systems which include agricultural, industrial and residential demands. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture For other uses of this term see Industry (disambiguation An industry (from Latin industrius, "diligent industrious" Within a urban area there is a tendency for land uses to Aggregate.

See: return period. A return period also known as a recurrence interval is an estimate of the interval of time between events like an Earthquake, Flood or river discharge

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). Black box is a technical term for a device or system or object when it is viewed primarily in terms of its input and output characteristics Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to RUNOFF was the first Computer Text formatting program to see significant use Commonly used techniques are regression, transfer functions, neural networks and system identification. A transfer function is a mathematical representation in terms of spatial or temporal frequency of the relation between the input and output of a ( linear time-invariant) Traditionally the term neural network had been used to refer to a network or circuit of biological neurons. System identification is a general term to describe mathematical Tools and Algorithms that build dynamical models from measured data 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. Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Subsurface flow is the flow of water beneath ground surface in Hydrology. Evapotranspiration (ET is a term used to describe the sum of Evaporation and Plant Transpiration from the earth's land surface to Atmosphere The Manning formula, known also as the Gauckler-Strickler formula in Europe is an Empirical formula for open channel flow or flow driven by Gravity. 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. In Hydrology, behavioral modeling is a modeling approach that focuses on the modeling of the behavior of hydrological Systems The behavioral

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. An hydrological transport model is a Mathematical model used to simulate river or Stream flow and calculate water quality parameters Initial input to receiving waters may arise from a point source discharge or a line source or area source, such as surface runoff. A point source of pollution is a single identifiable localized source of air, water, thermal, noise or light Pollution A line source is a source of air noise water contamination or electromagnetic radiation that emanates from a linear (one-dimensional geometry Area sources are sources of pollution which emit a substance or radiation from a specified area Surface runoff is a term used to describe when soil is infiltrated to full capacity and excess Water, from Rain, Snowmelt, or other sources flows Since the 1960s rather complex mathematical models have been developed, facilitated by the availability of high speed computers. Note The term model has a different meaning in Model theory, a branch of Mathematical logic. The most common pollutant classes analyzed are nutrients, pesticides, total dissolved solids and sediment. A nutrient is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment A pesticide is a substance or mixture of substances used to kill a pest. Total Dissolved Solids (often abbreviated TDS) is an expression for the combined content of all Inorganic and organic substances contained in a liquid Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of

Applications of hydrology

• Determining the water balance of a region. Note The Water Balance method is also a winding mechanism used in mining In Hydrology, a water balance Equation can be used to describes
• Designing riparian restoration projects.
• Mitigating and predicting flood, landslide and drought risk. A flood is an overflow of an expanse of water that submerges land a deluge A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur A drought is an extended period of months or years when a region notes a deficiency in its water supply
• Real-time flood forecasting and flood warning. Flood forecasting is the use of real-time precipitation and Streamflow data in rainfall-runoff and Streamflow routing models to forecast flow Flood warning is closely linked to the task of Flood forecasting.
• Designing irrigation schemes and managing agricultural productivity. Irrigation is an artificial application of water to the soil usually for assisting in growing crops Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture
• Part of the hazard module in catastrophe modeling. This article refers to the use of computers to estimate losses caused by disasters
• Providing drinking water. Water of sufficient quality to serve as drinking water is termed potable water whether it is used for drinking or not
• Designing dams for water supply or hydroelectric power generation. A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees Water supply is the process of self-provision or provision by third parties of water of various qualities to different users Hydroelectricity is electricity generated by Hydropower, ie the production of power through use of the gravitational force of falling water
• Designing bridges. A bridge is a Structure built to span a Gorge, Valley, Road, railroad track, River, Body of water
• Designing sewers and urban drainage system.
• Analyzing the impacts of antecedent moisture on sanitary sewer systems. Antecedent moisture is a term from the fields of Hydrology and Sewage collection and disposal that describes the relative wetness or dryness of a watershed
• Predicting geomorphological changes, such as erosion or sedimentation. Geomorphology (from Greek: γη ge, "earth" μορφή morfé, "form" and λόγος Logos, "knowledge" Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Sedimentation describes the motion of Molecules in Solutions or particles in suspensions in response to an external force such as gravity
• Assessing the impacts of natural and anthropogenic environmental change on water resources. Water resources are sources of Water that are useful or potentially useful to Humans Uses of water include Agricultural, industrial, Household
• Assessing contaminant transport risk and establishing environmental policy guidelines. Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in

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
• Hydrologic Analysis and Design by McCuen, Third Edition, 2005 ISBN 0-13-142424-6

See also

• Hydropower
• International Hydrological Programme
• Water cycle
• Water distribution on Earth
• Water management

External links

Other On-line Resources

• International Glossary of Hydrology. John Wiley & Sons Inc, also referred to as Wiley, is a global Publishing company that markets its products to professionals and consumers students and instructors The Journal of Hydrologic Engineering is a bimonthly Engineering journal that was first published by the American Society of Civil Engineers in 1996 Hydropower, hydraulic power or water power is power that is derived from the Force or Energy of moving water which may The International Hydrological Programme is a United Nations organization subsidiary to EcoSoc which focuses on the use and availability of water 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 This article is an overview of the distribution of Water on Earth. Water management is the practices of planning developing distribution and optimum utilizing of water resources under defined water polices and regulations
• Virtual Campus in Hydrology and Water Resources
• Decision tree to choose an uncertainty method for hydrological and hydraulic modelling

National and International Research Bodies

• U.S. Geological Survey - Water Resources of the United States
• Centre for Ecology and Hydrology - UK
• eawag - aquatic research, ETH Zürich, Switzerland
• Institute of Hydrology, Albert-Ludwigs-University of Freiburg, Germany
• NOAA's National Weather Service - Office of Hydrologic Development
• National Hydrology Research Center - Canada

National and International Societies

• International Association of Hydrological Sciences (IAHS)
• British Hydrological Society
• Russian Geographical Society (Moscow Centre) - Hydrology Commission
• International Assoc for Environmental Hydrology
• American Water Resources Association

Basin- and Catchment-wide Overviews

• Connected Waters Initiative, University of New South Wales — Investigating and raising awareness of groundwater and water resource issues in Australia