Hydrology

Water covers 70% of the Earth's surface.

Hydrology (from the Greek word Yδρoλoγια, hydrologia, the "study of water") is the study of the movement, distribution, and quality of water throughout the Earth. It addresses both the hydrologic cycle and water resources. A practitioner of hydrology, or hydrologist, may work in any of several fields: earth science, environmental science, physical geography, civil engineering, and environmental engineering.

Hydrological research is useful in that it allows engineers to (a) design irrigation schemes, water-supply systems, dams, bridges, and sewers; (b) predict and mitigate the risk of floods, droughts, landslides, erosion, and sedimentation; and (c) assess the risk of contaminant transport. In this manner, it provides insights for environmental engineering, policy, and planning.

Branches of hydrology

Chemical hydrology is the study of the chemical characteristics of water. It examines how water is affected as it comes into contact with different materials on and within the Earth's surface. This field includes studies on the mechanics by which salts are transported from land to sea via runoff or erosion, and from ocean back to land, by the process of evaporation and precipitation. Through examining the chemical characteristics of bodies of water in specific regions, researchers can also determine the date and origin of groundwater in present-day desert regions, glaciers, and ice sheets. <"Chemical Hydrology." Encyclopedia Britannica Online, 2006. http://www.britannica.com/ebc/article-9360468>

Ecohydrology is the study of the relationship between the hydrological system and the ecological processes that are affected by it. Ecological processes include biota living on and within the soil. Ecohydrologists study how the hydrological system affects plant physiology, soil moisture, and plant diversity and spatial orientation in various regions over a period of time. Ecohydrology determines the water balance in a point in the landscape. It has four main components including, infiltration of precipitation into the soil, evapotranspiration, leakage of water into deeper portions of the soil not accessible to the plant, and runoff from the ground surface. <parts copied from ecohydrology article in wiki>

Hydrogeology is the study of the presence and movement of water in aquifers. It involves the study of the distribution and movement of groundwater in the porous layers of rock, sand, and gravel below the Earth's surface as it moves down its energy gradient. Groundwater typically travels throughout aquifers, or porous material that allows sufficient quantities of water to flow into wells or springs. Hydrogeology examines the rate of diffusion of water through porous media by using Darcey's Law and Laplace equations. The terms geohydrology and hydrogeology are often used interchangeably, demonstrating one example of the interdisciplinary nature of the subject. <Todd, David Keith. Groundwater Hydrology. 2nd Ed. New York: John Wiley & Sons, 1980.> & <"Hydrogeology" in Wiki>

Hydroinformatics is the adaptation of information technology to hydrology and water resources applications. It combines the study of hydrology with information technology in order to facilitate decision-making on many critical applications. Hydrological data are collected, stored, processed and analyzed using modeling techniques and simulations, based on the knowledge of particular systems. Three common hydrological data collected include the rate of flow of major rivers and streams, precipitation, and water height in wells. <"Hydroinformatics" on Wiki> & <Soh, Leen-kiat et al. "A Task-Based Approach to User Interface Design for a Web-Based Hydrologic Information Systems." Transactions in GIS. Vol 10 (3). Blackwell Synergy, May 2006.>

Hydrometeorology is the study of the transfer of water and energy between land and water body surfaces and the lower atmosphere. Hydrometeorology combines the two areas of meteorology, or the study of the atmosphere and the moevement of water as liquid and vapor in the air, and hydrology by encorporating meteorology to solve hydrological problems. These problems include forcasting flood or drought, or determining water resources and the safety of dams. Hydrometeorologists try to determine, through empirical data or theoretically, how the dynamics of water in the atmosphere affect the greatest levels of precipitation reaching the ground. The domain of hydrometeorology in the physical sciences is not very clearly defined, as it involves cloud physics, climatology, weather forecasting, and hydrology, to name a few. <The Hydrometeorology Associates. http://www.hydrometeorology.com/> & <Bruce, J.P. et al. Introduction to Hydrometeorology. London: Pergamon Press, 1966.>

Hydromorphology: is the study of the physical characteristics of bodies of water on the Earth's surface, including river basins, channels, streams, and lakes. Water quality, levels of pollution, and biological components needed for ecological system maintenance are a few areas assessed when classifying water systems. Hydromorphology studies the dynamics of groundwater flow into channels, lakes, and streams. It measures flow patterns and geometry as well as routing flows to avoid flooding or drought. <Ward, Andy D. and William J. Elliot. Environmental Hydrology. Boca Raton: Lewis Publishers, 1995.>

Isotope hydrology is the study of the isotopic signatures of water. It is a field of hydrology that utilizes isotopic dating to determine the origin and age of water throughout it's movement within the hydrological cycle. Isotopic dating involves measuring the levels of deviation in the number of neutrons (isotopes)of oxygen and hydrogen, which compose water. Researchers are able to determine groundwater dated back to as old as the ice age by using these techniques. Isotope hydrology deals with water usage policy, mapping aquifers, conservation of water resources and maintaining pollution levels. One way isotopic hydrology is applied today is in the mitigation of arsenic levels in the drinking water of Bangledesh. <"Isotope Hydrology" from Wiki>

Surface hydrology is the study of bodies of water on or near the Earth's surface. Rivers, dams, lakes, and reservoirs are all included in this area of study, including the systems used in recreational activity and transportation. Surface hydrology addresses issues pertaining to eroding soils and streams due to surface flow. Flooding, nutrient runoff, and pollutants are a few of the effects addressed, as well as the destruction of civil constructions like dams. Methods of hydraulic and hydrologic design regulation are also undertaken in this field of study, as researchers simulate the long and short term effects of anthropogenically manipulated surface water forms. <Ward, Andy D. and William J. Elliot. Environmental Hydrology. Boca Raton: Lewis Publishers, 1995.>

Related fields

• Aquatic chemistry: Aquatic chemistry studies chemical reactions in aqueous solutions, including acid-base reactions, oxidation- reduction reactions, precipitation reactions, and dissolution reactions. It can be applied to addressing issues on water pollution and treatment and creating sustainable methods of production with little environmental impact. <"Aquatic Chemistry" from Wiki>

• Civil engineering: Related to the study of hydrology, civil engineers contribute in the planning, design, construction, and maintenance of structures related to hydraulics, for instance in controlling water flow by way of draining swamps, municipal sewage disposal, flood control and irrigation. They also work in creating structures that help route water flow in dams and bridges. <"Engineering Terms: Civil Engineering." Michael's Design. http://www.angelfire.com/biz7/michaelsdesign/EngineeringTerms.html>

• Climatology: Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences. Average precipitation and temperature trends are measured over specific regions. <from climatology article in wiki>

• Environmental engineering: Environmental engineering combines science and engineering principles to address ways in which to improve the quality of air, land, and water for living organisms. Chemical, biological, and geological sciences are incorporated into the techniques of mechanical, civil, and chemical engineering to address issues of public health and policy. Remediation of polluted sites, sanitary engineering, waste reduction and prevention are keys areas of concern. <"Environmental Engineering." Dictionary by LaborLawTalks. http://dictionary.laborlawtalk.com/Environmental_engineering> & <"Environmental Engineering" from Wiki>

• Physical Geography: Physical geography deals with topics concerning the Earth's surface, including glaciers, landforms, rivers and oceans, climate, and hydrological processes driven by the sun. It involves the systemic study of patterns within the biosphere, lithosphere, hydrosphere, and atmosphere. <parts from physical geography in wiki>

• Geomorphology: Geomorphology is the study of landforms, including their origin and evolution, and the processes that shape them. A combination of field observation, physical experiment, and numerical modeling help geomorphologists to understand landform history and dynamics, and predict future changes. Applications of geomorphology include landslide prediction and mitigation, river control and restoration, coastal protection, and assessing the presence of water on Mars. <Geomorpholgy article from wiki>

• Hydraulic engineering: Hydraulic engineering is a sub-discipline of civil engineering that focuses on the flow and conveyence of fluids, particularly water. It involves the design and construction of hydraulic structures, like bridges, dams, canals, channels, and levees, and also aligns itself with the goals of sanitary and environmental engineering. <"Hydraulic Engineering" from Wiki>

• Limnology: Limnology involves the study of inland waters (both saline and fresh), specifically lakes, ponds and rivers (both natural and manmade), including their biological, physical, chemical, and hydrological aspects. <"limnology" from wiki>

• Oceanography: Oceanography is the study of the Earth's seas and oceans. It includes the geological movement of tectonic plates under the Earth's surface, physical oceanographic characteristics, chemical processes, and marine biology taking place within these bodies of water. <"Oceanography" from Wiki>

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.

• 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 gauge - rain and snowfall
• Satellite- topographic patterns of surface water
• Sling psychrometer - humidity
• Stream gauge - stream flow (see: discharge (hydrology))
• Tensiometer - soil moisture
• Time domain reflectometer - soil moisture

Hydrologic prediction

Observations of hydrologic processes are used to make predictions of future water movement and quantity.

Statistical hydrology

By analyzing 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 for future investment decisions in infrastructure and to determine the yield reliability characteristics of water supply systems. Statistical information is utilized to formulate operating rules for large dams forming part of systems which include agricultural, industrial and residential demands.

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.

Hydrologic transport

Water movement is a significant means by which other material, such as soil or pollutants, are transported from place to place. Initial input of 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

• Mitigating and predicting the risk of flood, landslide, and drought.
• Designing irrigation schemes and managing agricultural productivity.
• Providing drinking water.
• Designing dams for water supply or hydroelectric power generation.
• Designing bridges.
• Designing sewers and urban drainage system.
• Analyzing the impacts of antecedent moisture on sanitary sewer systems.
• Predicting geomorphological changes, such as erosion or sedimentation.
• Assessing the impacts of natural and anthropogenic environmental change on water resources.
• Assessing contaminant transport risk and establishing environmental policy guidelines.

References

ISBN links support NWE through referral fees

• 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

External links

• International Glossary of Hydrology.
• U.S. Geological Survey - Water Resources of the United States
• British Hydrology Society
• Institute of Hydrology, Albert-Ludwigs-University of Freiburg, Germany
• NOAA's National Weather Service - Office of Hydrologic Development
• Virtual Campus in Hydrology and Water Resources
• Decision tree to choose an uncertainty method for hydrological and hydraulic modeling

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

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