Hydrology

Water covers 70% of the Earth's surface.

Hydrology (from Greek: Yδρoλoγια, Yδωρ+Λoγos, Hydrologia, the "study of water") 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.

Hydrologic cycle

Main article: Hydrologic 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.

Hydromorphology

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

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

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
• 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 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.

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

• Mitigating and predicting flood, landslide and drought risk;
• 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 modelling

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

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