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study of water and its properties, including its distribution and movement in and through the land areas of the earth. The hydrologic cycle consists of the passage of water from the oceans into the atmosphere by evaporation and transpiration (or evapotranspiration), onto the lands, over and under the lands as runoff and infiltration, and back to the oceans. Hydrology is principally concerned with the part of the cycle after the precipitation of water onto the land and before its return to the oceans; thus meteorologymeteorology,
branch of science that deals with the atmosphere of a planet, particularly that of the earth, the most important application of which is the analysis and prediction of weather.
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 and oceanographyoceanography,
study of the seas and oceans. The major divisions of oceanography include the geological study of the ocean floor (see plate tectonics) and features; physical oceanography, which is concerned with the physical attributes of the ocean water, such as currents and
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 are closely related to hydrology. Hydrologists study the cycle by measuring such variables as the amount and intensity of precipitation, the amount of water stored as snow or in glaciers, the advance and retreat of glaciers, the rate of flow in streams, and the soil-water balance. Hydrology also includes the study of the amount and flow of groundwater. Though the flow of water cannot be seen under the surface, hydrologists can deduce the flow by understanding the characteristics, including permeability, of the soil and bedrock; how water behaves near other sources of water, such as rivers and oceans; and fluid flow models based on water movements on the earth's surface. Hydrology is also important to the study of water pollution, especially of groundwater and other potable water supplies. Knowledge of hydrology is extensively used to determine the movement and extent of contamination from landfills, mine runoff, and other potentially contaminated sites to surface and subsurface water. See water supplywater supply,
process or activity by which water is provided for some use, e.g., to a home, factory, or business. The term may also refer to the supply of water provided in this way.
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The science of water relating to the occurrence, properties, distribution, circulation, and transport of water.



the science that studies natural waters and the phenomena and processes occurring in them. As a geophysical science, hydrology is in close contact with the sciences of geographic, geologic, and biological cycles.

The subject matter of hydrology is bodies of water—that is, oceans, seas, rivers, lakes, reservoirs, swamps, and accumulations of moisture in the form of snow cover, glaciers, and soil and subterranean waters. The main problems of present-day hydrology are to investigate the hydrologic cycle and the influence on it of human activity, as well as the control of the regimen of bodies of water and the stream-flow regimen of territories; to perform space-time analyses of hydrologic elements (water level, discharge, temperature, and so on) for individual territories and the earth as a whole; and to discover patterns in the variations of these elements. The principal practical application of hydrology is in the evaluation of the present state of water resources, in forecasting their future state, and in laying the basis for their rational utilization.

Based on the specific characteristics of bodies of water and of the methods of their study, hydrology is divided into oceanography (hydrology of the sea), land hydrology (hydrology proper; more precisely, hydrology of the surface water of land), and hydrogeology (hydrology of subterranean water).

Hydrology initially developed as a branch of physical geography, hydraulic engineering, geology, and navigation and took shape as a system of scientific knowledge only at the beginning of the 20th century. A definition of hydrology as a science was provided by V. G. Glushkov in 1915. A large role in the formation of hydrology was played by the establishment in 1919 of the State Hydrologic Institute. Present-day hydrology makes wide use of methods employed in geography, physics, and other sciences, and the role of mathematical methodology is steadily increasing.


Glushkov, V. G. Voprosy teorii i melody gidrologic he skikh issledovanii. Moscow, 1961.
Kalinin, G. P. Problemy global’noi gidrologii. Leningrad, 1968.
Sokolov, A. A., and A. I. Chebotarev. Ocherki razvitiia gidrologii v SSSR. Leningrad, 1970.
Chebotarev, A. I. Obshchaia gidrologiia (vody sushi). Leningrad, 1960.



the study of the distribution, conservation, use, etc., of the water of the earth and its atmosphere, particularly at the land surface
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On April 21, Minera Yanacocha said in a press release that it will undertake a new evaluation of technical and economic alternatives for the project, as well as of ways to compensate for its hydrologic and environmental impact.
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The wealth of hydrologic and water quality data accompanied by management practice information also contributed to the development of hydrologic and water quality models such as EPIC/APEX, GLEAMS, and SWAT.
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This study was designed to examine leaf height, leaf density, biomass, nutrient content of the mature leaves, and the ratio between below-ground and above-ground biomasses in two floodplain lakes with different degree of connectivity under different hydrologic condition to answer the following questions.