Definition

• Hydrology is formed by two words: "hydro" and "logy" meaning "water" and "science".
• Hydrology is the science concerned with the occurrence, distribution, movement and properties of all the waters of the Earth.
• Hydrology is applied to major civil engineering projects such as

  (I) designing and construction of hydraulic structures for flood control, (II) dam & hydroelectric power project

  (III) water supply and drainage projects.
• Scope of Hydrology

  The maximum probable flood

  The water yield from a basin

  The ground water development

  The maximum intensity of storm and its frequency
• Journey of water from the ocean to atmosphere and back to the earth and ultimately to the ocean through the processes of evaporation, precipitation, percolation, runoff called the hydrologic cycle.
• The three fundamental processes of the hydrological cycle are

  (a) evaporation and transpiration,

  (b) precipitation

  (c) runoff.
• Evaporation is the physical process by water from free surface and land areas vaporized into the atmosphere.
• Precipitation is the product of the condensation of atmospheric water vapor that falls under gravitational into the land & oceans, includes rain, snow and other forms of water.
• Transpiration is the evaporation of water into the atmosphere from the leaves and stems of the living plants.
• Interception is the precipitation that is caught by plant surfaces and evaporates back to the atmosphere.
• Evapotranspiration is the sum of interception, transpiration, and evaporation from soils and water bodies
• Infiltration is the movement of water from the land surface to the upper layer of the soil.
• Percolation is the movement of water from one soil zone to a lower soil zone.
• Runoff is a part of precipitation which flows over ground surface or appears in surface streams, rivers, or drains.
• Ice caps and glaciers : 29,200 * 10^12 m3 > 2.14%
• Atmosphere (water vapor) 13* 10^12 m3 >0.001
• Oceans : 1,320,000* 10^12 m3 >97.3
• R= 8.314J/mol.K
• The water balance equation is given by In-Out = Delta(S) or P-Q-EV = Delta (S)
• The residence time (Tr), is the average duration for a water molecule spend in a water body/reservoir
• Residence Time (Tr) = Volume of the water/ Total flowrate