The Hydrological Cycle

Hydrologic Cycle


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Hydrologic Cycle

The hydrologic cycle includes the following components:
 

Evaporation

  • Evapotranspiration is the combined net effect of two processes: evaporation and transpiration. Evapotranspiration uses a larger portion of precipitation than the other processes associated with the hydrologic cycle. Evaporation is the process of returning moisture to the atmosphere. Water on any surface, especially the surfaces of ponds, streams, rivers, lakes, and oceans, is warmed by the sun's heat until it reaches the point at which water turns into the vapor, or gaseous, form. The water vapor then rises into the atmosphere.
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  • Transpiration is the process by which plants return moisture to the air. Plants take up water through their roots and then lose some of the water through pores in their leaves. As hot air passes over the surface of the leaves, the moisture absorbs the heat and evaporates into the air.
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Precipitation

  • Condensation is the cooling of water vapor until it becomes a liquid. As the dew point is reached, water vapor forms tiny visible water droplets. When these droplets form in the sky and other atmospheric conditions are present, clouds will form. As the droplets collide, they merge and form larger droplets and eventually, precipitation will occur.
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  • Precipitation is moisture that falls from the atmosphere as rain, snow, sleet, or hail. Precipitation varies in amount, intensity, and form by season and geographic location. These factors impact whether water will flow into streams or infiltrate into the ground. In most parts of the world, records are kept of snow and rainfall. This allows scientists to determine average rainfalls for a location as well as classify rainstorms based on duration, intensity and average return period. This information is crucial for crop management as well as the engineering design of water control structures and flood control.
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Infiltration/Percolation

  • Infiltration is the entry of water into the soil surface. Infiltration constitutes the sole source of water to sustain the growth of vegetation and it helps to sustain the groundwater supply to wells, springs and streams. The rate of infiltration is influenced by the physical characteristics of the soil, soil cover (i.e. plants), water content of the soil, soil temperature and rainfall intensity. The terms infiltration and percolation are often used interchangeably.
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  • Percolation is the downward movement of water through soil and rock. Percolation occurs beneath the root zone. Groundwater percolates through the soil much as water fills a sponge, and moves from space to space along fractures in rock, through sand and gravel, or through channels in formations such as cavernous limestone. The terms infiltration and percolation are often used interchangeably.
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Direct Runoff

For testing support for this or other chemical or biological parameters, please contact bfenviro@ptd.net.
 



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  • Runoff is the movement of water, usually from precipitation, across the earth's surface towards stream channels, lakes, oceans, or depressions or low points in the earth's surface. The characteristics that affect the rate of runoff include rainfall duration and intensity as well as the ground's slope, soil type and ground cover.
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