Hydrologic Cycle Essay

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HYDROLOGIC CYCLE The hydrologic cycle is a constant movement of water above, on, and below the earth's surface. It is a cycle that replenishes ground water supplies. It begins as water vaporizes into the atmosphere from vegetation, soil, lakes, rivers, snowfields and oceans-a process called evapotranspiration. As the water vapor rises it condenses to form clouds that return water to the land through precipitation: rain, snow, or hail. Precipitation falls on the earth and either percolates into the soil or flows across the ground. Usually it does both. When precipitation percolates into the soil it is called infiltration when it flows across the ground it is called surface run off. The amount of precipitation that infiltrates, versus the…show more content…
The voids are spaces between grains of sand, or cracks in dense rock. All water beneath the land surface occurs within such void space sand is referred to as underground or subsurface water. Subsurface water occurs in two different zones. One zone, located immediately beneath the land surface in most areas, contains both water and air in the voids. This zone is referred to as the unsaturated zone. Other names for the unsaturated zone are zone of aeration and vadose zone. The unsaturated zone is almost always underlain by a second zone in which all voids are full of water. This zone is defined as the saturated zone. Water in the saturated zone is referred to as ground water and is the only subsurface water available to supply wells and springs. Water table is often misused as a synonym for ground water. However, the water table is actually the boundary between the unsaturated and saturated zones. It represents the upper surface of the ground water. Technically speaking, it is the level at which the hydraulic pressure is equal to atmospheric pressure. The water level found in unused wells is often the same level as the water table. AQUIFERS An aquifer is a saturated geologic formation that will yield a usable quantity of water to a well or spring. Ground water occurs in aquifers under two conditions: confined and unconfined. A confined aquifer is overlain by a confining bed, such as an impermeable layer of clay

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