Water penetrates the ground through joints or small pore spaces between particles via a process known as infiltration. The water contained in spaces within bedrock and regolith is referred to as Groundwater.
The uppermost layer is the unsaturated zone that may contain some water but is not saturated. This is known as the zone of aeration. The saturated zone lies below the zone of aeration and is the layer where the pores of the soil or rock are completely filled with water. Groundwater passes through soil, regolith and rock by way of open pore spaces between grains or fractures. Permeability is a measure of how easily a rock allows fluids to pass through it. Sandstone typically more permeable than clays.
The Specific Yield refers to that portion of groundwater that will drain under the influence of gravity and therefore is available for use. The Specific Retention refers to that portion of the groundwater that remains bound in the material and is unable to pass through it. The movement of groundwater in the saturated zone is termed percolation. Water moves slowly by percolation through very small pores along parallel, threadlike paths.
Upward flow beneath streams or lakes is due to water being under greater pressure beneath a hill than beneath a stream. Water flows towards areas of lower pressure. The water in a reservoir is very slow moving compared to the river.
Therefore, the majority of the sediments that the river was carrying settle to the bottom of the reservoir. A reservoir will eventually fill up with sediment and mud and become unusable. The hydrologic cycle or water cycle is a graphic representation of how water is recycled through the environment. Water molecules remain constant, though they may change between solid, liquid, and gas forms.
Drops of water in the ocean evaporate, which is the process of liquid water becoming water vapor. Evaporation can occur from water surfaces, land surfaces, and snow fields into the air as water vapor.
Moisture in the air can condensate, which is the process of water vapor in the air turning into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation. Water vapor condenses on tiny particles of dust, smoke, and salt crystals to become part of a cloud.
After a while, the water droplets combine with other droplets and fall to Earth in the form of precipitation rain, snow, hail, sleet, dew, and frost.
Once the precipitation has fallen to Earth, it may go into an aquifer as groundwater or the drop may stay above ground as surface water. The hydrologic cycle is an important concept to understand. Water has so many uses on Earth, such as human and animal consumption, power production, and industrial and agricultural needs.
Precipitation—in the form of rain and snow—also is an important thing to understand. It is the main way that the water in the skies comes down to Earth, where it fills the lakes and rivers, recharges the underground aquifers, and provides drinks to plants and animals.
Different amounts of precipitation fall on different areas of the Earth at different rates and at various times of the year. One problem facing the cycle of water on Earth is water contamination. Chemicals that go into the water often are very difficult, if not impossible, to remove. One potential source of contamination of water is runoff, the overland flow of water.
While precipitation causes the runoff to occur, stripping vegetation from land can add to the runoff in a particular area. The sediment and soil from these areas, not to mention any pesticides or fertilizers that are present, are washed into the streams, oceans, and lakes. What happens to the rain after it falls depends on many factors, such as the intensity and duration of rainfall, the topography of the land, soil conditions, amount of urbanization, and density of vegetation.
A common misconception about rain that it is tear-shaped, when in actuality it is shaped more like a hamburger bun. Rain drops also are different sizes, due to the initial difference in particle size and the different rate of coalescence. Glaciers and icecaps are referred to as storehouses for fresh water. They cover 10 percent of the world's land mass. These glaciers are primarily located in Greenland and Antarctica. The glaciers in Greenland almost cover the entire land mass.
Glaciers begin forming because of snowfall accumulation. When snowfall exceeds the rate of melting in a certain area, glaciers begin to form. This melting occurs in the summer. The weight of snow accumulating compresses the snow to form ice. Because these glaciers are so heavy, they can slowly move their way down hills. Glaciers affect the topography of the land in some areas. Ancient glaciers formed lakes and valleys. The Great Lakes are an example of this. Glaciers range in length from less than the size of a football field to hundreds of miles long.
They also can reach up to 2 miles thick. Glaciers melting can have a tremendous effect on the sea level. If all of the glaciers were to melt today, the sea would rise an estimated feet, according to the USGS. Glaciers have had a tremendous effect on the formation of the Earth's surface and are still influencing the topography everyday.
Groundwater is defined as water that is found beneath the surface of the Earth in conditions of percent saturation if it is less than percent saturation, then the water is considered soil moisture. Ninety-eight percent of Earth's available fresh water is groundwater. It is about 60 times as plentiful as the fresh water found in lakes and streams.
Water in the ground travels through pores in soil and rock, and in fractures and weathered areas of bedrock. The amount of pore space present in rock and soil is known as porosity. The ability to travel through the rock or soil is known as permeability. A "high" permeability and porosity value means that the water can travel quickly. Groundwater can be found in aquifers.
An aquifer is a body of water-saturated sediment or rock in which water can move readily. There are two main types of aquifers: unconfined and confined. An unconfined aquifer is a partially or fully filled aquifer that is exposed to the surface of the land. Because this aquifer is in contact with the atmosphere, it is impacted by meteoric water and any kind of surface contamination.
There is not an impermeable layer to protect this aquifer. In contrast, a confined aquifer is an aquifer that has a confining layer that separates it from the land surface. This aquifer is filled with pressurized water due to the confining layer. If the water is pressurized at a high enough value, when a well is drilled into the confining aquifer, water rises above the surface of the ground.
This is known as a flowing water well. The pressure of the water is called the hydraulic head. Groundwater movement, or velocity, is measured in feet or meters per second..
In some areas, the bedrock has low permeability and porosity levels, yet groundwater can still travel in the aquifers. Groundwater can travel through fractures in the rock or through areas that are weathered. There is a lag, however, between when precipitation infiltrates the saturated zone and when the water table rises.
This is because it takes time for water to trickle through spaces between sediments to reach the saturated zone, although the process is helped by gravity.
Irrigation of crops can also cause the water table to rise as excess water seeps into the ground. During the summer months, the water table tends to fall, due in part to plants taking up water from the soil surface before it can reach the water table.
The water table level is also influenced by human extraction of groundwater using wells; groundwater is pumped out for drinking water and to irrigate farmland. The depth of the water table can be measured in existing wells to determine the effects of season, climate, or human impact on groundwater. The water table can actually be mapped across regions using measurements taken from wells. If water is not extracted through a well in a sustainable manner, the water table may drop permanently.
This is starting to be the case around the world. Some of the largest sources of groundwater are being depleted in India, China, and the United States to the point where they cannot be replenished.
Groundwater depletion occurs when the rate of groundwater extraction through wells is higher than the rate of replenish ment from precipitation. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited. Tyson Brown, National Geographic Society.
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