How is groundwater flow primarily controlled

Actually, it is pretty much a myth. Even though there are some caverns, lava and ice tubes, and horizontal springs that can carry water, the vast majority of underground water occupies the spaces between rocks and subsurface material. Generally, water underground is more like water in a sponge. It occupies the spaces between soil and rock particles. At a certain depth below the land surface, the spaces between the soil and rock particles can be totally filled with water, resulting in an aquifer from which groundwater can be pumped and used by people.

Some of the precipitation that falls onto the land infiltrates into the ground to become groundwater. If the water meets the water table below which the soil is saturated , it can move both vertically and horizontally. Water moving downward can also meet more dense and water-resistant non-porous rock and soil, which causes it to flow in a more horizontal fashion, generally towards streams, the ocean , or deeper into the ground.

If groundwater wants to be a member in good standing of the water cycle, then it can't be totally static and stay where it is. As the diagram shows, the direction and speed of groundwater movement is determined by the various characteristics of aquifers and confining layers of subsurface rocks which water has a difficult time penetrating in the ground. Water moving below ground depends on the permeability how easy or difficult it is for water to move and on the porosity the amount of open space in the material of the subsurface rock.

If the rock has characteristics that allow water to move relatively freely through it, then groundwater can move significant distances in a number of days. But groundwater can also sink into deep aquifers where it takes thousands of years to move back into the environment, or even go into deep groundwater storage , where it might stay for much longer periods.

If an aquifer is under enough pressure, an artesian well tapping the aquifer can result in pressurized water shooting above the land surface. Bottled water is a very popular beverage nowadays all over the world. Sometimes it is because the local drinking water is of lower quality and sometimes it is just a convenience. Some bottled water is advertised as "artesian well water".

Is the water really any different than other groundwater? Artesian well water is not really different from non-artesian well water - but it comes to the surface in a different manner. In the diagram above, you can see that there are unconfined and confined aquifers in the ground. The confinement of water in an aquifer, which can result in pressure, determines if water coming from it is artesian or not. Wells drilled into confined aquifers can yield artesian water. So, in what way is bottled artesian well water different from other well water?

Mainly, the company that bottles it doesn't have to go to the expense of installing a pump in their well.

As these charts show, even though the amount of water locked up in groundwater is a small percentage of all of Earth's water , it represents a large percentage of total freshwater on Earth. The pie chart shows that about 1. As the bar chart shows, about 5,, cubic miles mi 3 , or 23,, cubic kilometers km 3 , of groundwater exist on Earth. About 54 percent is saline, with the remaining 2,, mi 3 10,, km 3 , about 46 percent, being freshwater. Source: Gleick, P.

In Encyclopedia of Climate and Weather, ed. Do you think you know about groundwater? Quiz icon made by mynamepong from www. Earth's water is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Water is always changing states between liquid, vapor, and ice, with these processes happening in the blink of an eye and over millions of years. The air is full of water, even if you can't see it.

Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail What is streamflow?

How do streams get their water? To learn about streamflow and its role in the water cycle, continue reading. Perhaps you've never seen snow. Or, perhaps you built a snowman this very afternoon and perhaps you saw your snowman begin to melt. Regardless of your experience with snow and associated snowmelt, runoff from snowmelt is a major component of the global movement of water, possibly even if you live where it never snows.

For the water cycle to work, water has to get from the Earth's surface back up into the skies so it can rain back down and ruin your parade or water your crops or yard. It is the invisible process of evaporation that changes liquid and frozen water into water-vapor gas, which then floats up into the skies to become clouds. The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor which rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.

The air is full of water, as water vapor, even if you can't see it. Condensation is the process of water vapor turning back into liquid water, with the best example being those big, fluffy clouds floating over your head. And when the water droplets in clouds combine, they become heavy enough to form raindrops to rain down onto your head. You can't see it, but a large portion of the world's freshwater lies underground.

It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts. Water in the ground keeps all plant life alive and serves peoples' needs, too.

Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human Recall that water is flowing in pores where there is friction, which means it takes work to move the water. There is also some friction between water molecules themselves, which is determined by the viscosity. Water has a low viscosity, but friction is still a factor.

All flowing fluids are always losing energy to friction with their surroundings. Water will flow from areas with high energy to those with low energy. Recharge areas are at higher elevations, where the water has high gravitational energy. It was energy from the sun that evaporated the water into the atmosphere and lifted it up to the recharge area. The water loses this gravitational energy as it flows from the recharge area to the discharge area. In Figure The water table is higher under the recharge area 90 m and lower at the discharge area 82 m.

Imagine how much work it would be to lift water 8 m high in the air. That is the energy that was lost to friction as the groundwater flowed from the top of the hill to the stream.

The situation gets a lot more complicated in the case of confined aquifers, but they are important sources of water so we need to understand how they work. As shown in Figure The red dashed line in Figure If we drill a well into the unconfined aquifer, the water will rise to the level of the water table well A in Figure But if we drill a well through both the unconfined aquifer and the confining layer and into the confined aquifer, the water will rise above the top of the confined aquifer to the level of its potentiometric surface well B in Figure This is known as an artesian well , because the water rises above the top of the aquifer.

In some situations, the potentiometric surface may be above the ground level. This is known as a flowing artesian well. In situations where there is an aquitard of limited extent, it is possible for a perched aquifer to exist as shown in Figure Although perched aquifers may be good water sources at some times of the year, they tend to be relatively thin and small, and so can easily be depleted with over-pumping.

In , French engineer Henri Darcy carried out some experiments from which he derived a method for estimating the rate of groundwater flow based on the hydraulic gradient and the permeability of an aquifer, expressed using K , the hydraulic conductivity.

We can apply this equation to the scenario in Figure If we assume that the permeability is 0. That is equivalent to 0. That means it would take 1, days nearly four years for water to travel the m from the vicinity of the well to the stream. Groundwater moves slowly, and that is a reasonable amount of time for water to move that distance. She calls in a hydrogeologist to find out how long it might take for the fuel contamination to reach the nearest stream.

The sandy sediment in this area has a permeability of 0.