Geology 4 Essay

Groundwater

The most abundant supply of readilyavailable fresh water Some photos in this presentation may be copyrighted. Well, shiver me timbers! We gets to study groundwater! Groundwater is the largest reservoir (94%) of fresh water readily available to humans. It is used for:

Pivot point

Wheels driven by motors

These circular fields are irrigated by center pivot irrigation systems as shown in the inset above.

GROUNDWATER: Our largest source of readily available fresh water.

The #1 use of groundwater Water Table Formation

This animation shows that groundwater results from infiltration, and the water table (upper surface of groundwater) is typically a subdued replica of the land. Additionally, while rain and snow melt recharge the groundwater, most groundwater is discharged by flowing into streams.

In a humid region water (from precipitation) infiltrates into Earth until it hits a “confining unit”.
Above the confining unit the rock/sediment becomes saturated up to a given height. The upper limit of saturation is called the water table. The water table may fluctuate with dry and wet seasons but is generally a subdued replica of the topography above.

The water table separates the zone of saturation from the zone of aeration. It is usually a subdued replica of the surface topography.

In an unconfined aquifer the water table elevation may fluctuate with different seasons. Note that groundwater is pretty much ubiquitous (present everywhere). Most groundwater is not in an underground stream!

Water Dowsing (Witching)
What makes Bob so different? He is a Water Witcher and has the gift of finding underground water with nothing more than a wooden branch in his hands.
He shows you how it works. When his body crosses an underground stream, the branch that he holds firmly in his two hands will dip down toward his feet. Even after you watch Bob criss cross your property, stick pointing straight out in front of him, then dipping downward, you remain skeptical. But then it dips again and soon a pattern develops. He can close his eyes, talk or whistle. He does not have to concentrate on what he is doing. No matter how hard he tries to stop it, the forked willow seems to have a mind of it's own.
Experienced ground-water geologists try to discredit this practice, calling it unscientific and
"fallacious reasoning." Regardless of their opinions, many people still phone a Water
Witcher (or Dowser) first, to hopefully save some money. (How about waste some money?)

Test drilling for water can add up to thousands of dollars in a hurry. Last year Bob visited over 50 sites for people that believed in his talent. He doesn't know how to explain the phenomenon himself, saying its possibly an electromagnetic force within his body. Yes, I asked... his watch works fine. But other things do get a little strange.

Groundwater flows under the force of gravity from areas of high elevation to areas of low elevation. Flow rates are highly variable, but commonly on the order of a few inches a day.
The hydraulic gradient is the slope of the water table over a given distance.

Flow rates depend on the hydraulic gradient and the permeability
(the ability to let fluids flow ) of the material.

Groundwater flows into a gaining stream, whereas a losing stream loses water to groundwater. Many streams gain in some sections and lose in others. Overall, most streams are gaining streams.

Porosity is storage capacity. The ‘blue’ in this diagram to the left is water filling the pore space around grains of sand.
Aquifers are both porous and permeable zones within Earth containing groundwater.
Aquitards may have good storage capacity (porosity), but are impermeable, retarding the flow of water.
•Larger grain sizes allow for greater porosity and permeability
•Spherical shapes allow for greater porosity and permeability

Factors that favor good porosity and permeability include:

•Well-sorted materials (all particles are about the same size) allows for

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