Hydrology

Hydrology

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Hydrologic Cycle
Groundwater Terminology

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University

Hydrologic Cycle

	Total Water	Fresh Water	Unfrozen Water (Fresh)
Ocean	97 %	-	-
Ice	2 %	87 %	-
Ground	0.6 %	13 %	97 %
Lakes and Streams	-	0.3 %	3 %
- Fresh Water	0.009 %	-	-
- Salty Water	0.008	-	-

Groundwater Terminology

Zone of Saturation
The area where all the pore space in the ground is filled with water.

Zone of Aeration

The area of where the pore space is mostly empty, or full of air.

Water Table

The level below which the ground is saturated.

Groundwater Aquifer

A large volume of the subsurface that is thoroughly saturated with water, and through which water travels freely. It contains a large volume of water which can be accessed for use.

Aquiclude

A layer of impermeable material, for example clay, that prevents water from passing through.

Perched water table

Subsurface area saturated with water above an aquiclude, forming a local water table above the regional  water table..

Hydraulic Conductivity

A measure of permeability. ( How fast does the water travel through the substance?).

Hydraulic Gradient

The difference in the elevation of the water table over a given length.

The rate of groundwater flow is dependent on the hydraulic conductivity and hydraulic gradient.

The greater the conductivity or the greater the gradient the more rapid groundwater flows.

Transpiration

The process by which water sorbed by plants is returned to the atmosphere as a gas.

Evapotranspiration

The combined processes of Evaporation and Transpiration.

Porosity

The percentage of void space in a rock.

• Well sorted sand may have a porosity of 30% to 40%.
• Poorly sorted sand will have a lower porosity because the finer grained sediment fills the spaces between the larger grains.
• Most igneous rocks have very low to no porosity.
• Limestones may have a low or high porosity. If it has undergone erosion or dissolution, it may even have large caverns.

Permeability

The ease with which water can pass through a substance.

A substance through which water cannot pass is said to be Impermeable.

The permiability of various sediment types, ranging from most permeable to least permeable, is:

Gravel Most permeable

Sand

Silt

Till

Clay Least permeable

Hydraulic Head
The term applied to water pressure due to the difference in the height of water in a closed system. Water tends to reach its own level. This phenomena may result in artesian wells and springs, and is used in providing water to  municipalities via a water tower.

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