Hydrogeology

Hydrogeology is the study of how Earth's hydrosphere interacts with its geosphere. It deals with the processes involved in groundwater, including its distribution and movement.

Event Overview
This event consists of three parts; a written test (25% of the total score in the event), the use of a model to answer questions (25% of the total score), and the use of a scenario to evaluate and assess the risk of the contamination of a well along with the application of knowledge to create possible solutions for the reduction of anthropogenic effects on groundwater (50% of the total score).

Students are permitted to bring one double-sided 8.5" by 11" note sheet.

Hydrologic Cycle
For more information on the hydrologic cycle, visit the Hydrologic Cycle page.

Aquifers
Aquifers are underground geological structures that can store and release water. Confined aquifers are aquifers that are confined between two impermeable layers (layers that do not allow water to pass through). Unconfined aquifers are aquifers which allow water to seep/flow freely through them. There are also aquitards, which can collect water but not release it; and aquicludes, which do not collect or release groundwater.

Darcy's Law
Darcy's law is a fundamental law in hydrogeology, made by Henry Darcy in 1858. It is an equation that relates the properties of an aquifer to the velocity that water flows through it. The law comes in many forms, but the most simple is $$V=ki$$, where V is the apparent velocity, k is the permeability of the aquifer (how well water can flow through it), and i is the hydraulic gradient of the aquifer. Permeability is a property of rocks and soils, of the speed at which water flows through it with no relation to gravity. The hydraulic gradient is basically the slope of the aquifer; the rate at which the aquifer moves downward (this accounts for gravity). However, this version of Darcy's law does not account for "turns" in the rock/soil of the aquifer. A more commonly seen version of Darcy's law is $$V=ki/n$$, where n is equal to the porosity of the rock, as a percentage; and V is equal to true velocity.

Different Zones of Aquifers
Aquifers are split into different areas, or zones.
 * The first zone division is between the zone of aeration and the zone of saturation (also known as the phreatic zone), separated by the water table. The zone of saturation is below the water table, and is saturated, or contains groundwater. The zone of aeration is above the water table, and contains very little water.
 * The zone of aeration (also known as vadose zone) is split into the soil water zone, the intermediate vadose zone, and the capillary fringe. The soil water zone goes from the ground surface, down to the depth of the deepest plant roots. This is because plants soak up groundwater through transpiration, and thus makes it more difficult for water to infiltrate to lower zones. The next lowest is the intermediate vadose zone, in which there can be some water held by adhesive properties of water and the vadose zone's material composition. The capillary fringe is closest to the aquifer, in which water is held by capillary action (a property of liquids that lets them travel against gravity through small spaces), as well as adhesion. The depths of these zones fluctuate over time, depending on seasons, long term change, daily environmental changes, etc.

Similar Events

 * Awesome Aquifers
 * Earth's Fresh Water

Links
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