Questions and Answers
Where can groundwater be found?
Underground in the pore spaces between grains in sediments and rocks or in fractures and cavities in rocks.
What is the hydrologic cycle?
The circulation of water from the Earth's surface to its atmosphere and back again.
What does the Earth's water budget equation state?
Precipitation = Runoff (Streams) + Evapo-transpiration (Clouds) + Infiltration (Groundwater)
Which factors control the balance between runoff and infiltration? (Select all that apply)
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What is porosity in relation to groundwater?
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What is hydraulic conductivity?
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What are the two zones found in the groundwater system?
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What is the water table?
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What affects the velocity of groundwater in porous materials?
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What is an aquifer?
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What is an aquiclude?
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Study Notes
Groundwater Overview
- Groundwater is located underground in pore spaces of sediments and rocks, or within fractures and cavities in rocks.
- Constitutes approximately 51% of drinking water for the entire U.S. population and 99% for the rural population.
- Represents a small portion of the Earth's hydrosphere.
Hydrologic Cycle
- Describes the continuous circulation of water from the Earth's surface to the atmosphere and back.
- Involves processes: evaporation, transpiration, precipitation, infiltration, and runoff.
- Solar energy drives the cycle, facilitating water vapor's journey through these processes.
Earth's Water Budget
- Balance of water can be expressed as:
- Precipitation = Runoff + Evapo-transpiration + Infiltration.
Factors Influencing Runoff vs. Infiltration
- Intensity and duration of rainfall affect runoff; lower intensity favors infiltration.
- Soil texture governs porosity and permeability, influencing infiltration rates.
- Topography: flat and gently sloping surfaces enhance infiltration.
- Land use changes: vegetation (grass, forest) promotes infiltration; bare or urban land increases runoff.
- Climate conditions: arid climates favor runoff due to higher evaporation rates and less vegetation.
Storage and Movement of Groundwater
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Porosity is the percentage of void space in sediment or rock, indicating groundwater storage capacity.
- Primary porosity develops when rock forms.
- Secondary porosity results from fractures and cavities formed after rock formation.
Permeability
- Defined as the capacity of materials to transmit fluids, relevant for groundwater movement.
- Expressed in rates, e.g., inches/day or centimeters/day.
Structure of Water Table
- Comprises three zones: Unsaturated Zone, Saturated Zone, and the Water Table.
Unsaturated Zone
- Located just below the land surface, where pores contain both water and air.
- Water in this zone is referred to as soil moisture, not groundwater.
Saturated Zone
- Area beneath the surface where all pores are filled with water.
Water Table
- The upper surface of the saturated zone, fluctuates with water recharge and discharge.
Factors Affecting Groundwater Velocity
- Velocity depends on hydraulic conductivity (measure of permeability) and hydraulic gradient (slope of the water table).
- Darcy's Law illustrates the relationship:
- V = K (h/L)/n, where V is velocity, K is hydraulic conductivity, n is porosity, h is head difference, and L is horizontal distance.
Aquifer
- Composed of porous and permeable materials, capable of storing and transmitting water.
- Varies greatly in size and thickness, ranging from small areas to extensive regions below the surface.
Aquiclude
- A formation that restricts water movement, typically made up of less permeable materials compared to an aquifer.
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Test your knowledge on groundwater concepts with these flashcards. Explore the definition, significance, and location of groundwater within the hydrologic cycle. Perfect for students and enthusiasts of earth sciences.
