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30 Cards in this Set
- Front
- Back
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Groundwater
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1. Precipitation
2. Water soaks into the ground 3. Water sinks deeper and fills cracks between grains 4. Water flows slowly, downhill underground 5. Water is exposed as lakes at regions of low topography |
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Why groundwater is important
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Groundwater represents largest reservoir available to us
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Porosity
Permeability |
• Porosity- amount of open space within a material, holes between the breaks
• Permeability- measure of ease with which fluids can flow through a material • Depends on: - Number of conduits (cracks or spaces between grains - Size of conduits - Straightness of conduits |
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Types of materials that you would expect to be highly permeable:
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• High permeability = granite with many fractures and loosely cemented gravels
• Low permeability = compacted clay (shale) and porous volcanic rock with separate pores |
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-Aquifer
-Aquitard |
• Aquifer- water flows
• Aquitard- water can’t flow |
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Why groundwater follows a curved path:
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The flow mimics the topography.
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The definition of hydraulic head and hydraulic gradient:
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Hydraulic Head – potential energy available for groundwater flow
• Higher elevation, higher pressure = higher hydraulic head • Goes from high elevation/ high pressure to low elevation/ low pressure • Flow due to a combination of gravity and differences in pressure Hydraulic gradient - the change in hydraulic head per unit of distance |
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The difference between the two types of wells:
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Ordinary well - Drilling a hole into an unconfined aquifer (open to the atmosphere), needs to be pumped or brought up
Artisan well - drilling a hole into a confined aquifer, well flows naturally, region of pressure so water will naturally flow up |
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Springs
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place where groundwater naturally flows onto the surface, towns have been built around springs
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Hot Springs
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springs heated by some sort of magma underneath the ground
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Geysers
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Water reaches boiling point and explodes and then shortly after refills and process happens again
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Oasis
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vast desert where natural springs fill up at the surface
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How climate and season affects the water table:
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During wet seasons, water table is high and during dry seasons, water table is low
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How humans can affect the water table:
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• City removes water from the aquifer, lowering the water table → nearby lakes and rivers can dry-up
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The negative consequences associated with lowering the water table:
-Water diverted from recharge zone -Direction Reversal -Saline Intrusions -Land Subsidence |
• What happens if water is diverted from the recharge zone? Water table lowers, swamps dry, saltwater intrudes
• Direction Reversal - Large well draws the water table down, reversing the flow → contamination that would have flowed away is now directed into the well, so becomes polluted • Saline Intrusions - With pumping from a well, boundary between salty water and fresh water rises → saltwater enters the well • Land Subsidence – when water is removed, volume of sediment decreases → land packs together and cracks form -Irreversible |
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Rising water tables
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- can cause landslides and slumping
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Cone of depression
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when the water table becomes a downward-pointing, cone-shaped surface
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Contaminant plume
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the cloud of contaminated groundwater that moves away from the source of contamination
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Darcy’s law
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Groundwater flows faster through more permeable material and along steeper slopes
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Disappearing streams
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where surface streams intersect cracks or holes that link to the caves below, the water disappears into the subsurface and becomes an underground stream
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Discharge area
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the location where groundwater flows back up to the surface
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Geyser
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– a fountain of steam and hot water that erupts episodically from a vent in the ground
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Groundwater
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subsurface water in the saturated zone, where water completely fills pores
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Groundwater contamination
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the addition of substances that make the groundwater dangerous to use
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Hydraulic gradient
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the change in hydraulic head per unit of distance between two locations as measured along the flow path
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Pore
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any open space within a volume of regolith, or within a body of rock
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Recharge area
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the location where groundwater enters the ground (i.e. where the flow direction has a downward trajectory)
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Saturated zone
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deeper down, water completely fills, or saturates, the pores
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Unsaturated zone
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the region of the subsurface in which water only partially fills pores
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Water table
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the horizon that separates the under saturated zone above the saturated zone below
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