Ground water Flashcards
Groundwater
water below the Earth’s surface that fills voids in soils and rocks
Groundwater comprises __% of the water on earth
1%
Recharge
occurs when water enters into the subsurface and becomes groundwater by percolating into soil or rock at the surface
Groundwater recharge cycle
- Rainwater or snowmelt seeps into the ground
- Gravity moves water downward through the zone of aeration until it reaches the water table
- Flowpaths of water past water table lead to rivers
A spring will emerge where the water table intersects ____.
the surface
Zones of groundwater
Vadose (aeration, unsaturated), and saturated zone
Vadose and saturated zones are separated by the
water table
Vadose zone
the region nearer to the surface where pores or fractures in the subsurface are not entirely filled with water.
Posority
the amount of pore space in a geologic medium such as soil, sediment, or rock between 0 and 100%
Permeability
a measure of the ease with which a fluid can flow through a geologic medium.
Permeability is related to:
porosity and connectedness of pores
Clay permeability
Clay has high porosity but pores are small and poorly connected, so clay has low permeability
The water table is a subdued imitation of the ____.
landscape
the water table ____ under hills and ____ under valleys
rises
lowers
Relationship between the water table and the season
The water table will raise/lower depending on the seasons. During rain events and spring melt, the water table will rise.
What controls the exact position of the water table in the subsurface
the physical properties of the porous medium
Surface expressions of the water table
surface water bodies (rivers, lakes, and ponds)
What drives groundwater flow
gravity
Groundwater flows from regions of ___ pressure to regions of ___ pressure
from high pressure to low pressure
Hydraulic head
A measure of the pressure difference that drives groundwater flow.
Groundwater flow follows _____ paths.
curving
Groundwater flows from ___ areas to ____ areas.
recharge (infiltration) to discharge (rivers)
Discharge
A region where groundwater emerges at the surface
Examples of discharge areas
rivers, lakes, streams, wetlands
Springs
natural points of groundwater discharge that occur when the water table or permeability boundary intersects at the land surface
Aquifer
units of geological media that have sufficient capacity and high enough permeability to supply water at a rate useful to humans.
Two types of aquifers
Unconfined aquifer, confined aquifer
Unconfied aquifer
an aquifer in which the upper boundary is defined by the water table
Confined aquifer
an aquifer in which the upper boundary is defined by an aquiclude (geological media that stops the flow of media)
Aquiclude
units of geological media that have considerably slow flow or completely stop the flow of water (has low permeability) - usually have an impermeable rock layer on top
Cone of depression in the water table surrounding a well
occurs when the rate of groundwater withdrawal (pumping) exceeds the rate of local groundwater flow at a well
Groundwater causes the transportation of mass through the ___ and ___ of minerals in geologic media
dissolution and precipitation
Dissolution of minerals depends on
groundwater chemistry - groundwater pH
Precipitation of minerals occurs when
ions dissolve in groundwater come out of solution due to changes in factors such as pH, pressure, or evaporation
Stalactites
Rocks hanging from the ceiling
Stalagmites
rocks growing from the floor
How stalacites and stalagmites form
dissolved ions in groundwater precipitate to form rocks in caves due to evaporation and other changes in groundwater chemistry.
Cement
Mineral deposits in small pore spaces
Cement may convert loose sand into
sandstone
Cement may convert an aquifer into an
aquiclude
Cement may make a potential oil reservoir into a
non-porous non-reservoir
