GROUNDWATERGROUNDWATER
Minerva Terrace, Yellowstone WYMinerva Terrace, Yellowstone WYMinerva Terrace, Yellowstone WYMinerva Terrace, Yellowstone WY
underground water stored in the pore spaces of rock, sediment, or soil
important resource for domestic, industrial, and agricultural use
important erosional agent
important energy source in some areas
underground water stored in the pore spaces of rock, sediment, or soil
important resource for domestic, industrial, and agricultural use
important erosional agent
important energy source in some areas
HYDROSPHEREHYDROSPHERE Oceans 97.2%
Glaciers 2.15%
GROUNDWATER 0.62%
Other 0.03%
lakes 0.009%
inland seas 0.008%
soil 0.005%
atmosphere 0.001%
streams 0.0001%
biosphere 0.0069%
Oceans 97.2%
Glaciers 2.15%
GROUNDWATER 0.62%
Other 0.03%
lakes 0.009%
inland seas 0.008%
soil 0.005%
atmosphere 0.001%
streams 0.0001%
biosphere 0.0069%
POROSITY and PERMEABILITYPOROSITY and PERMEABILITY
Porositythe percentage of a
material’s volume that is pore space
Permeabilitya measure of the
interconnectedness of pore spaces
Porositythe percentage of a
material’s volume that is pore space
Permeabilitya measure of the
interconnectedness of pore spaces
well sorted = high porosity poorly sorted = low porosity
carbonates, evaporites metamorphic or igneous rocks
POROSITYPOROSITYUnconsolidated sediment
soil 55%
gravel 20-40%
sand 25-50%
silt 35-50%
clay 50-70%
Rockssandstone 5-30%
shale 0-10%
carbonates, dissolution 10-30%
basalt, fractured 5-40%
granite, fractured 10%
Unconsolidated sedimentsoil 55%
gravel 20-40%
sand 25-50%
silt 35-50%
clay 50-70%
Rockssandstone 5-30%
shale 0-10%
carbonates, dissolution 10-30%
basalt, fractured 5-40%
granite, fractured 10%
POROSITY & PERMEABILITY
POROSITY & PERMEABILITY
Porositysand 25-50%
clay 50-70%
PermeabilitySand: high permeability
Clay: low permeability
“Aqui-” Terms“Aqui-” Terms
Zone of aerationpore spaces contain mostly air
Zone of saturationpore spaces contain mostly water
Water tablethe top of the zone of saturation
Capillary fringesurface tension pulls water up from the saturated zonefew cm’s to several meters thick
“Aqui-” Terms“Aqui-” Terms
Aquifer: a permeable layer that transports groundwater
Confined (closed)Unconfined (open)
Aquiclude or Aquitard: an impermeable layer that prevents or retards the movement of groundwater
Variations in the Water TableVariations in the Water Table
Shape of the water table mimics the shape of the landscape
Wherever the water table intersects the Earth’s surface, there is free-flowing or free-standing water (springs, ponds)
Water-level in wells = position of the water table
Variations in the Water TableVariations in the Water Table
Groundwater FlowGroundwater FlowGravity moves groundwater,
just as it does water in channels•moves from areas of high
pressure to areas of low pressure
•may move up to 250 m per day, or less than a few cm/day
Groundwater “piles up” beneath high areas because it moves so slowly; if rainfall stopped, the “hills” in the water table would slowly flatten out.
Groundwater Flow
Groundwater Flow
Mapping the water table. The water level in wells coincides with the water table.
A. The locations of wells and the elevation of the water table above sea level are plotted on a map.
B. These data points are used to guide the drawing of water table contour lines at regular intervals (10 ft). Flow lines (dashed) are added to show water movement in the zone of saturation.
Gaining Steams/Losing StreamsGaining Steams/Losing StreamsGaining streams receive water from the GW system: water table above stream.
Losing streams lose water to the GW: water table below stream.
When losing streams are separated from the GW system by the zone of aeration, a bulge may form in the water table: rate of infiltration > rate of GW flow
Movement of GWMovement of GWSlope of the water table = hydraulic gradient
h1 - h2
d
Steeper slope = faster flowGreater permeability = faster flow(hydraulic conductivity K)
Darcy’s Law (aquifer discharge)Q = K•A(h1 - h2)
d
SpringsSpringsPlaces where groundwater flows or
seeps out of the groundwhen percolating water reaches the
water table or an impermeable layer, it flows laterally and may intersect the surface, yielding a spring
Marble Canyon AZ
Artesian AquifersArtesian Aquifers
“artesian”
GW under pressure rises above the level of the aquifer
Non-flowing
Free-flowing
Artesian AquifersArtesian Aquifers
Oasisdesert spring
Oasisdesert spring
WELLSpenetrate the zone of saturation
WELLSpenetrate the zone of saturation
Water level in the well marks the position of the water table.
Pumping water from wells causes drawdown of the water table around the well, creating a cone of depression
WELLSpenetrate the zone of saturation
WELLSpenetrate the zone of saturation
Hot Springs and GeysersHot Springs and Geysers
GW is heated as it circulates at depth or near cooling magma bodies travertine, tufa
sinter, geyserite
Hot Springs and GeysersHot Springs and Geysers
DepletionDepletion
Lowering of the water table (depletion) occurs when GW is pumped out faster than it is replenished (non-renewable resource).
Largest aquifer in the U.S. = Ogallala Aquifer (High Plains Aquifer)
SubsidenceSubsidence Subsidence of the ground surface occurs when GW is pumped out faster than it is replenished in some areas (compaction).
San Joaquin ValleyNew Orleans, LAMexico City
Saltwater Contamination
Saltwater Contamination
Saltwater contamination occurs in coastal areas when GW is pumped out faster than it is replenished.
Recharge wells and drainage basins help to replenish fresh GW.
Orange County CALong Island NY
PollutionPollution Hazardous pollutants = flammable, corrosive, explosive, toxic
Pollution sources:Sewer systems and septic tanksFarm wastes and fertilizersIndustrial chemicals from pipes, tanks, or holding pondsLandfills
A. Although the contaminated water has traveled more than 100 m before reaching Well 1, the water moves too rapidly through the limestone to be purified.
B. As the discharge from the septic tank percolates through the sandstone, it is purified in a relatively short distance.
PollutionPollution
A. Originally the outflow from the septic tank moved away from the small well.
B. The heavily pumped well changed the slope of the water table, causing contaminated GW to flow toward the small well.
GW ErosionGW Erosion
Depositional features (speleothems) form as water percolates through the unsaturated zone:
stalactites, stalagmitessoda straws, columns
Caverns form as a result of dissolution of carbonate rocks below the water table
GW ErosionGW Erosion
Carlsbad Caverns NM
KARSTKARSTKarst Topography
A. GW percolates through limestone along joints and bedding planes. Dissolution creates and enlarges caverns at and below the water table.
B. Sinkholes form when the roof of a cavern collapses. Surface streams may disappear down sinkholes and reappear as springs.
C. As time passes, caverns grow larger and the number and size of sinkholes increase. Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions (solution valleys). Eventually dissolution may remove most of the limestone from the area, leaving only isolated remnants (towers).
KARSTKARSTGuilin CHINA