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