groundwater. porosity & permeability porosity: - the percentage of the total volume of a rock...

Groundwater

Porosity & PermeabilityPorosity: - the percentage of the total volume of a rock consisting of voids. - pore spaces: spaces between mineral gains, fractures, solution cavities, vesicles

- for example:

vesicles & fractures in a basalt = 30-40% solution cavities in limestone = 30% spaces between grains in cemented sandstone = 5% spaces between grains in conglomerate = 20% fractures in granite = <1%

Permeability: - the capacity of a rock to transmit fluids - depends on the size of the voids, and whether the voids are interconnected. - a rock can have high porosity but low permeability if the voids are not connected so as to allow water to flow.- velocity of gw averages 1 m/day to 1 m/year.

Groundwater flows downhill and into areas of low pressure.Stream beds are areas of low pressure: Natural springs.

Water table drops belowlevel of stream bottom

Water table is at or abovelevel of stream bottom.

Spring

Groundwater Well: An artificial area of low pressure

Wells

Cone of Depression

Contaminated Wells

Vermillion

GW flowsN to S

Townwells

Wastewater treatment plant

Ogallala Formation:A trillion gallons of water putin the ground by melting glaciers10K years ago.

This water is used for irrigationin the midwest.

Center Pivot

128 Acres

Garden City, Kansas

Subsidence

Artesian Water

Pressurized groundwater rises from an aquifer

Blow Out

Water Tower

Water Reservoir

Table Rock Reservoir, South Carolina

New York Drought

52% decrease in capacityin two years

One reservoir in the CatskillMountains

Lake Mead

Wastewater Treatment

Karst Topography

Limestone Bedrock

Acidic groundwater slowly dissolves bedrock

Small Sink

Medium Sink

Large Sink

Stalactite

Water percolating throughthe ground leaves behindcalcite (CaCO3) deposits.

Stalactite

Stalagmite

Column

Geysers & Hot Springs

Geyser Formation

Groundwater percolates downward;as it approaches magma at depth, itheats up. When it flashes into steam,the steam rushes back up to thesurface forming a geyser. Then theprocess repeats.

Sometime this process repeats at aregular interval, sometimes not.

Old Faithful

Colorado River Delta

River endshere

Only 10%of river watermakes it into Mexico

Aral Sea Reduced in sizeby 60% in 30 years

Commercial fishingeliminated

Lake Chad

Lake Chad

1/20th of itssize 20 yrs ago!