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