chapter 14-1 groundwater pages 298-315 geology. groundwater factors that affect the amount of...
TRANSCRIPT
Groundwater
Factors that affect the amount of seepage of water into the ground are:
1.Type of rock or soil on the ground where the water falls
2.Climate, topography, land use, vegetation
Porosity
• The percent of a materials volume that is pore space – the more the space, the more water that can be held.
• Depends on: – Particle shape
• More rounded particles allows for more pore spaces
– Sorting• Well sorted material (same size) offers greatest pore
spaces
Permeability• The rate at which water or other liquids pass
through the pore spaces of a rock.– Permeability increases with grain size– Ex: sand and gravel is highly permeable while
clay and shale has low permeability.
– So, can a rock be highly porous but not be permeable? – explain…
– Or, can a nonporous rock become highly permeable?
The water table
• The water table is the upper surface of the zone of saturation
• Above this level up to the surface, the ground can still hold more water, and this area is called the zone of aeration– This zone of aeration contains 3
parts:
• The three parts of the zone of aeration are:– 1) capillary fringe
• Found just above the water table, where water rises due to water’s attraction to the soil particles.
• This is called Capillary action– 2) a dry region of soil except after rainfall– 3) organic or humus layer just below the
surface
How is the water table important?
• Seepage from water table keeps streams flowing between rain events
• Maintains water levels of lakes and wetlands
• Provides drinking water from natural springs and human-made wells
Types of wells• Ordinary well
– Water must be pumped out of the well• Artesian well
– Well water is under some pressure to force the water up the well – does not have to be to the top.
Large volumes of water found underground in the pore spaces is called an aquifer.
***best aquifers are those made of uncemented sands and gravel, followed by porous sandstones.
How does a geyser occur?
• Geyser animation
Water budget• Describes the income and spending of water
for a region.– The income is rain or snow– The spending includes water loss by use, runoff,
and by evapotranspiration.• Weather is the controlling factor of evapotranspiration
- when temperatures are high, the amount of evapotranspiration would also increase.
- the opposite is also true, low temperature causes low evapotranspiration.
Four parts of a water budget
• Recharge– When moisture is added to the groundwater, the soil
water storage is filling• Surplus
– Occurs when the rainfall is greater than the need for moisture, and the storage water is filled
• Usage– If the need for moisture is greater than the rainfall and
the plants draw water from the soil water supply• Deficit
– Occurs when the need for moisture is greater than the rainfall and the soil water is gone.
Water conservation
• In many regions, water is being used at a faster rate than can be naturally replenished.
Pollution is also threatening many groundwater supplies
Overuse of groundwater
• When groundwater supplies are depleted, the water table drops– This may cause wells, springs to go dry
– If this happens along coastal regions, salt water may seep into overused freshwater aquifers and damage water supplies by making them salty and unusable.
• Overuse of groundwater may cause ground levels to drop due to compaction of the removal of groundwater below.
– Entire valleys may subside like the San Joaquin Valley of California (up to 30 feet drop from 1925-1977)!
Sinkholes may formfrom loss of groundwater
• In Bowling Green, KY
• In Florida
Groundwater pollution• Groundwater may become polluted by
human activities:
– Fertilizer
– Oil from roadways
– Pesticides
– Sewage from septic tanks and sewers
– Hazardous wastes from industry
– Toxic waste dumps (Love Canal – New York)
Geologic formations formed by groundwater
• Groundwater moving through bedrock may take in dissolved minerals.
• This water is now called “hard water”.Calcium ions is most common mineral in hard H2O
• What do we do at home to reduce hard water?
• Hard water causes water spots, poor washing• Artesian water is usually harder than regular
groundwater• Groundwater is almost always harder than river water
Mineral deposits
• When water evaporates or cools, it will leave behind any minerals that were dissolved in the water.– Examples: geyserite, geodes, mineral veins of
copper, quartz, gold, silver, calcite, etc.
• Petrified wood is formed when minerals replace decaying wood of buried trees
• Calcite is most common dissolved mineral cement for grains of sand and pebbles.
Mineral springs• A spring with a high concentration of mineral
matter– May be due to:
• Hot water• Water passes through easily dissolved
minerals• Water contains large quantity of gases
• Some mineral springs areas have become health resorts – Hot Springs, Arkansas
• Yellowstone’s Mammoth Hot Springs forms calcium deposits called traventine
Caverns
• Formed in areas with limestone bedrock• Limestone is dissolved by carbonic acid found in
the groundwater– Dripstone – Stalactites– Stalagmites
• When they meet, they form columns or pillars
• Examples include Mammoth Cave in Kentucky, caves of Calumet and Door County, WI, Eagle Cave west of Madison
Karst Topography
• Identified by sinkholes, sinkhole ponds, fissures, lost rivers, and underground rivers
• Created when caverns collapse
• Forms where bedrock is made of calcite or dolomite
• Found in south-central Kentucky, Door County, WI