Geology: Chapter 14 - Ground Water
Freshwater
-75% comes from surface sources -25 % comes from ground water
Irregular Surface
-A property of the water table -groundwater moves very slowly at varying rates under different conditions -variations in precipitation, difference in surface permeability -water will pile up beneath high areas between stream valleys -if a drought occurs the water tables will drop
Zone of Saturation
-Phreatic Zone -water that isn't held in soil moisture moves down until it reaches this zone -this zone is where all the open spaces in sediment and rock are completely filled with water -also called the phreatic zone -the water here in this zone is called groundwater -wells can pump water from here because the water pressure is
Water Table
-The upper limit of the zone of saturation -important in predicting the productivity of wells -helps explain changes in flows and springs -fluctuates levels of lakes -can range from right under the surface to hundreds of meters down -rarely level
Artesian Systems
-act like conduits -often transmitting water great distances from remote areas of recharge to points of discharge
Hydrosphere
-all of earths water -only about 6/10ths of 1% is ground water
Discharge Areas
-along streams where ground water is flowing back to the surface -also occurs at springs, lakes or wetlands as the groundwater seeps into bays or oceans -also when plant have roots near the water table -and when wells pump the water up to the surface -describe the movement of groundwater from the subsurface to the surface
Artesian
-applied to any situation in which groundwater under pressure rises above the level of the aquifer
Recharge Areas
-areas where groundwater is being replenished
Water
-basic to life -called the blood stream of both biosphere and society -each day in the US we use about 306 billion gallons
Sinkholes formed Abruptly
-can come very fast when the roof of an underground cavern collapses under its own weight -usually the depressions are steep sides and deep
Limestone
-covers a lot of the earths surface -very suseptible to being dissolved by water that has small quantities of carbonic acid -most groundwater contains this acid therfore eroding this rock away and creating sink holes and caverns
Dripstones
-depositional features created by dripping of water over spans of time -dont occur until the cavern is above the water table in the unsaturated zone -as soon as the cave is filled with air then these start to form
Sinkholes
-depression in the ground -contain a lot in florida -they can form overtime or very abruptly -some get plugged with clay or debris causing small lakes or ponds to form
Darcy's Law (Discharge Formula)
-discharge is the actual volume of water that flows through through an aquifer at a given time Q= KA(h1-h2) ---------- d k= hydraulic conductivity a=cross sectional area of aquifer
Stalagmites
-form on the floor of the cave and reach upward toward the ceiling -the water supplying the calcite and providing the growth falls from the ceiling and splatters on the surface -dont have a straw shape, usually just more round and big
Perched Water Table
-forms where an aquitard is situated right above the main water table -for example massive igneous and metamorphic rocks
Freshwater
-glaciers compose of most of freshwater at 70% -but ground water still counts as about 30%
Hydraulic Conductivity
-groundwater flows more rapidily through sediments having greater permeability than through materials of lower permeability
Environmental Problems
-groundwater is being exploited at an increasing rate -overuse threatens the groundwater supply -groundwater withdrawl has caused the ground and everything around it to sink
Geothermal Energy
-harnessd by tapping natural underground reservoirs of steam and hot water -the steam and hot water are used for space heating and to generate electricity -biggest geothermal installation formed in 1960 at the Geysers north of san fran
Clay
-has lots of pores to store water -but the pores are so small it doesnt allow the water to move through it -its an aquitard
Geysers
-hot springs or fountains in which columns of water are ejected with great force at various intervals -after water comes out steam follows
Aquitards
-impermeable layers that hinder or prevent water movement are termed -ex. clay
Caverns
-in the US there are about 17000 -form from when groundwater erodes limestone creating caves -most created at or just below the water table in the zone of saturation -material that is dissolved is discharged into streams and then taken to the ocean -as the elevation drops the water table drops -the caves become abandoned as the water table drops further
Unsaturated Zone
-includes the capillary fringe and zone of soil moisture -also called the vadose zone -the pore spaces in this zone contain both air and water -there can be a good amount of water here but it cant be pumped because the water clings to tightly to the rock and soil particles
Zone of Soil and Moisture
-its crisscrossed by roots, voids left by decayed roots and animal and worm burrows -enhances the infiltration of rain water into soil -some water that soaks into the ground doesnt travel far because it held near the surface -used by plant and animals in life functions -sometimes the water is evaporated back into atmosphere
Sinkholes formed over time
-limestone below the soil is dissolved by downward seeping of rainwater containing carbonic acid -with time the bedrock surface is lowered -fractures in which water seeps are larger -soil subsides to into widening voids -these depressions usually have shallow gentle slopes
Karst Topography
-many areas of the world have landscapes that to large extent have been shaped by the dissolving power of groundwater -usually areas underlain with limestone -usually contain sinkholes or sinks -occurs more in tropical climates due to lots of rain that can dissolve
Subsurface Environment
-not solid -includes countless tiny pore spaces between grains of soil and sediment -also includes joints and fractures in the bed rock -these spaces underground add up to a lot of volume
High Plains Aquifer
-occupies large dry region from south dakota to west texas -this aquifer accounts for 30 percent of all groundwater withdrawn for irrigation in the country -evaporation rates are high and precipitation rates are low there is little water to recharge the aquifer
How geysers work
-occur where extensive underground chambers exist with hot igneous rock -cool groundwater enters and the surround hot rock heats the water -at the bottom of the chamber the water is at great pressure because of the overlying weight of the water on top -the great pressure prevent the water from boiling so soon -heat cause the water to expand and forces some water out -the loss of water reduces the pressure on the water still in the chamber, lowering the boiling point -the water deep in the chamber quickly turns to steam and the geyser errupts -cycle occurs over and over
Geyser deposits
-once geyser erupt material in the solution often precipitated -producing a accumulation of sedimentary rock
Aquifers
-permeable rock strata or sediment that transmit groundwater freely -ex. Sand and Gravel
Groundwater contamination
-pollution of groundwater is serious -one common source of groundwater pollution is sewage -highway salt -fertilizers -pesticides -chemicals that leak from pipes etc -polluted water can go undected for a long time -once a polluted water supply is found the best thing to do is just regard it and allow the groundwater
Permeability
-pores must be connected to allow the water to travel and flow -its ability to transmit fluid -the groundwater twist and turns the interconnected openings -the smaller the pore space, the slower the water moves
Capillary Fringe
-right above the water table -ground water is held by surface tension in tiny passages between grains of soil and sediment
Artesian Wells
-self water rising wells -water rises without being pumped sometimes overflowing at the surfaces -abundant in northern france
Sewage Water
-sewage water that is contaminated with bacteria that enters the groundwater system can be purified through nataural processes by the sediment which percolates the bacteria -for purification to occur the aquifer must be of right compostion so containing lots of sediment so they water can be filtered and cleansed
Movement of Groundwater
-slow process -moves from pore to pre -most people think the groundwater travels in underground rivers, which isnt true
Groundwater
-some think it is renewable resource because it can be replenished by rain fall and snow melt -but in some areas it needs to be treated as a nonrenewable source because the amount of water availble to recharge the aquifer is less than the amount being withdrawn
Springs
-source of water is from zone of saturation and precipitation -when the water table intersects earths surface a natural outflow of groundwater results -usually happens when an aquitard blocks the groundwater from moving downward, so the water just moves lateral
Tower Karst
-steep sided hills that rise abruptly from the ground -groundwater has dissolved so much limestone it only leaves these tower standing
Losing Stream
-streams may loose water to the groundwater system by outflow through the stream bed -the elevation of the water table must be lower that the surface of the stream -can be connected to the groundwater system by a continuous saturated zone -or they can be disconnected from the groundwater system by an unsaturated zone could cause a bulge
Gaining Streams
-streams that gain water from the inflow of groundwater through the stream bed -elevation of the water table must be higher than the level of the surface of the stream
Ground Water
-subsurface pore spaces saturated with water and store the water -collects and moves through the pore spaces underground -one of our most important and widely available sources -environment is largely hidden from view except when in caves or mines -is found everywhere and can help poor countries who dont have water
Land Subsidence
-the ground may sink when water is pumped from wells faster than natural recharge processes can replace it -happens a lot in areas thick layers of sediments -as the water drops so does the pressure causing the sediment to take on more weight and compacting of the sediment causing the ground to subside -caused by ground water withdrawl
Saltwater Contamination
-the groundwater resource is being threatened by encroachment of saltwater - when the depth of freshwater below sealevel is about 40 times greater than the elevation of the water table above sealevel -there fore if groundwater with drawls continue to exceed recharge there will come a time when the elevation of saltwater will be high enough to be drawn into wells -deep wells and wells near the shore are the first to be affected
Porosity
-the quantity of groundwater depends on -percentage of the total volume of rock or sediment that consist of pore spaces -sediment is usually quite porus
Cone of Depression
-the result from a drawdown -conical shape -increase the hydraulic gradient near the well -groundwater flows more rapidly to the well
Hydraulic Gradient
-the steeper the slope the faster the water moves -because the steeper the slope the greater pressure difference between two points -the water table slope is known as -created by henry darci
Stalacites
-these icicle like pendants hang from the ceiling of the cavern -form where water seeps from cracks above -when the water reaches the air some carbon dioxide escapes the drop and calcite precipitates -depostion occurs as a ring around the edge of the water -each drop of water leaves a ring of calcite behind -then a hollow limestone tube is created -also called a soda straw
Igneous and Metamorphic Rocks
-usually have tightly interlocking crystals so very little voids -in these type of rocks fractures and joints have to provide the porosity
Hot Spring
-usually the water is 10 to 15 degrees warmer than the air -groundwater circulates at great depths, becoming heated -if the hot water risies rapidly to the surface it may emerge as a hot spring -more than 95% are found in the west
Speleothems
-various dripstone features found in caverns -no two are exactly alike
Pore Spaces
-water sinks into the ground because bedrock, sediment and soil contain countless voids or openings called -depend on the size and shape of the grain, how they are packed together , degree of sorting
Confined Aquifer
-when aquitards both above and below the aquifer must be present to keep the water confined and not allow it to escape -when the aquifer is tapped all the pressure that was being held there shoots the water up the well
Equalizer of stream flow
-when rain falls the water is soaked into the ground -then it moves slowly to different stream channels -thus the groundwater is a form of storage that sustains streams during periods when rain does not fall
Drawdown
-whenever water is withdrawn from a well the water table surrounding the well is lowered -decreases with the increase of distance from the well - if to much water is drawn from the well a very wide and deep cone of depression is formed and can lower the water table making other wells dry up
Column
-with a lot of time a downward growing stalacite and upward growing stalagmite may join to form a
Permeable
Aquifer composed of ______ sandstone or sand: -filters and purifies water very fast because it travels through the sediment making contact
Extremely Permeable
Aquifers composed of _____________ ______________ rocks like coarse gravel or limestone: -doesnt filter the water very good because it allows the water to travel to fast not making enough contact
Above and Below
For an Artesian system to exist: 1. Water is confined to an aquifer that is inclined so that one end can receive water 2. Aquitards must be __________ ____ ______ the aquifer to prevent the water from escaping.
Saltwater
Freshwater is less dense than
Rock
Ground water dissolves:
16 Million
How many water wells in the United States
Carbonic
Most Groundwater contains: - __________ acid -because rainwater readily dissolvves it from the air and from decaying plants
Flowing Artesian Well
Pressure surfeace is above ground level
Irrigation
Primary ways groundwater is used: -________ is the way most ground water is used - Public and domestic for indoor and outdoor household purposes like bathing, washing, cooking, lawns, and gardens -used for fish farms and aquaculture
Vegetation
Some influential Factors of Water soaking into the ground: -the steepness of the slope -nature of surface material -intensity of rainfall -type and amount of _______
Nonflowing Artesian Well
The pressure surface is below ground level
Stalacites and stalagmites
Two types of speleothems
Sink Hole
Water dissolves rock such as limestone which allows surface depressions to form
Low Pressure
Water moves towards areas with:
Ground water
What is the largest reservoir of freshwater that is readily available to humans?
52%
What percentage of stream flow is contributed by groundwater?
Polluted
What to do if you find ________ groundwater: -polluted water can go undected for a long time -once a polluted water supply is found the best thing to do is just regard it and allow the polluntants to be flushed away gradually -the aquifer must be unused for years -sometimes people pump out all the water and treat it themselves
Porosity and Permeability
What two factors influence the rate of ground water movement?
Ground water
__________ _______ is an important erosional agent; it dissolves rock, creating cavers and sink hols
Poorly Sorted
__________ _________ sediments usually have little porosity because the smaller grains tend to fill the openings among the larger grains
Hydraulic Gradient Formula
gradient formula elevation of point 1- elevation of point 2 divided by the distance between the two points