chapter fifteen groundwater
DESCRIPTION
Chapter Fifteen Groundwater. Groundwater. Earth’s hydrosphere extends from top of atmosphere to ~ 10 km (6 mi) below the Earth’s surface. Groundwater, 0.6% of world’s water, accounts for 97% of Earth’s supply of unfrozen water. - PowerPoint PPT PresentationTRANSCRIPT
Chapter FifteenChapter FifteenGroundwater Groundwater
GroundwaterGroundwater Earth’s hydrosphere extends from top of atmosphere to ~
10 km (6 mi) below the Earth’s surface. Groundwater, 0.6% of world’s water, accounts for 97% of Earth’s supply of unfrozen water.
Surface waters from rivers, lakes or precipitation enter the ground under the influence of gravityThe amount of water that enters the ground depends on
the topography, geologic composition and vegetation The surface water will percolate downwards until it
reaches a zone where all the pore spaces are saturated with water
Factors affecting infiltrationFactors affecting infiltration
Moisture through treeMoisture through tree
Surface distribution of waterSurface distribution of water
Movement and Distribution of GW Movement and Distribution of GW
Water bound to clay mineralsZone of aeration: unsaturated zoneZone of SaturationWater Table: Upper surface of the zone of
saturationCapillary Fringe: Lower part of the aeration zone –
range from few tens of cm to several meters
Groundwater MovementGroundwater Movement For groundwater to flow- need porous and permeable
materials Porosity is the percent of pore spaces in relation to the total
soil/rock/sediment volume (Primary Porosity: Porosity that develops as a rock forms; Secondary Porosity: Develops after a rock has formed)
Permeability is a measure of the ability of rock/sediment to transmit fluid
Groundwater flow occurs when there is a hydraulic gradient Hydraulic conductivity is the ability to transmit groundwater.
Typical groundwater flow is slow ~0.5 – 1.5 cm/day (0.2 - 0.6 in/day). The slow movement stores the water making it available to humans.
The subsurface distribution of waterThe subsurface distribution of water
Primary porosity of sedimentary rocksPrimary porosity of sedimentary rocks
Pore connection and PermeabilityPore connection and Permeability
Pore connection and Permeability – contd.Pore connection and Permeability – contd.
Hydraulic gradientHydraulic gradient
Variations in water table depthVariations in water table depth
Water Table configurationWater Table configuration
Perched water poolsPerched water pools
Tapping Groundwater aquiferTapping Groundwater aquifer Groundwater depth is a reflection of local topography
and prevailing climate Aquifers are permeable water-bearing bodies of
geologic materialsUnconfined and Confined aquifers
Aquiclude and Aquitard Artesian flow- water flows to the surface from wells
without pumpingPotentiometric surfaceNatural SpringsGeysers- intermittent surface emission of hot
water/steam
How groundwater flowsHow groundwater flowsGroundwater flow potential
– Gravity– Pressure from overlying water and rocks– Hydraulic Gradient: Difference in potential / distance– Hydraulic conductivity: Measure of conductivity –
size, shape & degree of sorting of its grains – coarse, well-rounded, well-sorted and gravel – high conductivity
– Darcy’s principle (19th Century): Rate at which water flows is difference in potential
hydraulic conductivity
Groundwater flow – contd.Groundwater flow – contd.Mesuring the Rate of GW Flow:
– Dye injection method– Carbon –14 dating method
Groundwater Flow Rate:
Average: 0.5 to 1.5 cm/day
Fastest: 100 m / day
Composite LandscapeComposite Landscape
Artesian aquiferArtesian aquifer
Desert OasesDesert Oases
Municipal water towerMunicipal water tower
Natural springsNatural springs
Natural springs – contd.Natural springs – contd.
GeysersGeysers
Locating groundwater and features associated with pumpingLocating groundwater and features associated with pumping
Locating GroundwaterMapping
Water table from well records, lake, river levels, drilling test holes
Features Associated with PumpingCone of depression- local depression in water around
pumping well Subsidence- compressed land due to aquifer depletionSalt water intrusion- due to over pumping along coast line
Greater demand for water- leads to groundwater depletion and introduction of pollutant
Solutions- enhance recharge, water transfer, conservation, desalinization, and use of iceberg
Search for GroundwaterSearch for GroundwaterCharacteristics of the Water Table:
– Depends on Typical depth– Relationship to topography– Response to Climatic Fluctuations
AQUIFERS:– Aquifer: Permeable, water-bearing bodies of
geological material– Unconfined aquifer: Not overlain by impermeable
cap tock– Confined Aquifer: Found in greater depths, between
aquiclude (impermeable rock layers) and Aquitard
Search for waterSearch for water
Overuse of groundwaterOveruse of groundwater
Water table around a wellWater table around a well
The effect of development on a water tableThe effect of development on a water table
Subsidence in a coastal areaSubsidence in a coastal area
Subsidence in a coastal area – contd.Subsidence in a coastal area – contd.
Groundwater contamination / purificationGroundwater contamination / purification
Natural occurring solutes- Chlorine, Arsenic, Mercury, and Selenium
Manufacturing contaminants- from household products: cans of paint, solvent, cleanser etc.
Natural Groundwater PurificationFiltration- adhere to clay particlesDecomposition- some decompose completely
by oxidationBacteria action- organic solids consumed by
microorganis
Saltwater intrusionSaltwater intrusion
Salt water intrusion – contd.Salt water intrusion – contd.
Stratigraphy of Yucca MountainStratigraphy of Yucca Mountain
Landfill sitesLandfill sites
Landfill sites – contd.Landfill sites – contd.
Products of GroundwaterProducts of Groundwater Karsts
Water reacts with carbon dioxide to form weak carbonic acid which then attacks limestone
H2O + CO2 => H2CO3 + CaCO3 => Ca++ HCO3 –
Caves- natural underground cavities and most common geological product of limestone dissolution
Cave deposits- spelotherms are deposits on cave surfaces in a variety of forms: travertine, Stalactite, Stalagmite, banded draperies or drip curtains
Growth of spelotherm- depends on the solution and porosity of surface material, climate, topography, and vegetation
State 1 of cave formationState 1 of cave formation
State 2 of Cave formationState 2 of Cave formation
Stalactite, stalagmite and travertineStalactite, stalagmite and travertine
Cave formationCave formation
Speleothem growth and climateSpeleothem growth and climate
Rise and fall of sea levelRise and fall of sea level
Karsts TopographyKarsts Topography
Surface expression of the geology of dissolved limestone and work of near surface water
Cave and Karsts landscapes are extremely sensitive- so need to be protected
LandformSinkholes-circular surface depressionDisappearing Streams- flow through sinkholes may
emerge as spring several kilometers awayNatural Bridge- series of neighboring sinkholes
expand and join together
Worldwide distribution of karst landformWorldwide distribution of karst landform
Typical landforms associated with karst topographyTypical landforms associated with karst topography