9.2 - Groundwater.pdf

11,. -'!'_.. ,, -- ,, I, ~ ,, l f I' l ~; ' '• >Jr, o/5,7 • • • A valuable natural resource that provides about half of our drinking water and is essential to the vitality of agriculture and industry. Considering the entire hydrosphere, or all of Earth's water, only about sixtenths o...

11,. -'!'_.. ,, -- ,, I, ~ ,, l f I' l ~; ' '• >Jr, o/5,7 • • • A valuable natural resource that provides about half of our drinking water and is essential to the vitality of agriculture and industry. Considering the entire hydrosphere, or all of Earth's water, only about sixtenths of 1 % occurs underground. Groundwater represents the largest reservoir of fresh water that is readily available to humans Source: https://www.rese archgate. net/figur e/Hypotheticalsurfacegroundwatersystem-Adaptedfrom -CalifomiawaterfoundationJig1_2 82450672 HDA. Reyes I Principles of Geology • Distribution of Groundwater □ Zone of soil moisture < - ~ /////// ✓ Refer to the zone where water trapped in the soil horizon for biological use such as plants. l □ Zone of saturation ✓ Water that is not held as soil moisture will percolate downward until it reaches a zone where all of the open spaces in sediment and rock are completely filled with water. infiltration Unsaturated (Vadose) zone ,-capillaryfringe .......::::: WATE R TAB LE Saturated Zone Source: https://imnh. iri.isu. edu/digita/at/as/hydr/con cepts/gwater/gwtrvw. htm ✓ Groundwater HDA. Reyes Soil Moisture I Principles of Geology • Distribution of Groundwater □ Water Table ✓ The upper limit of < ~ /////// zone of saturation □ Unsaturation Zone (Vadose Zone) ✓ The area above the water table where the soil, sediment, and rock are not saturated ✓ The pore spaces in this zone contain both air and water. ✓ Water cannot be pumped by wells because it clings too tightly to rock and soil particles HDA. Reyes l infiltration Unsaturated (Vadose) Zone Soil Moisture ,-capillaryfringe .......::::: WATE R TAB LE Saturated Zone Source: https://imnh. iri.isu. edu/digita/at/as/hydr/con cepts/gwater/gwtrvw. htm I Principles of Geology • The Water Table □ Stream and Groundwater interaction ✓ Gaining Stream A GAINING STREAM B LOSING STREAM Flow dlroctloo •!• Streams may gain water from the inflow of groundwater through the stream bed. ~ r r u S.turated zone C LOSING STREAM THAT IS DISCONNECTED FROM THE WATER TABLE •!• The elevation of the water Flow dlrecllon table must be higher than the level of the surface of the stream. http ://pubs.usgs.gov/circ/circl 186/html/gw_ effect.html HDA. Reyes I Principles of Geology --=--- • The Water Table □ Stream and Groundwater interaction A ✓ Losing Stream (Connected) ✓ Losing Stream (Unconnected) GAINING STREAM B LOSING STREAM Flow dlroctloo _ -.....-+-,,.---- r r •!• Streams may lose water to the groundwater system by outflow through the stream bed. u S.turated zone C LOSING STREAM THAT IS DISCONNECTED FROM THE WATER TABLE Flow dlrecllon •!• The elevation of the water table is lower than the surface of the stream. http ://pubs.usgs.gov/circ/circl 186/html/gw_ effect.html HDA. Reyes I Principles of Geology • Factor Influencing the Storage and Movement of Groundwater no unconnected connected pore spaces pore spaces pore spaces non . .porous porous porous non-permeable non-permeable permeable □ Porosity ✓ The percentage of the total volume of rock or sediment that consists of pore spaces. □ Permeability ✓ ability a material Source: https://www.un om aha. edu/internationa/-studies-and-programs/center-for-afghanista nstudies/academics/transboundary-water-research/DLM15/DLM15 .php to transmit a fluid. HDA. Reyes I Principles of Geology • Factor Influencing the Storage and Movement of Groundwater □ Aquitard ✓ Impermeable layers that hinder or prevent water movement. Area of reeharge fo1 aq;ultar □ Aquifer ✓ • !t•.., ~ Pe rm ea b Ie rock st rat a ~~~~.:.:;.·.~ --~-~i':7~ ~ :;;::f~ ~ ~ ~ ~ ~ ~ , , , Shafe Sandstcme or sediments that a_quiciudes aquifer transmit groundwater © 1SS8 Wadsworth Publishing CompanyllTP 1 freely HDA. Reyes I Principles of Geology • How groundwater moves □ Simple Groundwater Flow System Water table ✓ groundwater moving along flow paths from areas of recharge to a zone of discharge along a stream. ✓ Discharge also occurs at springs1 lakes1 or wetlands1 as well as in coastal areas as seeps into bays or the ocean. ✓ Transpiration by plants whose roots extend to near the water table represents another form of groundwater discharge. HDA. Reyes Stream FtGURE 10.8 Arrows indicate groundwater movement through uniformly permeable material. The looping curves may be thought of as a compromise between the downward pull of gravity and the tendency of water to move toward areas of reduced pressure. I Principles of Geology • Measuring Movement Groundwater □ Hydraulic Gradient ✓ Water-table slope ✓ French engineer scientistHenri Darcy ✓ Where hl 1s the elevation of one point on the water table, h2 is the elevation of a second point, and d 1s the horizontal distance between the two points HDA. Reyes I Principles of Geology • Measuring Groundwater Movement □ Hydraulic Gradient ✓ Darcy also discovered that the flow velocity varied with the permeability of the sediment-groundwater flows more rapidly through sediments having greater permeability than through materials having lower permeability. ✓ Hydraulic conductivity (Q) Q = KA(h 1 - h2 ) d \'llh£re h - h1 L d LS lhe hydraulic gradient, K • is the c .. ffic1ent Lh at represents hydraulic cond ucLivit)' and A is the cross-sectional area or the aquffer. This e:!-..-presslon has come Lo be called Darc-1'~ law. 1 HDA. Reyes I Principles of Geology • Springs □ A natural outflow of groundwater □ It was formed whenever the water table intersects Earth's surface □ It was also form when an aquitard blocks the downward movement of groundwater and forces it to move laterally. Source: http://www.almostafarmer.com/groundwater-wells/ HDA. Reyes Ground \/later di srnarges from springs in the Grand Can-yon. Credit: R.D .MacNish, USGS I Principles of Geology • Springs □ Perched water table ✓ As water percolates downward, a portion of it is intercepted by the aquitard, thereby creating a localized zone of saturation . Source: http://corbinarts.c om/editor/? HDA. Reyes I Principles of Geology • Wells □ A hole bored into the zone of saturation □ Drawdown ✓ When water 1s withdrawn from a well, the water table around the well 1s lowered; Decreases with increasing distance from the well. □ Cone of Depression ✓ A depression in the water table, roughly conical in shape. I Water table Before heavy pumping FIGURE 10 11 Wells ore lhe most common means by which people acquire - -- groundwater A cone of depre~,ion 1n the water table ohen forms around a pumping well. If heavy pumping lowers the water After heavy pumping rable, acme wells rnay be left dry. (Photo by ASPIYPP/agefotostodc) HDA. Reyes I Principles of Geology cf\ ~s9,.-- r o: ~ - - Lowered water table • Artesian Wells □ Applied to any situation in which groundwater rises in a well above the level where it was initially encountered. 1. 2. Water is confined to an aquifer that is inclined so that one end is exposed at the surface, where it can receive water. Aquitards, both above and below the aquifer, must be present to prevent the water from escaping. Such an aquifer is called a confined aquifer. HDA. Reyes I Principles of Geology • Artesian Wells □ Nonflowing artesian well □ Flowing artesian well □ Artesian springs FIGURE 10. 12 Artesian s~ems occur when an mclined aquifer 1s surrounded by impermeable beds (aquitards), Such aquifers are called a confined aquifers The photo shows a flowing artesian well (Photo by Jamlils E. Patte~on) Aqultard Confined aquifE - Aquitard Nonflo\vlng artesian well (water must be pumped from pressure surface to surface) Pressure surface HDA. Reyes I Principles of Geology • Problem Encountered with Groundwater □ Land subsidence caused by groundwater withdrawal □ Groundwater Contamination rtcWeilean2water deli\'BmQ t W$r table FIGURE 10. 16 A. Although the contaminated 11,1awr has !raveled more than 100 meters before reaching Well 1, th.e water moves too rapidly through lhe cavernOlJs limestooo to be purified. B. As the discharge from the septic tank percolates through lhe pem,eable sandstone, it 1s purified in a relatively short d istance_ HDA. Reyes I Principles of Geology • Hot Springs and Geysers □ Geysers ✓ When the water contains dissolved silica, a material called siliceous sinter or geyserite is deposited around the spring. ✓ When the water contains dissolved calcium carbonate, a form of limestone called travertine or calcareous tu/a is deposited. Source: https;//ww ~ w.nps.gov/ ,.. features/ye 11/ofvec/ex hibits/erup tion/water /runoff.ht Source: http://ww w.theworld isabook.co m/4889/tu fa-towersat-mono/ake/ m HDA. Reyes I Principles of Geology • Hot Springs and Geysers □ Geysers ✓ Many people think that Old Faithful erupts so reliably-every hour on the hour-that you can set your watch by it. So goes the legend, but it's not true. Time spans between eruptions vary from about 65 minutes to more than 90 minutes and have generally increased over the years thanks to changes in the geyser's plumbing. Source: https://ww w.yel/owst onepark. co m/thingstodo/abouto/d-faithful HDA. Reyes I Principles of Geology • Geothermal Energy □ Harnessed by tapping natural underground reservoirs of steam and hot water. □ These occur where subsurface temperatures are high, owing to relatively recent volcanic activity. □ Geothermal energy is put to use in two ways: 1. 2. The steam and hot water are used for heating to generate electricity HDA. Reyes I Principles of Geology • Geothermal Energy THI GfOF N FRGY Top 1O Countries - installed capacity United States 3,442 Philippines 1,968 Indonesia 1,339 Mexico 1,005 New Zealand 961 Italy 941 Iceland 66.'5 Kenya 607 Japan 502 Turkey 410 1,142 Other 0 Thri<CeoCnergy - Ja,umy 2015 500 1,000 1,500 2,000 Sour<>,1: TI1lukG.,.,E,1.,.gy Researcll, GEA, IGA (2015) HDA. Reyes I Principles of Geology 2,/100 8,000 8,/100 :J • Geothermal Energy □ Factors needed to find a potential site. 1. 2. 3. geothermal A potent source of heat Large and porous reservoirs with channels connected to the heat source A cap of low permeability rocks ------ ---_,,,,,,/ / / ~ \mpermeable 1ocll -------- (thermal col\CltA,bon) _,,,- Source: http://rodopinews.gr/6546 HDA. Reyes I Principles of Geology Flowofheol (conducbon) • Landform crafted by groundwater □ Cavern ✓ A cave, or a chamber in a cave, typically a large one. ✓ Caverns are created at or just below the water table in the zone of saturation. Source: https;//urbanscraw/dc.com/2017/01/04/try-this-cave-for-a-weekend-getaway/ HDA. Reyes I Principles of Geology • Landform crafted by groundwater □ Cavern ✓ Dripstone - calcium carbonate that is left behind produces the limestone ✓ Speleothems - Collective terms used for various dripstone features found in caverns. •!• Stalactites - icicle-like pendants hang from the ceiling of the cavern and form where water seeps through cracks above. "Soda straw 11• •!• Stalagmites - Speleothems that form on the floor of a cavern and reach upward toward the ceiling •!• Column - When stalactite and stalagmite connects or meets. HDA. Reyes I Principles of Geology • Landform crafted by groundwater Source: http://brid a/cave.blog spot.com/2 016/01/sta /actitesstalagmite s-which-iswhich.html HDA. Reyes I Principles of Geology • Landform crafted by groundwater □ Karst Topography ✓ A landscape that is characterized by numerous caves, sinkholes, fissures, and underground streams. ✓ Arid and semiarid areas are too dry to develop karst topography. •!• Sinkholes or sink - Karst areas typically have irregular terrain punctuated with many depressions. •!• Tower karst- Isolated tower of carbonate rocks. HDA. Reyes I Principles of Geology • Landform crafted by groundwater Caves form just below the water table. Water- • table □ Karst Topography •!• Sinkholes or sink (al Dissolution takes place near the water table in an uplifted sequence of limestone. Old cave:, empty; speleothems grow. Water table sinks; 11aw cavas form (bl Downcutting by an adjacent river lowers the water table, and the caves empty, Speleothems grow. Source: http://geo/ ogy/eam.bl ogspot.co m/2016/01 /cavesandkarst.html Caves collapse; kars\ landscape develops. nrne New caves get bigger. (cl /\fter roof collapse, the lanoscape becomes pockmarked w ,th sinkholes. HDA. Reyes I Principles of Geology • Landform crafted by groundwater □ Karst Topography •!• Tower karst 'I. Su•face straams lose water to cave systems developing m the limestone. Surface dr amage is diverted down sink holes to below the 2. Peaks develop from the land left aflea e,osion by the streams The cave system gets larger as fasl•moving subsurface strea,ms bore lhrough the limestone i and water table 'lhe waler table drops. Source: https;//www.flickr.com/photos/98531730@N02/9455307987 HDA. Reyes I Principles of Geology 3 Much ofthra limestone has eroded pasl the icave s down to a Ia,yer or shale. Umestone peaks remain. many fractured with sma,11 . wa1etless Ca¥8:S. Lutgens, F., Tarbuck, E. and Tasa, D. (2012). Essentials of Geology Eleventh Edition. Upper Saddle River, New Jersey: Pearson Prentice Hall. HDA. Reyes I Principles of Geology