1GY 301: GeomorphologyGY 301: GeomorphologyLecture 20: GroundwaterUNIVERSITY OF SOUTH ALABAMAhttp://wedc.lboro.ac.uk/dw/images/drawing-water-from-a-well-1.jpgLast TimeKarst Geomorphology • What is karst?; Chemical considerations• Karst landforms (small to large scale)• Karst features on topographic mapsKarst Geomorphology• First described by Serbia Geographer Jovan Cvijić (1865–1927) • Named after the Kras Plateau region bordering Italy and the former Yugoslavia (now Serbia)• Distinctive landforms caused by dissolution of limestone by water (surface and ground water)CaCO3Ca2++ CO32-←→Chemical Considerations•The relationship between PCO2and Ca2+/CO32-is non-linear•Mixing any 2 waters that are naturally saturated with Ca2+and CO32-will result in a solution that is undersaturated (e.g., dissolution of CaCO3)Thrailkill (1968)Karst Topography• Limestone dissolution features are abundant and diverse both at the surface and undergroundKarst Topography•Like meandering rivers, the degree of karstification can be related to “age”2Karst TopographySmall Scale•rillenkarren (karren)•solution pits•pavementsKarst TopographyLarge Scale•caves•sinkholes•disappearing streams•tower karsthttp://www.devsys.co.uk/Album/Places%20of%20Interest/limestone%20caves.jpgKarst TopographyLarge Scale•caves•sinkholes•disappearing streams•tower karstKarst Features on MapsCavesToday’s LectureGroundwater • The hydrosphere and the hydrological cycle• Groundwater concepts• Hydrogeology concepts (Darcy’s Law, 3 point problems)HydrosphereThe hydrosphere is defined as all the water above, one and in the Earthhydrospherehydrosphere3Hydrological CycleWater in the hydrosphere is circulated within the hydrological cyclehttp://www.coloradocollege.edu/dept/ev/courses/EV211WWW/hydrological%20cycle.jpgHydrological CycleMost of the planet’s water is in the oceans (96%) followed by the ice caps (3%) and then groundwater (1%)http://www.coloradocollege.edu/dept/ev/courses/EV211WWW/hydrological%20cycle.jpgGroundwaterGroundwater is water that infiltrates below the Earth’s surfacePorosity: percent void space in a materialPermeability: degree of connectivity of pores (ability of a material to transmit a fluid)Common permeable geological material includes sandstone, limestone, marble, fault brecciahttp://www.belmont.sd62.bc.ca/teacher/geology12/photos/erosion-water/permeability.gifWater TableThe water table is a planar surface that separates the saturated and undersaturated zones http://myweb.cwpost.liu.edu/vdivener/notes/water_table.gifWater TableThe water table is a planar surface that separates the saturated and undersaturated zones http://myweb.cwpost.liu.edu/vdivener/notes/water_table.gifUndersaturated zone (Vadose)Straight down water movementSaturated zone (Phreatic)Lateral? water movementWater Table Morphology• The water table is a subdued replica of the overlying topographic surfacehttp://earthsci.org/education/teacher/basicgeol/groundwa/chwattab.gif4Water Table Morphology• Where the water table intersects the surface there will be a water discharge (spring, pond, lake or stream)http://earthsci.org/education/teacher/basicgeol/groundwa/chwattab.gifWater Table Morphology• Porous layers that area capable of passing water and releasing it at springs and/or wells are called aquifers.http://www.tol.ca/files/web_images/engineering/environment/WebImages/unconfined.jpgWater Table Morphology• Clay layers may act as aquicludes and generate a perched water table (a localized water table).Water Table Morphology• The recharge area is where the precipitation enters the groundwater systemhttp://groundwater.oregonstate.edu/sites/default/files/u1/rechargeb.gifTypes of Aquifers• Unconfined Aquifer: open to direct recharge at the Earth’s surface• Confined Aquifer: bracketed by aquicludes (impermeable) • Potentiometric Surface: elevation to which the pressurized water in a confined aquifer will rise• Artesian Well: water rises to an elevation above the aquifer• Flowing Artesian Well/Spring: potentiometric surface is above the ground surfaceTypes of AquifersPotentiometric Surface: elevation to which the pressurized water in a confined aquifer will riseArtesian Well: water rises to an elevation above the aquiferFlowing Artesian Well/Spring: potentiometricsurface is above the ground surfacehttp://www.douglas.co.us/water/images/Denver_Basin_Aquifers_clip_image004.jpg5• Pumping lowers the elevation of the local water table (Drawdown)Anthropogenic Effects Anthropogenic Effects• Excessive pumping can severely lower the elevation of the local water table (cone of depression)http://myweb.cwpost.liu.edu/vdivener/notesAnthropogenic Effects• Which can really be bad during droughts (wells run dry)Water Resources• Potable groundwater is a rapidly diminishing resourceOther Groundwater Issues• Ground subsidence and collapse Sinkholes• Saltwater intrusion: Salt water is more dense than fresh waterOther Groundwater Issues6• Contamination of groundwater supplyOther Groundwater Issues Contamination Issues• Lead (Pb): sources include atmospheric pollution and older lead pipes• Radioactive Waste: natural and anthropogenic sources• Microorganisms: sewage and waste water, flooding and storm surge• Other chemical contaminants (solvents, gasoline, nitrates, road salt, etc.)Hydrothermal Systems• Groundwater heated by magmatic sourcesGroundwater Flow (J. Connors Stuff)• Darcy’s Law: governs the volume of groundwater produced at a well headQ= A(K x h)– Q is volume – A is cross sectional area of aquifer– K is permeability– h is hydraulic head– l is map distanceli.e., you can determine groundwater flow ratesGroundwater Flow (J. Connors Stuff)Three Point ProblemCalculate the direction of groundwater flow based upon water table elevationsWater flows from high elevations to low elevationshttp://www.uwgb.edu/dutchs/Graphics-Geol/structur/manual/fig13a.gifGroundwater Flow (J. Connors Stuff)Three Point ProblemCalculate the direction of groundwater flow based upon water table elevationsChalk BoardSinkhole(WE=425 ft)Spring(440 ft)WellSurface elevation: 474 ftDept to water: 100 ft7Upcoming StuffHomeworkArid Lands Geomorphology (due Friday)Next Lecture: GlaciersFriday’s Lab: Map interpretation