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See all Premium member Presentation Transcript Chapter 11Ground Water: Chapter 11 Ground WaterHydrologic Cycle: Hydrologic CycleGlobal Distribution of Water: Global Distribution of WaterGround Water Topics: Ground Water Topics The Water Table Porosity and Permeability The Movement of Ground Water AquifersWater Table: Water TableGround Water Definitions: Ground Water Definitions Porosity: Volume percentage of rock that consists of voids or openings. It is a measure of the rock’s ability to hold water. Permeability: Capacity of a rock to transmit fluid through pore space and fractures. Rocks that allow water to flow easily are referred to as permeable, while those that do NOT are referred to as impermeable.Porosity and Permeability Table: Porosity and Permeability TableWater Table in quarry: Water Table in quarry Water TablePerched Water Tables: Perched Water TablesCauses of Ground Water Movement: Causes of Ground Water Movement Hydraulic head (h) = elevation + pressure Hydraulic gradient = difference in head/distance Water flows from zones of high hydraulic gradient to low hydraulic gradient! h.g. = h/LFlow Velocity and Potential: Flow Velocity and Potential Flow is always perpendicular to the lines of equal potential. Potential = acceleration of gravity • hydraulic head = g • h ~ hGroundwater Flow Velocity: Groundwater Flow Velocity Flow velocity is governed by Darcy’s Law Darcy’s Law states that the velocity is equal to the permeability times the hydraulic gradient, where permeability is the capacity of a porous material to transmit fluid. This gives the equivalent flow velocity through an open pipe. To correctly apply to real rocks, must divide by the porosity. Ground water velocity = perm./porosity • hydraulic gradient V = (K/n) • (h/L) where K is hydraulic conductivity (a measure of permeability) and n is porosity.Ground Water Movement in Permeable Rock: Ground Water Movement in Permeable Rock Within a uniformly permeable rock, water table tends to mimic surface topography. Flow usually parallels sloping water table.Aquifers: Aquifers Aquifer: body of saturated rock or sediment through which water can move easily. Examples: Sandstone, conglomerate, well-fractured limestone, bodies of sand and gravel Unconfined aquifer: water table is only partly filled. Confined aquifer: water table completely filled with water under pressure. Aquitard or aquiclude: body of rock with low permeability, which retards the flow of water across it.Confined vs. Unconfined Aquifers: Confined vs. Unconfined AquifersAdditional Ground Water Topics: Wells Springs and Streams Ground Water Contamination Balancing Withdrawal and Recharge Additional Ground Water TopicsWells: Wells Well: hole drilled into the ground to access ground water. May be drilled or dug and may require pumping to bring water from depth to surface. Cone of depression: conical feature in the water table that develops through well drawdown (removal of groundwater faster than recharge). Artesian well: is one in which flow of water reaches surface without the need of pumping. Must tap into a confined aquifer.Good vs. Poor Well: Good vs. Poor WellDry Well in Fractured Rocks: Dry Well in Fractured RocksChanges in Water Table with Rainfall: Changes in Water Table with RainfallDrawdown: DrawdownMississippi Alluvial Aquifer System: Mississippi Alluvial Aquifer SystemMississippi Alluvial Aquifer System: Mississippi Alluvial Aquifer System Major cone of depression with ~80 ft. decline in the equipotential surface since 1920’s DeWitt StuttgartSubsidence: SubsidenceArtesian Well Controls: Artesian Well ControlsArtesian Well: Artesian WellLarge Spring: Large SpringIntermittent Springs/Seeps: Intermittent Springs/SeepsSpring Controls and Types: Spring Controls and TypesGaining vs. Losing Streams: Gaining vs. Losing Streams Stream type controlled by changes in the water table. Gaining stream: ground water flow into stream Losing stream: water flows into saturated zone Eventually can produce dry stream!Sources of Ground Water Pollution: Sources of Ground Water Pollution Pesticides Household garbage and improperly installed or maintained septic systems Landfills Animal waste Industrial toxic wasteAnimal Waste: Animal WasteIndustrial Toxic Waste: Industrial Toxic WasteLandfill’s Impact on Ground Water Quality: Landfill’s Impact on Ground Water QualityIndustrial Pollution: Industrial PollutionSeptic Systems: Septic SystemsPollution Problems Aggravated by Pumping Wells: Pollution Problems Aggravated by Pumping WellsSalt Water Infiltration Animation: Salt Water Infiltration AnimationEffects of Ground-Water Action: Effects of Ground-Water Action Caves, Sinkholes, and Karst Topography Other Effects Ground subsidence Hot Water Underground Geothermal Energy Development of Karst in Limestone: Development of Karst in Limestone - Rainwater infiltration along cracks. - Reaction with limestone causing dissolution and acidification of groundwater. - Re-precipitation of dissolved calcite. - Lowering of water table. H2O + CO2 + CaCO3 = Ca++ + 2HCO3- Cave development Dripstone developmentCave structures: Cave structures Stalactites (roof) Stalagmites (floor) Dripstone or Speleothems are calcite deposits built by dripping ground water.Karst Topography and Structures: Karst Topography and Structures Karst is well developed in NW Arkansas!Shale concretions: Shale concretionsGeodes: GeodesGeyser Development: Geyser DevelopmentCalcite Precipitation and Formation of Travertine Terraces in Yellowstone: Calcite Precipitation and Formation of Travertine Terraces in YellowstoneGeyserite Deposits: Geyserite Deposits Steam venting Geyserite deposits Castle Geyser, YellowstoneGeothermal Plant: Geothermal Plant You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.