GroundwaterQuestions to ponderPowerPoint PresentationHydrologic Cycle Precipitation = Evaporation + Infiltration + RunoffInfiltration = GW RECHARGEAt some point in depth, all rocks and/or soil become completely saturated with waterSlide 7Slide 8Slide 9Porosity and Permeability - Rock PropertiesSlide 11Slide 12Slide 13Slide 14Slide 15Slide 16Permeability - Flow through connected pores or fracturesHow groundwater systems function2 Categories of AquifersSlide 20Unconfined aquifersSlide 22Slide 23If the water table intersects the surface, it is a Discharge ZoneUnconfined aquifers often follow topographyConfined aquifersSlide 27Confined and unconfined aquifersGroundwater issuesSurface water and groundwater may be in contactSlide 31Rates of Groundwater movementSlide 33Slide 34Water wellsSlide 36Water can be over consumedSurface water can be impacted affecting ecologySubsidence – the lowering of ground elevation can be caused by excess water removalSlide 40Erosion by GW and formation of CavesSlide 42Slide 43Slide 44Requirements for Karst TopographyFormation of Karst TopgraphySlide 47Slide 48Slide 49Cave formations (Speleothems)Slide 51Cave formations (Dripstones)Thermal (Hot) SpringsSlide 54Slide 55Slide 56Slide 57GroundwaterGroundwaterLecture 32Lecture 32Questions to ponder•How does geologic material hold and move water? What characteristics of the rocks makes this possible?•Why is groundwater so important yet so fragile of a resource?•What are groundwater issues and problems?•How does Karst topography form, what are the features and how does this relate to erosion?Hydrologic CyclePrecipitation = Evaporation + Infiltration + RunoffInfiltration = GW RECHARGE–Gravity is primary driving force•Pulls water down into soil/rock–Water enters the system at the ground surface through recharge•Recharge from infiltration–Precipitation, Wetlands, lakes and streams–Leaves the system through discharge•Springs, seeps,•Wetlands, lakes and streamsAt some point in depth, all rocks and/or soil become completely saturated with waterWater TableUnsaturatedzoneSaturatedzoneThe Water Table•Water is found at some depth everywhere beneath the Earth’s surface•The water table defines the boundary below which all pore spaces are filled with water•The volume of pore spaces decreases as you go deeper into the crust•Usable water is restricted to a few hundred meters below the surfacePorosity and Permeability- Rock Properties•Porosity – is the amount of void spaces in rock or soil.–Relates to how much liquid (or gas) geologic material can hold–Percentage of the volume•Permeability is the connectedness of these pore spaces–How easily fluids move through geologic materialPorosity•Percent of the total volume that is open space•Affected by the size and shape of particles•Increased by fracturing or dissolution•Decreased by compaction and cementation•Well sorted sediments have higher porosity than poorly sorted sedimentsPermeability•How easily fluid may pass through a rock–A measure of how well the pores are connected, and how straight a path a fluid follows•Permeability is a property of the rock–Controls the ability of water to flow through a rock or soil–Other liquids such as oil flow through rock–Density and viscosity influence flow ratePermeability -Flow through connected pores or fracturesHow groundwater systems function•If Soil or Rock has High Porosity and High Permeability and we can extract usable water it is called an AQUIFER•If Soil or Rock has a Low Permeability (regardless of porosity) & cannot conduct fluids and is called AQUICLUDE or AQUITARD–Fine grained, and Platy minerals such as Clays, and rocks such as Shale prohibit the flow of water2 Categories of Aquifers•UNCONFINED Aquifers–Open to the surface–Usually defined by the beginning of the Water Table•CONFINED Aquifers–Separated from direct connect to the surface by a confining layer of impermeable material called an AQUICLUDEUnconfinedaquiferConfined aquiferUnconfined aquifers•The depth to the water table varies with response to rainfall–Can be near the surface during wet seasons; Deeper during dry periods•The shape of the water table (and unconfined aquifers) generally follows topography•Water flows always in response to gravity•Recharge zones are across a broad surfaceIf the water table intersects the surface, it is a Discharge Zone•Surface water in may be in contact with the groundwater–”Unconfined aquifers often follow topographyConfined aquifers•Don’t necessarily follow topography•Water flows in response to Pressure that develops•Separated by Impermeable material•Many separate confined aquifers can exist in a given area (By definition, only 1 Unconfined aquifer will be encountered)•Recharge zones may be narrow and limitedArtesian Wells may develop if Pressure is high enough to make water rise above the elevation of AquiferConfined AquifersConfined and unconfined aquifersGroundwater issues•Pollution•Rates of movement•Problems from Overconsumption•KarstSurface water and groundwater may be in contact•Springs, seeps, (Discharge)• wetlands, lakes, streams (recharge or discharge)•Implications for many things–Development–Natural resources–Pollution migrationRates of Groundwater movement•Depends on Permeability•Rates often very slow–From several centimeters/day to millimeters per year•“Age” of some groundwater supplies can be 10’s of years to millions of years.Darcy’s LawThe rate the water flows between two points is directly proportional to the drop in slopeWater wells•Artificial discharge•Often we remove more water than can flow through the rock/soil–“Cones of Depression” develop•Worse yet, we can remove more water than can be recharged–Leads to major problems: Depletion of resource, changes in ecology, Salt water intrusion, SubsidenceWater can be over consumedSurface water can be impacted affecting ecologySubsidence – the lowering of ground elevation can be caused by excess water removalElevation lossElevation lossFissuresFissuresAquifers becomecompacted after water is removedErosion by GW and formation of Caves•Groundwater chemically weathers & erodes the bedrock through dissolution–Subsurface dissolution forms:•Caves•Sinkholes•Karst topographyKarst Topography•Karst topography is found in areas that have carbonate, sulfate, or salt beds at or near the ground