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Groundwater Science, James Beach
 

Groundwater Science, James Beach

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    Groundwater Science, James Beach Groundwater Science, James Beach Presentation Transcript

    • Groundwater Science Aquifers Wells etc.James Beach, PGLBG-Guyton Associates
    • Special thanks to Robert Mace of TWDB for many slides
    • Outline• big picture• technical definitions (sorta)• flow in aquifers• pumping an aquifer• miscellaneous important stuff
    • Groundwater in the World From Freeze and Cherry (1979)
    • Major aquifers
    • Minor aquifers
    • Texas groundwater factoids• 60% of the water used in Texas• 81% of groundwater is used for irrigation• groundwater provides 39% of water to cities
    • groundwater use in Texas (1937 to 2003)
    • TECHNICAL DEFINITIONS
    • Definitions• Aquifer• Aquitard/confining layer• Vadose zone/unsaturated zone• Water table• Recharge• Water level• Unconfined aquifer• Confined aquifer
    • what is an aquifer?• an aquifer is geologic media that can yield economically usable amounts of water.
    • Porous Media
    • Hickory Aquifer, sandstone
    • Edwards-Trinity (Plateau) Aquifer, limestone
    • Ogallala Aquifer, sand and gravel
    • what is an aquitard?• an aquitard is geologic media that can not yield economically usable amounts of water.
    • what is a confining layer?• A confining layer is an aquitard that bounds an aquifer.
    • the unsaturated zone Unsaturated zone
    • the water table Unsaturated zone
    • recharge
    • recharge – typical
    • recharge – not typical
    • the water level
    • water flows down gradient(to lower potential energy)
    • Groundwater Flowpaths (TOP view)
    • Groundwater Flowpaths (SIDE view) Flat Ground LocalRegional SpringSprings With Hills and Topography
    • unconfined aquifer• An unconfined aquifer is an aquifer that is bounded by a confining layer at its bottom but not at its top.
    • an unconfined aquifer
    • confined (or “artesian”) aquifer
    • Flowing “artesian” well
    • Catfish Farm WellFlowed 24,000 gpm July, 1991
    • catfish farm wellEdwards aquifer• flowing well at 40,000 gpm• 1/4 of San Antonio’s use• 9% of Annual Recharge• world’s largest artesian wellNational Geographic (1993)
    • confined or unconfined?
    • confined or unconfined?
    • same aquifer: unconfined and confined
    • Major aquifers
    • same location: confined and unconfined aquifers
    • Confined/Dipping Aquifer Warning: Not to Scale
    • Confined/Dipping Aquifer
    • Edwards
    • Gulf Coast
    • Carrizo-Wilcox
    • Carrizo Aquifer
    • Leaky Aquifers Water Table is Higher Semi-Confined water level is lower
    • Why do you care?Unconfined Confined
    • FLOW IN AQUIFERS
    • fundamentals
    • what is permeability? hydraulic conductivity ? transmissivity?• Terms that describe the ease with which water flows through geologic media.
    • What determines flow? Flow = KA dh / dl• Hydraulic properties• Water level variation• Aquifer geometry
    • Trinity cross-section 2400 A 2200 Edwards Group 2000 1800 Upper Trinity aquifer 1600 SE model boundary 1400 Guadalupe Middle Trinity aquifer River Canyon 1200 Lake 1000 No flow 800 No flow A’ 600 Recharge Groundwater flow Edwards aquifer Pumping (BFZ) 400 Drain Cross-formational flow Spring flow 200 Surface water-groundwater interaction 0 5 10 15 misea level
    • water flows down gradient(to lower potential energy)
    • PUMPING AN AQUIFER
    • pumping a well: unconfined
    • pumping a well: confined Aquifer may not be depleted Pressure is decreased
    • what is storativity?• Storage properties describe the amount of water released from an aquifer when water level drops• Confined : “storativity”• Unconfined : “specific yield”
    • Storage yields from aquifers• Unconfined aquifers 0.01 to 0.3• Confined aquifers 0.005 to 0.00005
    • Simple regional flow (sand)
    • Simple regional flow + well
    • Drawdown caused by well
    • Drawdown caused by well
    • Groundwater movement to well After 50 years
    • Groundwater movement to well After 100 years
    • MISCELLANEOUS IMPORTANTSTUFF
    • Miscellaneous• spring and stream impact• droughts and groundwater• long-term impacts• water quality
    • Springflow Impact Edwards AquiferHigh correlation
    • • Observed springflow increase following several wet winter months
    • Outcrop Well Pumping Well Middle Wilcox or Simsboro Aquifer OutcropPage 71
    • Outcrop and Downdip Hydrographs in Brazos and Robertson Counties Outcrop WellDepth to Water (feet) Pumping Well State Well Number, Screened Interval Page 72
    • Total water level declines in the major aquifers
    • Water level declines800600400 Paluxy200 Woodbine 0 Lower Trinity-200 1880 1920 1960 2000 Year
    • Depth to Water (feet) 400 350 300 250 200 150 100 50 0 Jan-45 Jan-47 Jan-49 Jan-51 Jan-53 Jan-55 Jan-57 Jan-59 Jan-61 Jan-63 Jan-65 Jan-67 Jan-69 Jan-71 Jan-73 Jan-75 Jan-77 Jan-79 Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95Static Water Levels in Carrizo Aquifer Wells (Angelina and Nacogdoches Counties) Jan-97 Jan-99 Water Levels in Carrizo Wells
    • Water Quality ~40,000 wells Deep saline units not included
    • Water Quality Edwards Aquifer
    • Drought Sensitivity - Major
    • Minor
    • Drought and Groundwater• Most aquifers are drought tolerant• Higher than usual water level declines in drought can be caused by increased pumping• Important to discern between local short- term and regional long-term impacts
    • Take Home1. Laws of physics are constant – however – geology, aquifers and groundwater can vary significantly over short distances2. Good science is critical for developing appropriate rules and management3. Good science takes time and money