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Groundwater
water occurs in soil and rock
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GROUNDWATER BASICS
- A.POROSITY- storage capacity of rocks or sediment
- B.PERMEEABILITY-how fast water moves through rocks or sediments
- C.AQUITARDS(water closed)- impermeable rocks that prevent groundwater movement
- D. AQUIFIERS (water bearing)
- 1. Permeable rocks that store groundwater
- 2. Unconfined aquifiers
- a.Zone of aeration-layer in which pore spaces are filled with air
- b. Zone of satuaration- layer in which all pore spaces are filled with water
- c. Water table
- i. Tope of the zone saturation
- ii. Fluctuates during the year
- iii. Mimics overlying topography (ground surface)
- d. Unconfined aquifiers have an aquitard below but NOT above
- e. Water table wells are drilled into unconfined aquifiers
- i. When water is withdrawn from an unconfined aquifier, a cone of depression forms around well
- f. The Edwards Aquifier is unconfined in the recharge zone
- g. Perched water table
- i. Localized water table above the main water table
- ii.Form where there is an aquitar in the zone of aeration that traps water above the main water table
- 3. Confined aquifiers
- a. Have quitards both above and below the aquifier
- b. Artesian-pressure surface
- c.Artesian wells- water in the aquifier is under pressure and will rise to the level of the artesian pressure surface
- d. The Edwards Aquifer is conifined underneath SAC
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Springs and Geysers
- A. SPRINGS-form where the water table intersects the ground surface
- B.HOT SPRINGS-form where water is warmer than mean annual air temp
- C. GEYSERS-intermittent hot springs in which hot water errupts followed by stream
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Enviromental Problems
- A. MINING AND AQUIFER
- 1. Withdrawing groundwater faster than recharge occurs
- 2. High plains aquifer-North Texas to South Dakota
- B. GROUND SUBSIDIENCE
- 1.Water helps hold grains apart
- 2.Withdrawal of water allows grains to compact more closely
- 3.San Joaquin Valley
- a. Withdrawal of groundwater between 1925 and 1975 caused the ground surface to subside up to 28ft in places
- C. Groundwater pollution-sewage, chemical discharge, landfills. etc
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CAVES AND KARST TOPOGRAPHY
- A. MOST CAVES ARE FORMED AT OR SLIGHTLY BELOW THE WATER TABLE IN THE ZONE OF SATURATION IN LIMESTONES
- B. DEPOSITION OF THE TRAVERTINE OCCURS IN ZONE OF AERATION
- C.KARST TOPOGRAPHY
- 1. Surface features that form in humid areas underlain by limestone
- a. Sinkholes- form where the roof of cave collapses(slow or quick) leaving an opening at ground surface
- b. Disappearing streams-form where a stream flows into a sinkhole
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