EARTHSC 1G03 Lecture Notes - Capillary Fringe, Aquifer, Gabbro
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15 – GROUND WATER
Ground water: fresh water beneath the ground surface, filling pore space b/c grains in bodies of
sediment and clastic sedimentary rock, and filling cracks/crevices; roughly 1% of water on Earth
Divided into 3 “zones” in the ground: unsaturated, water table, saturated zone
1. Unsaturated Zone: air and water fill pores collectively; surface tension causes water to be held
above water table
2. Water table: The line that divides the unsaturated and saturated zones – this is also the upper
limit of the saturated zone; capillary forces create a transition zone above the WT
3. Saturated Zone: water fills the pores of rocks/sediment
Source of groundwater is snow and rain which percolates down to the water table (~15%).
Position of the water table depends on seasonal factors - only water in the saturated zone is
Capillary fringe: transition zone where water is located higher than the water table due to
capillary effects. In rocks with smaller pore spaces (e.g. clay) we see a higher water level than
rocks with larger pore spaces (i.e. gravel).
Porosity: percentage of rock or sediment that consists of voids or opening for water to be held
High %: gravel, sand, silt, clay
Low %: glacial till, crystalline rock, shale
Permeability: capacity of a rock to transmit a fluid such as water or petroleum through pores or
Excellent: gravel, sand,
Poor: clay, glacial till, crystalline rock, shale, conglomerate
Aquifers: body of saturated rock that allows water to move through easily – conglomerate, well-
sorted little cement sand stone, well-jointed lime stone. Further subdivide into:
Unconfined aquifer: access to the surface and rainfall can percolate freely into the aquifer
o Quick recharge of water
Confined aquifer: bound by low permeability beds above and below, and can only get
water from surface exposure.
o Susceptible to pollution; slow recharge of water
Aquitard: rocks that do not allow water to transfer through it easily – shale, crystalline rocks
(gabbro, particular lime stone)
RECHARGING AND DISCHARGING
Recharge is the water goes into the saturated zone – typically upland; discharge is where the
water comes out of the surface – lakes, ponds, rivers. Groundwater generally moves from
recharge to discharge.
WATER FROM WELLS
Water wells are cylindrical holes dug or drilled into the ground penetrating an aquifer; must be
deeper to access water during dry season. Pumping results in the initially straight water table to
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