EESA06H3 Chapter Notes - Chapter 15: Saline Water, Clay Minerals, Petrified Wood
10 May 2018
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Ch.15 – Groundwater
- Groundwater can form caves, sinkholes and petrified wood
- Can appear as hot springs and geysers
- Hot groundwater can produce geothermal energy
- 97.2 Ocean, 2.15 Glaciers and ice, .61 Groundwater, .009 Fresh Lakes, .008 Saline
Lakes, .005 Soil Moisture, .001 Atmosphere, .0001 Rivers
Groundwater: water that lies beneath the ground surface, filling pore space between
grains in bodies of sediment and classic sedimentary rock, and filling cracks and
crevices in all types of rocks
- 30% of Canada relies on groundwater for domestic use
- PEI relies on it completely
- Rain and snowfall source of groundwater
- Percolates into ground go become groundwater
- 15% of precipitation becomes groundwater
Porosity: percentage of rock or sediment that consists of voids or openings, is a
measure of a rock’s ability to hold water
Permeability: capacity of a rock to transmit a fluid such as water or petroleum
through pores and fractures
- A rock that holds much water is porous
- A rock that allows water to flow easily is permeable
- Sandstones and conglomerates are porous and permeable
- Impermeable rock is one that does not allow water to flow easily
- Unjointed granite and schist are impermeable
- Shale has porosity and low permeability
- Sedimentary pores tend to be closed with depth
- Caused by cement and weight of overlying rock
- Overlies igneous and metamorphic with low porosity
Saturated Zone: surface zone in which all rock openings are filled with water
- Used for wells
Water Table: upper surface of saturated zone marked by water level
- Rivers and lakes intersect saturated zone
Unsaturated Zone: above water table and is unsaturated
- Surface tension causes water to be held above water table
- Capillary Fringe is transition zone with higher moisture content at base of vadose
zone above water table
- Some water drawn or wicked upward from water table
- Less than a metre thick
- Plant roots obtain water from belt of soil moisture near top of saturated zone
- Fine-grained clay minerals hold water and make it available for plant growth
- Plants drown if roots are covered by water in saturated zone
- There are exceptions
Perched Water Table: top of a body of groundwater separated from main water
table beneath it by a zone that is not saturated
- Forms as groundwater collects above lens of less permeable shale within a more
permeable rock, like sandstone
- If intersects surface then can form line of springs along upper contact of shale lens
- Can act as short term water supply
- Determine shape and position of water table by mapping water levels in waterwells
and boreholes
- Analyze subsurface water movement, calculate flow rates and predict position of
water table if no boreholes
- Essential to find more groundwater sources
- Groundwater moves slowly through rock
- Moves in response to difference in water pressure and elevation
- Water in upper saturated zone moves downwards following water table slope
- Circulation of groundwater in saturated zone not confined to shallow layer beneath
water table
- Groundwater may go down deep before rising back
- May become a spring or seep into rivers and lakes
- Slope of water table strongly influences groundwater velocity
- Steeper slope, faster movement
- Slope controlled largely by topography
- Groundwater will not move if water table is flat
- Speed of flow also dependant on rock permeability
- Slow flow if small and poorly connected pores
- Fast if large and well connected pores
- Use dye as tracer of water flow speed
- Groundwater velocity varies widely
- Near impermeable rocks may let water move cm a year
- Highly permeable rocks, unconsolidated gravel and cavernous limestone, can allow
km a day
Aquifer: body of saturated rock or sediment through which water can move easily
- Highly permeable and saturated with water
- Wells must reach aquifer for adequate supply
- Good aquifers include sandstone, conglomerate, well-jointed limestone, bodies of
sand and gravel, and some fragmental or fractured volcanic rock such as columnar
basalt
- Sought in prospecting for groundwater or drill water wells
- In Canada aquifers are found in permeable gravel and sand and glacial tills
- Shale and clay are relatively impermeable
- Crystalline rocks such as granite, gabbro, schist and some limestones are not good
aquifers because not very porous
- Shale and crystalline rocks also called aquitards as slow down flow
- Highly fractured crystalline rocks can be dependable
Unconfined Aquifer (UA): has water table as only partly filled with water
- Recharged by precipitation
- Rising and falling water table during wet and dry seasons
- Rapid movement of ground water
- Susceptible to contamination
Confined Aquifer (CA): completely filled with water under pressure; separated from
surface by impermeable confining bed or aquitard
- Recharged slowly through confining shale or clay beds
- Slow groundwater movement
- Can have no response to wet and dry seasons
- Less contaminated source of drinking water
Well: a deep hole, generally cylindrical, that is dug or drilled into to ground to
penetrate an aquifer within the saturated zone
- Water must be lifted or pumper
- Water table falls during dry seasons as water flows out of saturated zone into springs
or rivers
- Wells must be deep enough to intersect lowered water table
Recharge: addition of new water to the saturated zone
- Rainy seasons return water to dry wells
Cone of Depressions: when water is pumped from a well, the water table is typically
drawn down around the well into a depression shaped like an inverted cone
Drawdown: local lowering of water table
- Tends to change direction of groundwater flow by changing the slope of the water
table
- Drawdown and cone of depression don’t occur in lightly used wells not pumped
- In UA, water rises in shallow wells to level of water table
Artesian Well: in CA, water is under pressure and rises in wells to level above top of
aquifer
- CA also called Artesian Aquifer
- Water can rise to surface in some artesian wells
- Produces flowing well that spouts continuously unless capped
Spring: water flows naturally from rock onto land surface
- Some discharge where water tables intersects land surface
- Occur where water flows out from caverns, fractures, faults or rock contacts that
come to surface
Document Summary
Groundwater can form caves, sinkholes and petrified wood. Can appear as hot springs and geysers. 97. 2 ocean, 2. 15 glaciers and ice, . 61 groundwater, . 009 fresh lakes, . 008 saline. Lakes, . 005 soil moisture, . 001 atmosphere, . 0001 rivers. Groundwater: water that lies beneath the ground surface, filling pore space between grains in bodies of sediment and classic sedimentary rock, and filling cracks and crevices in all types of rocks. 30% of canada relies on groundwater for domestic use. Porosity: percentage of rock or sediment that consists of voids or openings, is a measure of a rock"s ability to hold water. Permeability: capacity of a rock to transmit a fluid such as water or petroleum through pores and fractures. Impermeable rock is one that does not allow water to flow easily. A rock that holds much water is porous. A rock that allows water to flow easily is permeable. Sandstones and conglomerates are porous and permeable.
