ENSC 2001 Lecture Notes - Lecture 9: Phreatic Zone, Sinkhole, Spinach
Course CodeENSC 2001
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Global water cycle
Global movement of water between different water storage compartments. Resident time can vary.
Cloud formation->raincloud->precipitation -> surface runoff -> ocean
Infiltration -> groundwater flow ->ocean
Evaporation from vegetation/land/ocean ->cloud
Abundance is not the problem. Inequality in distribution in space and over time is the problem.
Supply Vs Demand is another problem.
Global transfer of water
Evaporation from oceans to atmosphere, evaporation from lands to atmosphere
Precipitation to oceans, precipitation to land
Runoff of surface water and groundwater from land to oceans
(Cloud) transfer of water from atmosphere to land
97% of water exists in the ocean.
2% of water exists in form of ice caps and glaciers.
Only less than 1% of water is available in the right form and suitable for use
Potable Water (fresh water or drinking water)
Free of suspended matter, generally mineral free. The quantity of fresh water is critical to population.
Use of water:
70% agricultural, 20% industrial, 10% domestic use/drink and recreation
Developed country tend to use more water than developing country.
CA is high on use of water: 300 L per day per capita
Most CA provinces have more surface water than ground water.
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Drainage Basin: an area of land that contributes water to a particular stream or river. It is a basic unit of
the landscape. The flow of water on land is divided into watersheds or drainage basin.
Drainage divide: the boundary between the drainage basins.
Surface runoff: water runs cross the land from high to low, ultimately to reach sea level. But often it is
caught in lakes or rivers, it carries sediment and dissolve them into streams and eventually water. This
carriage is referred s drainage network
Ground Water (80% of fresh water)
Water moves downward through vadose zone. (Vadose zone: unsaturated zone, zone of aeration.) Then
it reaches zone of saturation (phreatic zone)
Water table: the boundary of the vadose zone and the phreatic zone.
Hard water: pick up element in vadose zone. Calcium-magnesium is dissolved in vadose zone.
Aquifer: a unit capable of supplying water at an economically useful rate (permeable, has hydraulic
conductivity). For example: sand, gravel, soil, and fracture rock, as well as granite and metamorphic
rocks with high porosity. So long water can easily move through it.
Aquitard: also called aquiclude. A confining layer or unit restricting and retarding GW flow
Confining layer: restricts or blocks the movement of GW, for example clay or shale layer
Unconfined aquifer: no overlying confining layer to restrict the upper surface of the zone of saturation
at the water table.
Confined aquifer: with an overlying aquitard layer
Perched aquifer: local zone of saturation above a reginal water table
Recharge zone: area where water is added to aquifer via natural process (precipitation, affluent surface
water) or human activity (water injection, bleach of a water pipe). (lack of snow and rain was the main
cause for the 2014 drought in US) (Groundwater moves slowly and gather beneath recharge and rise up
in area of recharge)
Groundwater discharge: remove GW from an aquifer. Example: spring (form when GW intersects with
the earth’s surface)
Cone of depression: forms in water table or artesian pressure surface. Over-pumping an aquifer cause
the water table to drop deeper within earth. The cone of depression forms around the well, lowering
the water table and lowering the pump settings or requiring drilling deeper wells. This could potentially
lead to degradation of water quality (more dissolves as deeper the water)
Consequences of dropping water table
o Surface subsidence can happen (sink hole)
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