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Lecture 9

ENSC 2001 Lecture Notes - Lecture 9: Surface Runoff, Water Table, Persistent Organic Pollutant

Environmental Science
Course Code
ENSC 2001
Quentin Gall

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ENSC 2001 A
Lecture 9
November 29th, 2015
Global Water Cycle
Cyclic nature:
1. Global movement of water between different water storage compartments
Global Distribution:
2. Abundance is not problem
3. Distribution in space and over time a problem
4. Supply vs. a problem
5. Humans are essentially competing for that 1% of water that is available
Table 12.1 The worlds water supply (pg 346)
1. Water exists in reservoirs as solid, liquid and gaseous form in the atmosphere over a period time
2. Water has different residents, and it is not always immediately available to use, not always in the
right form, or suitable for consumption
3. Water can spend thousands of years in the oceanic reservoir
4. Average residence time for water in the atmosphere is 9 days
5. Avg residence time for water in rivers and streams is 2 weeks
6. Groundwater shallow to depth of 0.8km, average residence time 1000 years
97% of water is located in oceans
2.15% of water is located in ice caps & glaciers
1% of water is freshwater
Potable water: Free of suspended matter, abiotic and generally mineral free. Referred to as fresh water.
USE of POTABLE WATER: 70% agriculture, 20% industry, 10% domestic use & drinking & recreation
Water has been divided into 2 categories:
1. Surface water
2. Ground water
Surface water: that which sits on the earths surface, exposed to the atmosphere and can be ingested or
absorbed into the earth to become groundwater.
1. Concerned with surface water since we reside on land
2. PEI, New Brunswick has more surface water but not all of it is potable (useable)
3. On land water flows over the surface from elevated lands to lower lands this is known as surface
runoff, this water tries to reach the ocean but ultimately gets caught up with rivers, streams and
4. Surface water erodes unconsolidated material as it moves across materials, therefore surface
water carries sediment
5. Surface water is referred to as drainage network
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Drainage basin or watershed: Separates two different divides of basin water.
Groundwater Profile:
1. Groundwater is water that infiltrates beneath the soil,
1. Groundwater moves downward to the vadose zone (unsaturated zone, zone of aceration)
2. Zone of saturation (accreation)
3. Moves down this area until its reaches the water table zone
Water table: The boundary of the above to zones between vadose zone and zone of saturation.
Hard Water: is water that has a high mineral content, formed when water percolates through deposits of
limestone and chalk (largely made up of calcium and magnesium carbonates).
Capillary Fringe: subsurface layer in which groundwater seeps up from a water table capillary action to
fill pores. Pores at the base of capillary fringe are filled with water due to tension and saturation.
Aquifer: Unit of capable of supplying ground water at useful rate (permeable, has hydraulic conductivity)
water can easily move through it.
Aquitard or aquiclude: A confining layer or unit restricting and retarding GW flow (impermeable) water
cannot move through it. Ex: clay rich materials, shale, un-fractured rock.
Unconfined Aquifer: No overlying confining layer above the aquifer that restricts the zone from
saturation. Nothing constraints it on the top.
Confined Aquifer: With an overlying aquitard layer. Something above the aquitard is constraining the
aquitard. Water tends to be under greater water pressure.
Artesian wells height decreases as you move away from the aquitard zone.
As you move away from water tower you get less and less pressure which decrease through a pressure
Perched Aquifer: Local zone of saturation above a regional water table.
Recharge Zone: Area where water is added to aquifer via natural process of human activity.
1. Groundwater tends to move very slowly
2. Tends to piles up in the recharge zone (clouds, precipitation, influent stream)
3. Groundwater can be higher in larger recharge areas
Influent Stream: Stream that loses water as it flows downstream. Water infiltrates into the ground
recharging the local groundwater, because the water table is below the bottom of the stream channel.
Cone of Depression: Extensive well pumping may cause the well water to enlarge; it will locally get
deflected towards that well.
Water quality decreases as you increase in depth; beneath the ground water becomes more saline.
Groundwater Use & Supply:
1. Damaging quality of groundwater is almost impossible to repair
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