45:211: Environmental Geography ENVIRONMENTAL INTERRELATIONSHIPS Module 1.
45:211: Environmental Geography WATER Module 6. 45:211: Environmental Geography Water, water...
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Transcript of 45:211: Environmental Geography WATER Module 6. 45:211: Environmental Geography Water, water...
45:211: Environmental Geography
WATER
Module 6
45:211: Environmental Geography
Water, water everywhere
• Water is a vital resource for the biosphere and the human population.– The Same Water Has Been On This Planet
Since Time Began......
• However, quantitative supply and water quality issues are growing around the world.
45:211: Environmental Geography
Learning Objectives: Outline• Hydrologic Cycle
– Water supply– Storage reservoirs, recharge and discharge– Residence times
• Groundwater
• Water Use– In-stream; withdrawal; consumptive
• Water Pollution
45:211: Environmental Geography
Global Water
• 70% of earth’s surface is covered by water, although only a small fraction is readily usable by human beings.
Fresh Water = 3%Usable fresh water = .003% Most of the freshwater on Earth is in the form of permanent ice and snow, or groundwater.
45:211: Environmental Geography
Hydrologic Cycle
• All water is locked into a constant recycling process - the Hydrologic Cycle.– Solar energy evaporates water– Transpiration - Plants giving off water– Warm, moist air rises, cools water vapour
condenses and falls as precipitation.– Some precipitation remains on the surface and
evaporates, while most sinks into the soil and / or runs off into river systems and returns to the oceans.
45:211: Environmental Geography
Hydrologic Cycle
45:211: Environmental Geography
Hydrologic Cycle• In describing how water is cycled through the
hydrologic cycle, we will:– Know what is meant by recharge and discharge– Contrast the residence time of water in the Earth's
major reservoirs– Distinguish between the terms infiltration, runoff and
groundwater – Distinguish between the terms groundwater and
aquifer• Explain what is meant by groundwater mining
45:211: Environmental Geography
Recharge
• Some of the water from melting snow and from rainfall seeps into the soil and percolates into the saturated zone. This process is called recharge. – Places where recharge occurs are referred to as
recharge areas.
45:211: Environmental Geography
Discharge• Eventually, this groundwater reappears at the
ground surface. This is called discharge. – Groundwater may flow into streams, rivers,
marshes, lakes and oceans, or it may discharge in the form of springs and flowing wells.
• In addition, when precipitation falls on the land surface, some of the water runs off directly into lakes and rivers. This is also recorded as discharge.
45:211: Environmental Geography
Recharge and Discharge
45:211: Environmental Geography
Residence Times
• The reservoirs in the Hydrologic Cycle are renewed (through discharge and recharge) on a continual basis.
However, the rate at which renewal occurs differs with each reservoir.
45:211: Environmental Geography
Residence time of groundwater• The residence time of groundwater, i.e. the
length of time water spends in the groundwater portion of the hydrologic cycle, varies enormously. – Some water may spend as much as 10 000 or more
years underground.
• By comparison, the average turnover time of river water - the time it takes the water to completely replace itself, is about two weeks.
45:211: Environmental Geography
Reservoir Approximate ResidenceTime
Soil Moisture 0.2 yearsSeasonal Snow Cover 0.4 years
Glaciers 40 yearsGroundwater: Shallow Up to 200 years
Groundwater: Deep Up to 10,000 yearsLakes Up to 100 yearsRivers 0.05 years
Residence time for various natural reservoirs
45:211: Environmental Geography
Residence time and water quality
• A stable and highly soluble pollutant is dumped into a lake at the rate of 0.16 tonnes/day. – The lake volume is 4 x 107 m3, and – the average water flow-through rate is 8 x 104
m3/day.
• What steady-state concentration will the pollutant reach?
45:211: Environmental Geography
Calculating Residence Time
Residence Time = Volume of Lake (m3)
Rate of Throughflow (m3/day)
= 4 x 107 m3
8 x 104 m3/day
= 500 days
45:211: Environmental Geography
Calculating Pollution Level
• Dumping rate = 0.16 tonnes/day
• Therefore, in 500 days, (500x0.16) tonnes of pollutant will accumulate in the lake (i.e. 80 tonnes).
• This much pollutant is dissolved in the lake, which has a volume of 4 x 107 m3. The mass of water in the lake = 4 x 107 m3 x 1 tonne/m3
= 4 x 107 tonnes
45:211: Environmental Geography
The End Result
• The concentration of the pollutant in the lake will thus be = 80 tonnes
4 x 107 tonnes
= 2 parts per million (ppm)– If there was a safe limit of 1 ppm, the dumping
rate of the pollutant would have to be halved.
– If the throughflow rate was only 4x104 m3/day, the concentration would rise to 4 ppm.
45:211: Environmental Geography
Points to Ponder
• The size of the reservoir and the rate of water exchange determine the residence time of the water.
• The steady concentration of a pollutant is determined by the dumping rate and the residence time in the reservoir.
45:211: Environmental Geography
Reservoir Approximate ResidenceTime
Soil Moisture 0.2 yearsSeasonal Snow Cover 0.4 years
Glaciers 40 yearsGroundwater: Shallow Up to 200 years
Groundwater: Deep Up to 10,000 yearsLakes Up to 100 yearsRivers 0.05 years
Residence time for various reservoirs
45:211: Environmental Geography
Infiltration
• Most rainfall (or snowmelt) will either enter the soil (infiltration) or flow downhill over the surface (runoff).– Some of the water that infiltrates the ground
will be used by growing plants; and some of it will be stored for long periods in natural underground reservoirs as groundwater.
45:211: Environmental Geography
Runoff
• Water that remains on the surface and flows downhill until it enters a river system is called (surface) runoff. Sometimes this produces floods.
• The runoff ratio is defined as Runoff
Precipitation
• The flow of water in a river channel is called the discharge (m3/sec)
45:211: Environmental Geography
River Flows• The volume of water flowing in a river together
with the speed and timing of the flows determines how a river shapes the surrounding landscape and how people can use its waters. – Rainfall, snowmelt, and groundwater all contribute
to the volume of flow, producing variations from season to season and year to year.
– Dams may be used to regulate flows
45:211: Environmental Geography
Floods• In Canada, most high flows are caused by
snowmelt and occur in spring. This is the season when floods are most likely to occur.– The lowest flows on rivers in Canada generally occur
in late summer, when precipitation is low and evaporation is high, and in late winter, when precipitation is stored as ice and snow.
• The effects of high flows can be much less severe on rivers with large drainage basins (large storage capacity).
45:211: Environmental Geography
Floodplains
What is the return interval of floods of different magnitude?
45:211: Environmental Geography
Groundwater• Beneath the surface of the earth is a huge
reservoir of fresh water - groundwater.– Groundwater does not rest; it moves continuously,
but at a slow rate. Its speed is measured in m/day, and even per year.
(Surface water velocities are measured in m/sec)
• Wells intercept some groundwater but most of it continues until it reappears naturally in a spring or a seepage area and joins a watercourse.
45:211: Environmental Geography
Recharge and discharge
45:211: Environmental Geography
Importance of groundwater
• Groundwater contributes to water supply by: – Feeding streams, producing the entire flow of
some streams during dry periods – Replenishing wells, a valuable source of supply
for individuals, communities, industries, and farms
– Supporting important ecological systems such as wetlands
45:211: Environmental Geography
Aquifers
• Although groundwater exists everywhere under the ground, some parts of the saturated zone contain more water than others. – An aquifer is an underground formation of
permeable rock or loose material which can produce useful quantities of water when tapped by a well.
45:211: Environmental Geography
Aquifers• Unconfined Aquifer - Usually near the earth
surface. The lower boundary is an impermeable layer of clay or rock. Water is at atmospheric pressure and is recharged by rainfall and percolation.
• Confined Aquifer - (Artesian) Bounded on top and bottom by an impermeable layer - water is stored under high (overburden) pressure.
45:211: Environmental Geography
Groundwater Aquifers
45:211: Environmental Geography
Porous media
• Most of the aquifers of importance to humans are unconsolidated porous materials such as sand and gravel which are also permeable.– Clay has many spaces between its grains, but the spaces
are not large enough to permit free movement of water.
45:211: Environmental Geography
Groundwater Mining
• Around 2 billion people rely on groundwater as their only source of drinking water.
• Mining of groundwater refers to removal from an aquifer faster than it is replenished by the natural processes of recharge. – Extended periods of groundwater mining can lead
to land subsidence, lowering of the water table, and even salt-water intrusion of wells in coastal areas.
45:211: Environmental Geography
Water Use: Objectives
• Know what is meant by withdrawal and consumptive uses of water
• Summarize the four main categories of water use– domestic, agricultural, industrial, in-stream – list the main in-stream uses of water
45:211: Environmental Geography
In-Stream Uses of Water
• Major in-stream uses are hydroelectric power, recreation, and navigation.
• The United States, for example, has nearly 5,500 large dams and over 100,000 small ones.– Dams are barriers to migrating fish and to the
natural movement of sediments, nutrients, and water
45:211: Environmental Geography
Hydro power in Canada• 60% of the total power generated in Canada
comes from hydro sources:– over 85% in Manitoba, Quebec, Newfoundland and
Labrador, British Columbia, and the Yukon, – 9.4% for Nova Scotia, 4.2% for Alberta, and 0% for
Prince Edward Island.
• In 1995, the United Nations ranked Canada as the world's largest hydroelectric producer, with 14% of the global output.
45:211: Environmental Geography
Other Water Use
• Water Withdrawal - withdrawing water and then returning it to its original source (but likely changed in quality).
• Water Consumption - withdrawing water and incorporating it into a product, or otherwise moving it to another area so it does not make it back to its original source in the hydrologic cycle.
45:211: Environmental Geography
Sectoral Water Use in Canada
Thermal Power Generation
63%
Mining1%
Manufacturing16%
Agriculture9%
Municipal/Domesic
11%
45:211: Environmental Geography
Domestic Water Use
• Relatively small amount (~10%) of global freshwater is withdrawn for municipal and domestic uses.
• Most of the water used for domestic purposes is returned to rivers as wastewater.
• Natural purification processes cannot cope with highly concentrated wastes typical of large urban areas.
45:211: Environmental Geography
• Domestic water is “wasted” rather than consumed.
• Public attitude:– Wherever water is considered limitless and
inexpensive, little effort is made to conserve it.
45:211: Environmental Geography
Agricultural Use
• The major consumptive use of water in most parts of the world is agriculture - for irrigation, where water is evaporated into the atmosphere.– In extreme cases, significant disruption to
natural systems can occur (see next slide)
• Increasing water costs will stimulate conservation - e.g. trickle irrigation
45:211: Environmental Geography
The Aral Sea - no more• Since 1960, this massive lake (once the world’s
fourth largest) has lost 75% of its volume. – Today, 94 percent of the river flow that once fed the Aral
Sea is diverted to irrigate cash crops such as cotton in this arid region.
– The sea's salinity levels have tripled and 20 of its 24 fish species have disappeared.
– The fish catch, which once measured 44,000 tons and supported 60,000 jobs, is now nonexistent.
– Over 36,000 square kilometers of former lake bottom are dry and bare.
45:211: Environmental Geography
Industrial Use of Water
• 90% of water used by industry is for cooling, and is returned to the source (withdrawal). – Most industrial processes involve heat exchange.– Very little water is actually consumed but it is
changed in quality.
• Industry also uses water to dissipate and transport waste materials.– Stream and lake degradation
45:211: Environmental Geography
Water Pollution
• Explain what is meant by water pollution– Give an example of water pollution from
municipal, agricultural and industrial use of water
• Explain what is meant by thermal pollution of water
• List the five major sources of groundwater pollution
45:211: Environmental Geography
Water Pollution
• Water pollution occurs when the use of water by one segment of the population interferes with the health and well-being of others (and ecosystems).– Water Pollution usually applies to changes in
the quality of water, although changes in the quantity (supply) can also interfere with health and well-being.
45:211: Environmental Geography
Domestic Water Pollution
• Waste from homes consists primarily of organic matter from garbage, food production, and human waste.– Coliform bacteria - generic term for bacteria
found in human intestines.– Numbers and types of bacteria present are
directly related to amount of human waste entering system.
45:211: Environmental Geography
Industrial Water Pollution
• Thermal Pollution - occurs when water is withdrawn and used for cooling purposes, and then heated water is returned to its original source in the environment.– An increase in temperature, even a few degrees,
may significantly alter some aquatic ecosystems.
45:211: Environmental Geography
Sources of Groundwater Pollution• Agricultural products - pesticide contamination• Underground storage tanks - gasoline and chemical
products can leak out.• Landfills - leachate (prevent infiltration)• Septic tanks - insufficiently treated domestic wastes• Surface impoundments - pits, ponds and lagoons
used to store and treat wastes; may be insufficiently lined or isolated from groundwater (use impermeable lining).
45:211: Environmental Geography
Water Use Planning Issues• Wastewater Treatment - see text.
– Quality of water must be appropriate to intended use, including pre-consumption treatment and post-consumption treatment for return to the ecosystem.
• Water Diversion– Physical process of transferring water from one
area to another; transboundary issues– Extensive draining can lead to wetland drainage
and habitat loss
45:211: Environmental Geography
Trans-Boundary Water
45:211: Environmental Geography
Summary• Hydrologic cycle driven by sun’s energy
– infiltration, runoff, recharge, discharge– residence times
• Groundwater– aquifers, mining
45:211: Environmental Geography
Summary
• Four human uses of water– Domestic In-stream– Agricultural Industrial
• Major sources of water pollution are municipal sewage, industrial waste, and agricultural run-off– Thermal pollution can cause habitat change