45:211: Environmental Geography WATER Module 6. 45:211: Environmental Geography Water, water everywhere Water is a vital resource for the biosphere and

45:211: Environmental Geography

WATER

Module 6


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.


Learning Objectives: Outline• Hydrologic Cycle

– Water supply– Storage reservoirs, recharge and discharge– Residence times

• Groundwater

• Water Use– In-stream; withdrawal; consumptive

• Water Pollution


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.


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.


Hydrologic Cycle


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


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.


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.


Recharge and Discharge


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.


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.


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


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?


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


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


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.


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.


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


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.


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)


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


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).


Floodplains

What is the return interval of floods of different magnitude?


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.


Recharge and discharge


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


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.


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.


Groundwater Aquifers


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.


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.


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


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


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.


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.


Sectoral Water Use in Canada

Thermal Power Generation

63%

Mining1%

Manufacturing16%

Agriculture9%

Municipal/Domesic

11%


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.


• Domestic water is “wasted” rather than consumed.

• Public attitude:– Wherever water is considered limitless and

inexpensive, little effort is made to conserve it.


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


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.


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


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


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.


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.


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.


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).


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


Trans-Boundary Water


Summary• Hydrologic cycle driven by sun’s energy

– infiltration, runoff, recharge, discharge– residence times

• Groundwater– aquifers, mining


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

Documents

45:211: Environmental Geography WATER Module 6. 45:211: Environmental Geography Water, water everywhere Water is a vital resource for the biosphere and