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Geography 12 CH10 Hydrological CycleV1.0 (KWP) Page 1 of 7

Chapter 10: Hydrological Cycle

The Water Cycle

The water cycle is a closed cascading system The water molecules circulate through the

system in a never ending cycleof renewal Water is the onlytruly renewable resourcein

that the same molecules circulating todayhave been with the earth since thebeginning

Looking at the journey a water moleculetakes through the system we can trace anysource of danger

The first challenge we face is in the availability of fresh water All life on the earth's surface requires fresh water to live However, there is a limited amount of fresh water for use The largest quantity of water is held in oceans This water has a high saline content and so is unavailable for human use and consumption

(salt water) The next largest store of water is the water held in glaciers and ice packs Because this water is not immediately available for use it is considered to be held in long

term storage The term cyclerefers to the fact that the water molecules flow through a series of events

which cause them to be used and reused for all life The water cycle is driven by the energy of the sun It begins with the evaporationof water from the ocean Water contains energy As it moves into the

atmosphere it createsweather and these weathersystems drive other systems

As it can be seen themovement of waterthrough the cycle carries

with it a lot of energy The water that flows from

the rivers and streams carryother elements to throughthe system as well

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The ocean

The oceans are the great storehouse of earths' water The oceans' great depths mean that the water takes a long time to recyclethrough the

system The convection currents in the ocean move the colder deep waters to the top but it does

take a long time It takes about a thousand years for deep ocean water to make its way to the surface where

it is recycled in the hydrological cycle The ocean is divided into two major zones These zones are distinguished by temperature and chemical composition The zones are separated by layer known as the Thermocline Thermo - to do with heat There is very little interchange between the zones due to the difference Under the thermocline is the deep ocean It is only recently, thanks to

satellite imagery, the we arelearning more about theocean floor

The deepest humans haveever dived was 10,900meters

That is the bottom of theMarian s trench The deepest part of the

earth's surface The Mariana's trench is

located off the coast of Japan It is the deepest part of the ocean

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The water in the oceans circulates This process keeps the clod ,nutrient

rich waters flowing to top where theycan feed the marine life

Since cold water is very dense, thewater off the Antarctic continent flows

into the ocean and down This generates a current which drives

the current known as the *AntarcticBottom water current* These deep water currents are essential

for the nutrient cycle of the ocean The other deep water current is the

one that is result of the North AtlanticDrift After the NAD has lost its heat energy, it falls

deep and continues the cycle south These deep water currents are responsible for

driving the oceans energy systems The oceans are comprised of deep trenches,

high mountains, large expanses known as Plains(see diagram below) The next great storehouse of water is found on

land Water frozen in ice sheets and glaciers is

considered long term storage Since salt water doesn't freeze, the water in

these ice sheets is freshwater It is unavailablefor human use however since its

properties are essential for maintaining thedelicate balance on earth

The salt that leaves the water contributes to thesalinity of the oceans

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Freshwater

Groundwater is all of the water foundbeneath the earth's surface

This includes vast caverns, contains or freshwaters called aquifers

This is our single most important source offresh water

We drill wells to tap into these storehouses Sometimes the aquifer has a part that is

close to the surface and the water seeps out This is an artesian well In the right-hand-side diagram you can see how

the water tableallows us access to the freshwaterbelow

Where the surface is below the water table youget a natural spring occur

Water in the water table is not always easilyaccessible Sometimes the depthis too great or there may be

a layer of hard rock material to prevent the easyexploitation of the water

Other times the water has been pollutedby industry or agriculture

Water gets into the aquifers through percolation As the water moves down through the soil, it is cleaned

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The replenishing of water in an aquiferis called recharge

This occurs when the moisture fromprecipitation of from snow melt seeps

into the ground

An aquifer can consist of a cap rockand a porous rock One of the easiest sources of freshwater is found in the rivers and lakes of the world Unfortunately heavy industrial demands have taken a great toll on this source of water Hard water versus soft water: Canadais home to more rivers and lakes than any other

country in the world except Russia and Brazil This makes it essential that we understand the value of this

resource - freshwater

A drainage basinis the area where all precipitation will draininto

Rivers have a drainage basin, thenthese rivers will drain into a lakecompleting its drainage basins thatexit in the ocean

In the 60s and 70s, the heavyindustrial around the Great Lakesled to serious environmentalconcerns

Lake Erieis the most shallow of allthe Great Lakes and yet was hometo a majority of industry

The pollutants poured into the lakewere causing severe environmentaldamage

By the late 70s, Lake Erie was dying The Lake Erie situation was a wake-up call

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Governments had to face some unpleasant realities The Canadian government began to take steps The Canadian government of the time passed a law requiring all industry to attach

"scrubbers" on the stacks Heavy pollutes dumped into the water must pass through settling ponds Eutrophication- water is very polluted and causes a massive amount of algae to grow,

killing marine organism

Atmosphere

The last great storehouse of freshwater is all around us The atmosphere has a vast amount of freshwater in its composition We refer to atmospheric moisture as humidity This was discussed in the last chapter. Water enters the atmosphere through the process of evaporation Important: when water changes state there is a release of energy

Precipitation occurs when water molecules form large enough to fall For this to happen, the water molecules need something to form upon These are called hygroscopic particles

Dry particles Wet particles Cloud particles (Not to Scale)

The ability for moisture to cling on to a hygroscopic particle has had to the science of cloudseeding

In areas of poor rainfall, farmers will sometimes hire people to seed the clouds

By putting hygroscopic particles of silver iodide into the atmosphere, clouds could beencouraged to create rain

RH100%

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Fog Two main types of fog Advection and radiation fog Fog, mist and cloud are all formed when air cools to its dew point Water in the air may condense onto a cold surface such as the ground, a house roof or on

to small particles in the air (known in the trade as condensation nuclei). At ground level the "cloud" is called fog or mistdepending upon the visibility Most common over land is Radiation Fog which occurs on a clear night with light winds Radiation from the ground escapes out to space, the ground cools and, in turn, cools the

air the air in contact with it. On an absolutely still night, condensation will occur on the ground to form dew This fog dissipates when a breeze blows in or the sun comes up Advection fogis the fog that is produced when damp air is moved across a surface that is

cooler than the air It is most commonly seen overseas or other bodies of water, but it is possible over snow-

covered or frosty land masses, as well.

When the temperature of the air is lowered to its dew point, changes start to happen In areas where sea air is cooled by the water, advection fogis most common Consequently, this fog is also called sea fog Advection fog is usually seen during certain seasons, specifically spring and the first few

months of summer At this time, the surface temperature of the sea water is either at its lowest temperature or

recovering from a winter season where it was already at its lowest.

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