Where in the world is the water??

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Where in the world is the water??

More than 97% of all Earth’s water is in the oceans.

Only <1 % of Earth’s water is available to us as water vapor, groundwater, and freshwater.


Earth’s waters are constantly circulating. The driving forces are:• Heat from the Sun • Force of gravity

The Hydrologic Cycle(Water Cycle)


Controls the circulation of water on Earth.Processes involved:

•Evaporation•Condensation •Precipitation•Infiltration•Runoff

The Hydrologic Cycle


The Hydrologic CycleWater makes a complete loop. The journey is not always direct.

•Can flow as groundwater•Can be frozen in ice caps and glaciers


The Hidden WaterGroundwater –Saturated zone—water has filled all pore

spaces.Unsaturated zone—pores filled with water

and air.

The water table is the boundary between these two zones.


Water TableThe depth varies with precipitation and climate.

• Zero in marshes and swamps, hundreds of meters in some deserts.

• At perennial lakes and streams; is above the land surface.

• Tends to rise and fall with the surface topography.


Storage and Movement of Groundwater

Factors:• Porosity: ratio of open space in soil,

sediment, or rock to total volume of solids —the amount of open space underground.• Greater porosity equals more

potential to store greater amounts of groundwater.• Particle size, shape, and sorting

influence porosity.Soil with rounded particles of similar

size has higher porosity than soil with various sizes.


Storage and Movement of Groundwater

Permeability•Degree to which groundwater can

flow through a porous material—higher permeability, greater potential for fluid flow.

• Influenced by sediment packing and connectedness of pores.

•Measured by hydraulic conductivity


Groundwater

Darcy’s law:

Groundwater flow rate = hydraulic conductivity cross-sectional area hydraulic gradient


Aquifers• Reservoirs of groundwater. • High porosity and high permeability.• Underlie the land surface in many areas; they are a

vital source of fresh water.It is important to keep this vital source of fresh water

clean and contaminant free.


A perched water table- discontinuous, low-permeability layers in

an unconfined aquifer trap water that is percolating downward.


The Work of Groundwater

Flowing groundwater can alter and change features at the surface:•Land subsidence•Caves and caverns•Sinkholes


Land Subsidence:• Extreme groundwater withdrawal

by pumping from wells can result in lowering of the land.

• Especially prevalent in areas underlain by sandy sediments and interbedded clays. The clays leak water to the sand, then when water is pumped out, the clays shrink and compact, causing subsidence.


Caverns and caves• The dissolving action of groundwater “eats

away” at rock—limestone in particular.•Rainwater chemically reacts with CO2 in

the air and soil, producing carbonic acid. • The acidified water seeps into rock partially

dissolving it.


Surface WaterRivers, lakes, reservoirs

Rivers sculpt and shape Earth’s surface:• Erosion—carves the landscape (fast

water)• Deposition—shapes the land as sediment

is deposited (slow water)


Surface Water

Stream channels in high mountain areas cut into underlying rock.

Fast-moving rapids and beautiful waterfalls are characteristic of V-shaped mountain stream valleys.


StreamflowLaminar flow—gentle, not impeded,

often fast

Turbulent flow—impeded, “White water” and often slower


Velocity factors•Gradient, or slope

•Channel characteristics (shape and size)

•Discharge—volume of water moving past a given point in a certain amount of time


Stream speed - usually not constant along the length of a stream.

• As stream moves downslope, gradient decreases and the channel widens.

• Discharge usually increases as tributaries add water.

Average stream speed=discharge/cross-section(River speeds never go more than 4-5 mph)

Velocity


The Work of Surface WaterStream erosion:

• Loosely consolidated particles are lifted• Hydraulic action• Abrasion

Stronger currents lift particles more effectively:•Stronger currents have “higher” energy•Lift and transport more and bigger particles•Turbulent flow most effective


Stream Sediment Load • Dissolved load- dissolved ions• Suspended load- clay-silt• Bed load- sand, gravel, pebbles, boulders


Speed varies within channel Slower along the stream bed Greater near the surface.

Maximum flow speed occurs mid-channel.


Erosion vs. DepositionStream speed plays a role • Fast water erodes the bank• Slower water deposits sediments


FloodplainMeandering streams create a wide belt of

almost flat land: a floodplain.When a flood occurs, sediment is deposited

in the floodplain. Large, coarse sediment creates natural levees.


Drainage basins and dividesDrainage Basin-the land area that contributes water to a stream.Drainage Divides- separate basins

The largest drainage divides are continental divides.


The Work of Surface Water

A delta is where a flowing stream meets a standing body of water. The flow slows down and the stream dumps sediment.

The result is a fan-shaped deposit of new land.


Glaciers and GlaciationAccumulation of snow and ice thick enough to move

under its own weight• Two types:

—Alpine —Continental


Glaciers and Glaciation

Alpine glaciers develop in mountainous areas, confined to individual valleys.

Cascades, Rockies, Andes, Himalayas

Continental glaciers cover broad expanses .

Antarctica and Greenland


When glacial ice melts, it drops a poorly sorted load of boulders, pebbles, sand, and clay.

Poor sorting is the hallmark that differentiates glacial sediment from material deposited by streams and winds.


Growing or RetreatingThe mass of a glacier changes over time. As snow falls, accumulation makes the glacier grow. As ice melts, sublimates, or breaks off, ablation

occurs.


The Work of WindWind blows everywhere, but its impact on sculpting the

land is minor.Impact is greatest where:

• Strong winds blow frequently• Vegetation is sparse or absent

—Plant roots keep particles together—Plants deflect wind and shelter particles

• Surface particles are small —Small particles are more easily lifted and transported

Where in the world is the water??

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