World GeographyWorld Geography

Unit 1: Physical GeographyUnit 1: Physical Geography

Land and Water FormsLand and Water FormsRunning Water, Erosion and DepositionRunning Water, Erosion and Deposition

The Growth of RiversThe Growth of Rivers When land can no longer absorb water it When land can no longer absorb water it

collects on the surfacecollects on the surface This gathers together on the land and This gathers together on the land and

begins to flow along the groundbegins to flow along the ground As more water gathers together it can be As more water gathers together it can be

defined by different terms.defined by different terms. Rivulets -> Streams -> RiversRivulets -> Streams -> Rivers The area of land that a river drains is The area of land that a river drains is

known as a known as a Drainage BasinDrainage Basin Drainage basins are divided by high parts Drainage basins are divided by high parts

of land known as of land known as Divides Divides

RivuletsRivulets

Small and Large StreamsSmall and Large Streams

RiversRivers

Drainage BasinDrainage Basin

River Life CyclesRiver Life Cycles

The characteristics of a river change The characteristics of a river change over timeover time

We refer to these changes as the We refer to these changes as the rivers lifecyclerivers lifecycle

There are three phases in the There are three phases in the lifecycle of a riverlifecycle of a river• YouthfulYouthful• MatureMature• OldOld

Life Cycles of RiversLife Cycles of Rivers

Youthful Rivers:Youthful Rivers:• Steep slopeSteep slope• Fast flowingFast flowing• RapidsRapids• Few tributariesFew tributaries• Cuts deep into the bed rather than wide Cuts deep into the bed rather than wide

into the banksinto the banks• Narrow V-shaped valleyNarrow V-shaped valley

Life Cycles of RiversLife Cycles of Rivers

Mature Rivers:Mature Rivers:• Less steep and slower than youthful Less steep and slower than youthful

rivers.rivers.• Many tributaries, and large discharge.Many tributaries, and large discharge.• Cuts a wider bed than youthful riversCuts a wider bed than youthful rivers• Well developed flood plain.Well developed flood plain.• Erosion is nearly equal to deposition Erosion is nearly equal to deposition

thus the river is in a state of equilibriumthus the river is in a state of equilibrium

The Life Cycle of RiversThe Life Cycle of Rivers

Old RiversOld Rivers• Slow flowing.Slow flowing.• Low gradient.Low gradient.• Large flood plain.Large flood plain.• Elaborate meandering (bending) Elaborate meandering (bending)

system.system.• Muddy appearance due to low sediment Muddy appearance due to low sediment

load.load.

Life Cycle of a RiverLife Cycle of a River

How to tell how old a river is?How to tell how old a river is?

SteepnessSteepness Number of tributariesNumber of tributaries DischargeDischarge Shape of river bedShape of river bed Flood planesFlood planes Amount of debris in waterAmount of debris in water

Erosion By WaterErosion By Water

Water Erosion occurs in two main Water Erosion occurs in two main waysways• Vertical ErosionVertical Erosion

The downward erosion into the riverbedThe downward erosion into the riverbed

• Lateral ErosionLateral Erosion The outward erosion of, widening it’s banksThe outward erosion of, widening it’s banks

Erosion by WaterErosion by Water

Vertical Erosion (4 Types)Vertical Erosion (4 Types)• Hydraulic Pressure: The weight of the water in Hydraulic Pressure: The weight of the water in

a river pushes against loose material moving it a river pushes against loose material moving it to a new positionto a new position

• Solution/Corrosion: The disolving of material Solution/Corrosion: The disolving of material into the river as the water passes over them.into the river as the water passes over them.

• Abrasion: Small particles flowing through the Abrasion: Small particles flowing through the river bump and scratch against other material river bump and scratch against other material gouging and grinding as the water flows.gouging and grinding as the water flows.

Erosion by WaterErosion by Water

Lateral Erosion:Lateral Erosion:• As rivers age they loose their steep As rivers age they loose their steep

slopes and begin to cut away at their slopes and begin to cut away at their banksbanks

• These rivers take on meandering shapesThese rivers take on meandering shapes• Faster water traveling on the outside of Faster water traveling on the outside of

the turns cuts into the bankthe turns cuts into the bank• Slower moving water on the inside of Slower moving water on the inside of

meanders deposits sediment.meanders deposits sediment.

Where does the Sediment go?Where does the Sediment go?

Fast flowing water can hold a lot of Fast flowing water can hold a lot of sediment.sediment.

As water slows it looses energy, and has to As water slows it looses energy, and has to drop some of its sediment load.drop some of its sediment load.

At the mouth of a river is one area where a At the mouth of a river is one area where a river slows, often leaving large deposits of river slows, often leaving large deposits of material.material.

These large deposits of material at the These large deposits of material at the mouths of rivers are known as deltas.mouths of rivers are known as deltas.

DeltasDeltas

Delta:Delta:• a landform that is created at the mouth a landform that is created at the mouth

of a river. They are formed by the of a river. They are formed by the deposition of the sediment carried by deposition of the sediment carried by the river as the flow leaves the mouth of the river as the flow leaves the mouth of the river. the river.

There are three main types of deltasThere are three main types of deltas• Arcuate deltaArcuate delta• Digitate deltaDigitate delta• Esturaine deltaEsturaine delta

DeltasDeltas

Arcuate Delta: A bowed or curved Arcuate Delta: A bowed or curved delta with a convex margin facing delta with a convex margin facing the body of waterthe body of water

DeltasDeltas

Digitate Deltas: Finger like, or bird Digitate Deltas: Finger like, or bird foot like deltas that form at the foot like deltas that form at the mouth of a rivermouth of a river

DeltasDeltas

Estuarine deltas: A delta formed in Estuarine deltas: A delta formed in that area of a river mouth which is that area of a river mouth which is affected by sea tides. Often taking a affected by sea tides. Often taking a convex shapeconvex shape