World Geography Unit 1: Physical Geography Land and Water Forms Running Water, Erosion and Deposition

The Growth of Rivers When land can no longer absorb water it collects on the surface When land can no longer absorb water it collects on the surface This gathers together on the land and begins to flow along the ground This gathers together on the land and begins to flow along the ground As more water gathers together it can be defined by different terms. As more water gathers together it can be defined by different terms. Rivulets -> Streams -> Rivers Rivulets -> Streams -> Rivers The area of land that a river drains is known as a Drainage Basin The area of land that a river drains is known as a Drainage Basin Drainage basins are divided by high parts of land known as Divides Drainage basins are divided by high parts of land known as Divides

Rivulets

Small and Large Streams

Rivers

Drainage Basin

River Life Cycles The characteristics of a river change over time The characteristics of a river change over time We refer to these changes as the rivers lifecycle We refer to these changes as the rivers lifecycle There are three phases in the lifecycle of a river There are three phases in the lifecycle of a river YouthfulYouthful MatureMature OldOld

Life 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 into the banksCuts deep into the bed rather than wide into the banks Narrow V-shaped valleyNarrow V-shaped valley

Life Cycles of Rivers Mature Rivers: Mature Rivers: Less steep and slower than youthful rivers.Less steep and slower than youthful 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 thus the river is in a state of equilibriumErosion is nearly equal to deposition thus the river is in a state of equilibrium

The Life Cycle of Rivers Old Rivers Old Rivers Slow flowing.Slow flowing. Low gradient.Low gradient. Large flood plain.Large flood plain. Elaborate meandering (bending) system.Elaborate meandering (bending) system. Muddy appearance due to low sediment load.Muddy appearance due to low sediment load.

Life Cycle of a River

How to tell how old a river is? Steepness Steepness Number of tributaries Number of tributaries Discharge Discharge Shape of river bed Shape of river bed Flood planes Flood planes Amount of debris in water Amount of debris in water

Erosion By Water Water Erosion occurs in two main ways Water Erosion occurs in two main ways Vertical ErosionVertical Erosion The downward erosion into the riverbed The downward erosion into the riverbed Lateral ErosionLateral Erosion The outward erosion of, widening it’s banks The outward erosion of, widening it’s banks

Erosion by Water Vertical Erosion (4 Types) Vertical Erosion (4 Types) Hydraulic Pressure: The weight of the water in a river pushes against loose material moving it to a new positionHydraulic Pressure: The weight of the water in a river pushes against loose material moving it to a new position Solution/Corrosion: The disolving of material into the river as the water passes over them.Solution/Corrosion: The disolving of material into the river as the water passes over them. Abrasion: Small particles flowing through the river bump and scratch against other material gouging and grinding as the water flows.Abrasion: Small particles flowing through the river bump and scratch against other material gouging and grinding as the water flows.

Erosion by Water Lateral Erosion: Lateral Erosion: As rivers age they loose their steep slopes and begin to cut away at their banksAs rivers age they loose their steep slopes and begin to cut away at their banks These rivers take on meandering shapesThese rivers take on meandering shapes Faster water traveling on the outside of the turns cuts into the bankFaster water traveling on the outside of the turns cuts into the bank Slower moving water on the inside of meanders deposits sediment.Slower moving water on the inside of meanders deposits sediment.

Where does the Sediment go? Fast flowing water can hold a lot of sediment. Fast flowing water can hold a lot of sediment. As water slows it looses energy, and has to drop some of its sediment load. As water slows it looses energy, and has to drop some of its sediment load. At the mouth of a river is one area where a river slows, often leaving large deposits of material. At the mouth of a river is one area where a river slows, often leaving large deposits of material. These large deposits of material at the mouths of rivers are known as deltas. These large deposits of material at the mouths of rivers are known as deltas.

Deltas Delta: Delta: a landform that is created at the mouth of a river. They are formed by the deposition of the sediment carried by the river as the flow leaves the mouth of the river.a landform that is created at the mouth of a river. They are formed by the deposition of the sediment carried by the river as the flow leaves the mouth of the river. There are three main types of deltas There are three main types of deltas Arcuate deltaArcuate delta Digitate deltaDigitate delta Esturaine deltaEsturaine delta

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

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

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