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Ch.9. Erosion and Deposition. Section 3: The Force of Moving Water. Work and Energy Energy is the ability to do work or cause change Two kinds of energy: potential energy (is energy that is stored and waiting to be used later; Kinetic energy (is the energy an object has due to its motion

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Ch.9

Erosion and Deposition


Section 3 the force of moving water
Section 3: The Force of Moving Water

  • Work and Energy

    • Energy is the ability to do work or cause change

    • Two kinds of energy: potential energy (is energy that is stored and waiting to be used later; Kinetic energy (is the energy an object has due to its motion

    • As gravity pulls water down a slope, the water’s potential energy changes to kinetic energy that can do work

    • When energy does work, the energy is transferred from one object to another


Section 3 the force of moving water1
Section 3: The Force of Moving Water

  • How Water Erodes

    • Most sediment washes or falls into a fiver as a result of mass movement and runoff. Other sediment erodes from the bottom or sides of the river

    • Abrasion is another process by which a river obtains sediment

    • Abrasion is the wearing away of rock by a grinding action

    • Abrasion occurs when particles of sediment in flowing water bump into the streambed again and again; abrasion grinds down sediment particles

    • The amount of sediment that a river carries is its load

    • Gravity and the force of the moving water cause the sediment load to move downstream

    • Most large sediment falls to the bottom and moves by rolling and sliding

    • Fast—moving water actually lifts sand and other, smaller sediment and carries it downstream dissolving some sediments completely

    • The river carries these dissolved sediments in solution


Section 3 the force of moving water2
Section 3: The Force of Moving Water

  • Erosion and Sediment Load

    • A river’s slope, volume of flow, and the shape of its streamed all affect how fast the river flows and how much sediment it can erode

    • Slope

      • A river’s slope is the amount the river drops toward sea level over a given distance

      • If a river’s speed increases, its sediment load and power to erode may increase


Section 3 the force of moving water3
Section 3: The Force of Moving Water

  • Erosion and Sediment Load

    • Volume of Flow

      • A river’s flow is the volume of water that moves past a point on the river in a given time

      • During a flood, the increased volume of water helps the river to cut more deeply into its banks and bed

      • A flooding river can carry huge amounts of sand, soil, and other sediments


Section 3 the force of moving water4
Section 3: The Force of Moving Water

  • Erosion and Sediment Load

    • Streambed Shape

      • A streambed’s shape affects the amount of friction between the water and the streambed

      • Friction is the force that opposes the motion of one surface as it moves across another surface effecting the rivers speed

      • Where the river is deep: less water comes in contact with the streambed

      • Where the river is shallow: much of the water comes in contact with the streambed

      • Roughness thus increases friction and reduces the river’s speed.

      • Instead of moving downstream, the water moves every which way in a type of movement called trubulence


Section 3 the force of moving water5
Section 3: The Force of Moving Water

  • Erosion and Sediment Load

    • Factors Affecting Erosion and Deposition

      • Where a river flows in a straight line, the water flows faster near the center of the river than along its sides

      • If a river curves, the water moves fastest along the outside of the curve, there the river tends to cut into its banks, causing erosion

      • Sediment is deposited on the inside curve, where the water speed is slowest


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