Ch.9

1. Ch.9 Erosion and Deposition

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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