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 – 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 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 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 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 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 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