The Force of Moving Water

1. The Force of Moving Water (Click to see movie.)

2. 9.3 The Force of Moving Water • KEY CONCEPTS: • What enables water to do work? • How does sediment enter rivers and streams? • What factors affect a river’s ability to erode and carry • sediment? • KEY TERMS: • energy potential energy • kinetic energy abrasion • load friction turbulence

3. A river’s water has energy. Energy is? The ability to do work or cause change. potential __________ energy Potential energy is energy that is stored and waiting to be used later. kinetic _________ energy Kinetic energy is the energy an object has due to its motion. Merrimack River in NH and MA

4. How Water Erodes Gravity causes the movement of water across the Earth’s land surface. In the process of water erosion, water picks up and moves sediment. Sediment includes soil, rock, clay, and sand. How does sediment enter a river? Most sediment washes or falls into a river as a result of mass movementandrunoff. Other sediment erodes frombottom or sides of the river. Wind may also drop sediment into the water. Rivers also obtain sediment from abrasion. Abrasion is the wearing away of rock by a grinding action.

5. How Water Erodes (Cont’d) The amount of sediment that a river carries is its _____. load Gravity and the force of moving water cause the sediment load to move downstream. Large sediment falls to bottom and moves by rolling and sliding. Smaller sediment is lifted and carried downstream. Water dissolves some sediment Completely. The sediment carries these dissolved sediments in solution. *A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution. The most common solvent in everyday life is water.

6. Erosion and Sediment Load The power of a river to cause erosion and carry sediment depends on several factors: • Slope These all affect how fast the river flows And how much sediment it can erode. • Volume • Shape Slope is the amount the river drops toward sea level over a given distance. As more water flows through a river, its speed Increases.

7. Erosion and Sediment Load (Cont’d) A streambed’s shape affects the amount of friction between the water and the streambed. the force that opposes the motion of one surface as it moves across another. Friction is A deeper river with less water coming in contact with the streambed has less friction than a shallower river. A river full of boulders and other obstacles will have a lot of friction. This roughness increases friction and slows down the river. Instead of moving downsteam, the water moves every which way called _________. turbulence

8. Hoover Dam How Hydroelectric Power Works (Click)

9. The Power of Water (Click to see movie about a renewable energy source.) (Click) HHO H2O

11. Last Night’s Homework – 9.3The Force of Moving Water Assessment: 1.a. What is energy? b. How is a river’s potential energy changed into kinetic energy? c. What are two effects produced by flowing water in a river? 2.a. What are the two main sources of sediment that rivers and streams carry? It is the ability to do work or cause change. Gravity causes river water to move down a slope. As the water flows, its potential energy changes to kinetic energy. They are erosion and deposition. The two sources are mass movement and runoff.

12. Assessment (Cont’d) 2.b. Describe a process by which a stream can erode its streambed. c. Near a stream’s source, a stream erodes a piece of rock from its streambed. As the rock is carried down the stream, how will its size and shape change? Explain. 3.a. What 3 factors affect how fast a river flows? b. Study Fig. 17. Over time, what will happen to the river’s bank at B? Why? Sand and other sediment grains can strike the rock of the stream’s bed and wear it away. This process is abrasion. The piece of rock will become smaller and more rounded. Slope, volume of flow, and shape of the stream bed. The river’s bank will eventually erode, and the curve will become larger.