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

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 energykinetic energy abrasionload friction turbulence

Merrimack River in NH and MA

A river’s water has energy. Energy is?The ability to do work or cause change.

__________ energy

_________ energy

potential

kinetic

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.

How Water ErodesGravity causes the movement of water across theEarth’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 movement and runoff.

Other sediment erodes from bottom or sides of theriver.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.

How Water Erodes (Cont’d)

The amount of sediment that a river carries is its _____.loadGravity 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.

Erosion and Sediment Load

The power of a river to cause erosion and carrysediment depends on several factors:

• Slope

• Volume

• Shape

These all affect how fast the river flowsAnd how much sediment it can erode.

Slope is the amount the river drops toward sea levelover a given distance.

As more water flows through a river, its speed Increases.

Erosion and Sediment Load (Cont’d)

A streambed’s shape affects the amount of frictionbetween the water and the streambed.

Friction is the force that opposes the motion of one surface as it moves across another.

A deeper river with less water coming in contact withthe streambed has less friction than a shallower river.

A river full of boulders and other obstacles will have alot of friction. This roughness increases friction and slows down the river. Instead of moving downsteam,the water moves every which way called _________.turbulence

Hoover Dam How Hydroelectric

Power Works(Click)

The Power of Water

(Click to see movie abouta renewable energy source.)

H2O HHO (Click)

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.

The two sources are mass movement and runoff.

They are erosion and deposition.

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.