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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
kinetic energy
load
friction
potential energy
abrasion
turbulence
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
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 movement and runoff.
Other sediment erodes from bottom 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.
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.
Erosion and Sediment Load
The power of a river to cause erosion and carry
sediment depends on several factors:
• Slope
• Volume
These all affect how fast the river flows
And how much sediment it can erode.
• 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.
Erosion and Sediment Load (Cont’d)
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.
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
_________.
Hoover Dam
How Hydroelectric
Power Works
(Click)
The Power of Water
(Click to see movie about
a renewable energy source.)
H2O
HHO (Click)
Last Night’s Homework – 9.3
The Force of Moving Water
Assessment:
1.a. What is energy?
It is the ability to do work or cause change.
b. How is a river’s potential energy changed into
kinetic energy? Gravity causes river water to move down
a slope. As the water flows, its potential energy
changes to kinetic energy.
c. What are two effects produced by flowing water
in a river? They are erosion and deposition.
2.a. What are the two main sources of sediment that
rivers and streams carry? The two sources are mass
movement and runoff.
Assessment (Cont’d)
2.b. Describe a process by which a stream can
erode its streambed. Sand and other sediment
grains can strike the rock of the stream’s bed and wear
it away. This process is abrasion.
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. The piece of rock will become
smaller and more rounded.
3.a. What 3 factors affect how fast a river flows?
Slope, volume of flow, and shape of the stream bed.
b. Study Fig. 17. Over time, what will happen to the
river’s bank at B? Why?
The river’s bank will eventually erode, and the curve
will become larger.