Chapter 6 Section 1 – Running Water
Water Cycle
• moves water between the oceans, atmosphere and land
• replenishes freshwater supplies
Infiltration – water on the surface of the Earth
moves down through cracks in the rocks or spaces
between the rocks
Transpiration – plants absorb water in the soil
through their roots and release it from their leaves
into the atmosphere.
• sometimes called
evapotranspiration
• 10% of the moisture in the
atmosphere
• large Oak tree can transpire
40,000 gal / year
• 1 acre of corn 3,000 – 4,000
gal/day
Streamflow – how water moves through a stream
Velocity – speed of the moving water
Things that affect velocity of water
•gradient – slope of the stream
• shape of the channel
• size of the channel
• roughness of its channel
• discharge – volume of water flowing past a
specific point in a given period of time
Headwaters – where a river begins
Mouth – where the river empties
Tributary – one stream that empties into another
Base Level – the lowest level the stream can
erode to; For streams that empty into the oceans,
base level is sea level. Local base levels occur
where a stream meets rock that doesn’t erode or
empties into a lake.
Meanders – a stream with many bends;
caused by being in a flat-bottomed valley near
the base level
1. Look at Figure 1 on
page 158
a. What percentage of Earth’s
water is not held in it’s oceans?
2.8%
b. Where is most of the Earth’s
freshwater located?
Glaciers
c. Where is most of the Earth’s
usable freshwater located?
Groundwater
2. Look at Figure 2 on p 159. Describe the three ways
precipitation returns to the oceans.
- rain or snow falls into the ocean
- water infiltrates into the ground and flows downhill
as groundwater until it reaches the ocean
- water runs off the surface and flows by rivers and
streams until it reaches the ocean
3. Look at Figure 3 on page 160. Explain how velocity
changes with depth in the middle of a stream.
Maximum velocity is in the center of a stream.
The velocity of the water decreases with depth.
4. Describe the factors that determine the velocity
of a stream.
a. gradient (steepness) of the stream - the
steeper the stream the faster the water flows
b. Discharge (how much water comes out) of the
stream – the more discharge the wider and
deeper the channel therefore the water flows
faster
c. Shape and size of the channel – deeper is faster;
shallower is slower
5. Explain what a stream profile is
A stream profile is a cross-section view of a
stream from its headwaters to its mouth.
6. Draw a picture of the water cycle
7. Explain how the Earth’s water cycle is balanced
The average annual precipitation over the Earth
equals the amount of water that evaporates.
8. What part does infiltration play in the water cycle?
Water that infiltrates the ground flows until it
reaches the ocean. Another way for water to return to
the ocean.
9. What factor most influences the power of a stream
to erode and transport material?
The stream’s velocity has the most influence on the
power of the stream to erode and transport
material.
10. How do gradient and discharge change between a
stream’s headwaters and its mouth?
Gradient decreases between a stream’s headwaters
and mouth. As more tributaries enter the stream
the discharge increases.
11. How might lowering base level affect stream erosion?
The vertical distance between the source and the base
level would increase. This would cause in an increase in
the velocity of the water and increased erosion. The
result would be to down cut the channel.
12. What would happen if evaporation exceeded
precipitation over the continents and oceans?
The Earth’s surface and oceans would start to dry up.
13. How does the development of urban areas
along streams and rivers affect discharge during
periods of heavy rainfall?
Construction of roads and buildings decreases
the amount of water the ground will absorb. This
increases and runoff - increasing the magnitude
and frequency of floods.
14. A stream that is 27 kilometers long drops 90
meters in elevation from its headwaters to its
mouth. What is the stream’s gradient? SHOW
YOUR WORK.