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 canerode 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 158a. 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 balancedThe 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.