Stages in the “Life-cycle” of a Stream

Cut out each diagram. Paste onto the description sheet in order and identify their characteristics by filling in the adjoining table.

Name______ES period___

Date______Mr. Landsman

Stream stages

Geologists characterize streams as youthful, mature, and old. Typically, streams have steep gradients near their sources, or beginnings, and gentle gradients as they approach their mouths, or ends. Discharge increases downstream as more tributaries connect with main streams as they flow toward their base levels. Because of this, stream channels also become deeper and wider downstream.

A youthful streamor UPPER COURSE has a fairly straight channel and a steep gradient. It generally flows in a V-shaped valley in a highland or mountainous area with little shifting of its channel. Its speed is high (turbulent, not linear), and it is actively lowering its channel through downcutting in order to reach base level. In this stage, a stream has little, if any, floodplain. Rapids and waterfalls may mark its course.

Category/Feature / Description
Gradient
Speed
Valley Shape
Erosion type / Downcutting
Floodplain

A stream in its mature stageor MIDDLE COURSE,has a moderate gradient and speed because it has eroded its bed downward and is closer to base level. Since it has slowed down, the stream begins to meander (bend). While it is still eroding downward, the stream's main force of erosion is lateral (horizontal) as it begins winding back and forth, carving out a valley floor between valley walls or bluffs. Periodically, the stream will flood all or a part of its valley, depositing alluvium on its developingfloodplain.

Category/Feature / Description
Gradient
Speed
Valley Shape
Erosion type/force
Flooding?
Meanders?
Oxbow Lakes?

An old age stream or LOWER COURSE has nearly reached its base level, and its gradient and speed are very low. Because its speed is low and less turbulent, it has lost its ability to erode downward. In fact, it deposits as much material as it erodes. The stream meanders greatly in its nearly flat valley. It has a wide, well-developed floodplain marked with oxbow lakes.

Category/Feature / Description
Gradient
Velocity
Valley Shape
Erosion AND Deposition
Flooding?
Meanders?
Oxbow Lakes?

Refer to the diagram above, your stream stages pages, and vocabularyto answer the following questions:

1. What type of erosion is responsible for the deep valley in the upper course (between 1 & 3)? ______

2. What type of erosion is responsible for the widening of the lower course valley (4-5) and development of meanders?

______

3. What location is likely to have distributaries? (1) (2) (3) (4) (5)

4. Why is widespread flooding more likely between 4 & 5 than between 1 & 2? Hint: look at the banks.

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