Earth and Space Science / Unit 6: Water on Earth and the Oceans
6.3 Rivers and Streams
Notes
- A watershed (drainage basin) is the land area that drains to a river. A divide separates watersheds.
- Gradient is the slope of a stream: $\displaystyle \text{gradient} = \frac{\text{drop in elevation}}{\text{distance}}$. A stream dropping 300 m over 60 km has a gradient of 5 m/km.
- Steep streams cut deep V-shaped valleys; mature rivers meander on floodplains, eroding the outside of bends and depositing on the inside.
- Discharge $= \text{width} \times \text{depth} \times \text{velocity}$ (volume per second).
- Floods occur when discharge exceeds channel capacity.
Practice
A river drops 450 m over 90 km. Its gradient is:
$450 \div 90 = 5$ m/km.
A river's channel is 20 m wide and 2 m deep and water moves at 1.5 m/s. The discharge is:
$20 \times 2 \times 1.5 = 60$ m³/s.
On a meander, erosion is greatest on the:
Faster water on the outside undercuts the bank.
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