Week 29 - Water Affects Landforms and Climate on the Earth

Lesson 5

Lesson 5: Water Shapes Land
When water moves, in the form of rivers streams and rain, it erodes and changes the land. Sometimes the water slowly wears away the soil and the change in the land is very slow, but sometimes the water flows quick and more forcefully and the change is very fast.

Run-off is the water that flows through and along the ground vegetation and soil surface after a heavy rain. It can also erode the soil and remove valuable topsoil from the land thereby affecting streams, rivers and lakes that are part of the watershed.

Read the following and answer the questions below.

In an experiment to investigate what happens to run-off, a group of students set up three identical pans tilted at the same angle, Each pan had material attached to it. One had sponges attached to the surface, the other had paper towels attached and the third one had a plastic table cloth attached. (See the diagram below)

Initial volume of water
The water from the cylinder is poured at the top of the pan and then collected at the bottom
Pan with sponges
Pan with paper towel
Pan with plastic
Final volume of water collected



The most water flowed from the pan with plastic and the least run-off was from the pan with the sponges. In reality, a forested area would be represented by the pan with the sponges whereas the plastic surface would represents a parking lot or paved street. A forested area would have less run-off then a parking lot or paved street because water is absorbed into the soil of a grassy field or a forest and is used by the roots for plants to grow..

A relationship can also be made between run-off and pollution- The paper towels in B could represent an area of the forest that has been logged by a company. When an area has been logged most of the trees have been removed, leaving only small shrubs and grasses. If this occurred on the side of a mountain the run-off would be higher and muddier than if the forest was still there. This could increase the risk of mudslides that could dam a river or cover houses!

The risk of flooding also increases in urban areas that have more pavement than gardens and parks. Basements would flood more often and rivers running through the town would overflow their banks more often as the run-off into the river flows off the parking lots and streets.

Exercise 2.1: Run-Off Investigation

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