Egypt Primary 5 Science, Week 22: A model watershed

Cleaning used water, a model watershed and thirst by the sea

Week 22 · Theme 3 Protecting Our Planet, Unit 3 Our Earth’s Resources, Concept 3.3 (C), Unit Project We All Live Downstream, Interdisciplinary Project Water by the Sea (A) · 3 lessons

A model watershed

Discovery Education Science P5: Term 2, Unit 3, pp. 82–85

GoalUse a model watershed to see how pollution travels downhill, and explain what “we all live downstream” means.

New words

watershed · all the land whose water flows to the same stream, river or lakedownstream · farther along a river, in the direction the water flowsmodel · a small copy or drawing that helps us understand something big

Explanation

Rain that falls on high ground runs downhill. Small streams join bigger ones, and the water collects in a river, a lake or the sea. The land that drains to one place is a watershed. Because water always flows downhill, anything it carries goes along: soil, rubbish, oil from a leaking engine. So pollution that enters a stream high up will travel and reach the people, plants and animals below. That is why people say, “We all live downstream.” A model helps us see this. It is smaller and simpler than the real thing, so it leaves things out, such as real soil and rain, but it lets us test a question safely. When we pour pollution on the high end of a model, we can watch where it goes and think about how to stop it.

high ground: a stream starts→a village→a farm→a town→the sea

Worked examples

Model watershed (a grown-up helps): wrap a baking tray in foil, make hills with clay and prop one end on a book. Pour 500 mL of water slowly on the high end and watch it run down into the low end.

Trial	What we poured	What we saw (example)
1	clean water	it ran down to the low end
2	water and coloured oil	oil spread down to the low end

Now add a few spoons of cooking oil coloured yellow with a pinch of turmeric near the top, as if a leaking engine had spilled it. Oil does not mix with water: it floats and spreads in a coloured film that the water carries down to the low end of the tray. The pollution does not stay where it started.

In the model	In real life
pouring water	rain
foil	ground and soil
oil	pollution

Look at the limits of the model. Real rain falls from the sky, real soil soaks up water, and real rivers are far longer. A model is still useful because it lets us ask, “If something spills here, who is affected?” without harming anything.

Class activity

Build the model watershed (a grown-up helps; do it outdoors or on newspaper). You need a baking tray, foil, clay, a book, 500 mL of water, a little cooking oil coloured with a pinch of turmeric (food colouring does not mix into oil), and paper towels. Wrap the tray in foil, add clay hills, and prop up one end. Write a prediction. Pour the water slowly on the high end and watch. Then pour a spoon of coloured oil near the top and pour water again. Write what happened to the oil. Wipe up with paper towels and never pour oil down a drain. Wash your hands.

Practice

What is a watershed?

A stream runs from a farm (B) past a village (D) and a town (A) to the sea (C). The farm lets some chemical wash into the stream. Which place does the pollution reach first after the farm? Say the letter.

Why does oil from a model spill spread down the tray?

Give one way the model is different from a real watershed and one way it is useful.