What it shows
A watershed is the land that drains to one river. Spraying water on a crumpled sheet shows ridges, valleys and how water, and anything on the ground, ends up in the stream.
The science
Water flows downhill under gravity, following the lowest path. Ridges divide the water into separate watersheds, and valleys gather it into streams. Pollution dropped on the land is washed down to the same stream, so what happens upstream affects everyone downstream.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large sheet of thin paper or an old newspaper
- A waterproof tray or a plastic sheet
- Washable markers in two or three colours
- A spray bottle of water
- Cocoa powder or tea as pretend pollution
- A pencil and ruler
Safety
For this project: Use only washable markers and food-safe powders. Cover the table with a plastic sheet and wipe up water after use.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Crumple the paper tightly, open it out and lay it on a tray to form hills and valleys.
Trace the highest ridge lines in one colour of marker.
Trace the valley lines in another colour, where you think streams will flow.
Lightly spray the paper with water and watch the marker lines bleed along the water paths.
Sprinkle a little cocoa powder on one hill to stand for pollution.
Spray again and see where the colour flows.
Label the main stream, tributaries and the outlet.
Draw a clean map of the watershed with arrows showing the flow.
What you should see
The paper shows ridge lines separating areas and valleys joining into a main stream, and the cocoa shows how pollution travels downstream.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a watershed?
The land area that drains into one river or lake.
2What is a ridge?
The high line that divides one watershed from the next.
3Why does pollution travel?
Flowing water carries it along.
4Which large watershed is near you?
The river basin your town lies in, such as the Ganga or Godavari.
Take it further
Find the real watershed boundaries of your local river on a map and compare with the model.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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