What it shows
A river flowing over loose sediment erodes the outside of each bend, where water moves fastest, and deposits sand on the inside, where it is slow. Over time the bends grow into meanders and may be cut off to leave oxbow lakes, as happens on the Ganga plain.
The science
Moving water carries sediment, and the faster it moves the more it can carry. On a bend, water on the outside travels further and faster, so it picks up sand and cuts the bank back, while the slow inner water drops its load as a point bar. Each bend therefore grows more curved and migrates downstream. When two bends grow close enough, the river breaks through the neck, takes the shorter path and abandons the loop as an oxbow lake.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large plastic tray or a cut-open jerrycan
- Fine sand, about 2 kilograms
- A plastic bottle with a small hole near the base as the water source
- A bucket to catch the outflow
- A few bricks to tilt the tray
- Coloured sprinkles or small confetti to trace the flow
Safety
For this project: Work outdoors or in a bathroom; wipe wet floors at once.
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.
Fill the tray with sand, level it about 3 centimetres deep and raise one end on a brick.
Cut a shallow straight channel from the top to the bottom with a finger.
Fill the bottle, cover the hole, and set it at the top so the trickle runs down the channel.
Let the water run slowly for five minutes and watch where the sand moves.
Drop a few sprinkles in the flow and note that they speed up on the outside of bends.
Keep the flow going and sketch the channel every five minutes.
Raise the brick to increase the slope and compare how fast the channel changes.
When a bend is nearly cut off, photograph or sketch it and label the oxbow lake that forms.
What you should see
A straight channel that turns into a winding one within 15 minutes, with sand deposited on inside bends, steep cuts on outside bends, and at least one cut-off loop.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where does a river erode most on a bend?
On the outside, where the water is fastest.
2What is an oxbow lake?
A loop of river left behind when the river cuts through the neck of a meander.
3Why do rivers on plains meander more than mountain rivers?
The gentle slope lets the water swing sideways instead of cutting straight down.
4Name an Indian river famous for shifting its course.
The Kosi in Bihar.
Take it further
Plant small sprigs of grass along one bank and show how vegetation slows bank erosion.
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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