What it shows
Terracing and ploughing along the contours slow rain runoff and hold soil on hillsides. A sand tray model measures the soil and water lost on each slope.
The science
Water running down a slope picks up soil and carries it away. Steps and ridges across the slope slow the water, give it time to soak in and trap soil behind them. That is why hill farmers build terraces and plough across the slope.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three plastic trays or boxes with a spout at one end
- Garden soil or sand
- A watering can with a sprinkler head or a perforated bottle
- Three catch cups
- A tilted board or books
- A measuring cup and a kitchen scale
Safety
For this project: Work outdoors or over a tray. Wash hands after handling soil. Do not use trays near electrical items.
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 each tray with the same mass of soil and tilt each to the same angle.
Leave tray 1 as a smooth slope.
Shape tray 2 into three flat steps (terraces) with small lips.
Make tray 3 a smooth slope with shallow furrows drawn across the slope.
Place a catch cup at the spout of each tray.
Pour the same 1 litre of water evenly over each tray with the sprinkler.
Measure the volume of runoff water and dry and weigh the soil that came out.
Compare runoff and soil loss in a table and chart.
What you should see
The smooth slope loses the most water and soil, and the terraced and furrowed trays lose much less. The chart shows the benefit of each method.
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 runoff?
Water that flows over the ground instead of soaking in.
2How do terraces help?
They slow water and trap soil.
3What is contour ploughing?
Ploughing across a slope rather than down it.
4Where are terraces used in India?
In hill states such as Uttarakhand and Himachal Pradesh.
Take it further
Plant grass seeds on one tray and test the effect of vegetation cover as well.
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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