What it shows
Roof rain can be led through a filter pit into the ground to raise the water table. The model shows how a recharge pit with gravel and sand layers refills a borewell.
The science
Rain that runs off a roof is wasted unless it is led to a pit. In the pit, gravel and sand filter the water as it seeps down to the aquifer. The extra water raises the water level in nearby wells and borewells.
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 clear plastic bucket or box
- Gravel, coarse sand and fine sand
- A perforated plastic tube as the borewell
- A small tray roof with a downpipe made from a bottle
- A watering can for rain
- A ruler and marker
- A cup of dye for tracing
Safety
For this project: Cut plastic with an adult. Keep the model on a stable table over a tray, and wash hands after handling gravel and sand.
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 bucket with sand to a depth of 15 cm and stand the perforated tube in the middle.
Add water slowly until it fills the lower 5 cm of sand and mark the starting water level in the tube.
Make a pit by hollowing a small hole near the tube and filling it with layers of gravel and sand.
Place the roof tray on the bucket edge and connect its downpipe to the pit.
Pour 1 litre of dyed rain from the watering can onto the roof.
After ten minutes, measure the rise of water in the tube.
Repeat without the pit and compare the rise.
Draw a diagram of the model and mark the flow of water.
What you should see
The tube’s water level rises after the pit is used and rises much less without it, showing the benefit of recharging.
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 groundwater recharge?
Adding water to the aquifer.
2Why layer gravel and sand?
To filter the water as it enters.
3Why is the water level in the borewell important?
It decides how deep the pump must go.
4Why is roof water a good source?
It is cleaner than ground runoff.
Take it further
Time how fast the water drains in the pit with different sand mixes.
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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