Gravel, sand or clay?

The idea

Water infiltrates more readily where the spaces between soil and rock particles are wider, open and interconnected, so it seeps fastest through gravel, slower through sand and slowest through clay.

Same water, three soils

The same amount of water is poured on gravel, sand and clay.

Which one lets the water through fastest?

• Gravel
• Sand
• Clay

Pour on all three

Press the button and watch the three tubes.

Look at the gaps

The gravel has the widest spaces between its particles, so water went down first. Sand has smaller spaces and clay the smallest.

Water infiltrates more readily where the spaces between soil and rock particles are wider, open and interconnected, so it seeps fastest through gravel, slower through sand and slowest through clay.

• Soil | Spaces between particles | Water seeps
• Gravel | Widest | Fastest
• Sand | Smaller | Slower
• Clay | Smallest | Slowest

Notes

Water infiltrates more readily where the spaces between soil and rock particles are wider, open and interconnected, so it seeps fastest through gravel, slower through sand and slowest through clay.

Check yourself

Through which does water seep fastest?

Through which does water seep slowest?

Why does water seep fast through gravel?

Put these in order from fastest to slowest seepage.

• Gravel — correct. Yes!
• Sand. Water seeps through sand more slowly than through gravel.
• Clay. Clay is the slowest of the three.
• Gravel. Gravel is the fastest of the three.
• Clay — correct. Yes!
• Sand. Sand is slower than gravel but faster than clay.
• The spaces between gravel particles are narrower. Gravel has the widest spaces, not narrow ones.
• Gravel particles soak up all the water. The water goes through the wide spaces between particles.
• The spaces between gravel particles are wider — correct. Yes!
• Gravel, sand, clay — correct. Yes!
• Clay, sand, gravel. That is the order from slowest to fastest.
• Sand, gravel, clay. Gravel is faster than sand.