Which soil type is most permeable?

Gravel is the most permeable soil type due to its larger particle size and the significant spaces between those particles, which allows water to flow through it much more easily than through finer soils. The structure of gravel, characterized by coarse grains, creates pathways for water movement, leading to high infiltration rates. This property makes gravel particularly advantageous in drainage applications and for construction purposes where rapid water movement is desired.

In contrast, clay has very fine particles that are compacted tightly together, resulting in minimal pore spaces, which restricts water movement significantly. Organic soil, which contains decomposed plant material, tends to retain moisture and can also limit permeability. Silt, being finer than sand but coarser than clay, has moderate permeability, but it is still not as effective as gravel in allowing water to pass through quickly. Therefore, gravel stands out as the soil type with the highest permeability among the choices provided.