Download Porosity and permeability

Porosity and permeability
The porosity of the soil is the percent of the soil that is air space. Porosity
ultimately affects the amount of water a particular rock type can hold and
depends on a couple of different factors;
• Particle shape - round pebbles have greater porosity than angular ones
sorting - when particles are all the same size porosity is greatest
The ability of the ground water to pass through the pore spaces in the
rock is described as the rock's permeability. Permeable layers of rock
that store and transport water are called aquifers. While porosity and
permeability usually go hand-in-hand, though some porous rocks are not
permeable and some impermeable rocks are porous. Permeability is
affected mostly by the size and arrangement of the grains in the soil.
• Grain size - larger grains are more permeable
The Water Table
• As rain and runoff enter the soil the water begins to fill the pore spaces in
the ground. The water will continue to work its way down until it
accumulates above an impermeable layer (bedrock). Just like the soil
horizons the areas of saturated an partially saturated soils can be defined
as layers (bottom up) .