We need to get George and DIED in on this as they can explain permeability and porosity of soils and rocks.

Porosity is indirectly related to hydraulic conductivity; for two similar sandy aquifers, the one with a higher porosity will typically have a higher hydraulic conductivity (more open area for the flow of water), but there are many complications to this relationship. Clays, which typically have very low hydraulic conductivity also have very high porosities (due to the structured nature of clay minerals), which means clays can hold a large volume of water per volume of bulk material, but they do not release water very quickly.

Sorting and porosity

Effects of sorting on alluvial porosity
Well sorted (grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles). The graphic illustrates how some smaller grains can effectively fill the pores (where all water flow takes place), drastically reducing porosity and hydraulic conductivity, while only being a small fraction of the total volume of the material.


In the earth sciences, permeability (commonly symbolized as κ, or k) is a measure of the ability of a material (typically, a rock or unconsolidated material) to transmit fluids. It is of great importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, and of groundwater in aquifers.

The intrinsic permeability of any porous material is:

κI = C X d2

where

κI is the intrinsic permeability [L2]
C is a dimensionless constant that is related to the configuration of the flow-paths
d is the average, or effective pore diameter [L]


] Yes many rocks(not talking about gravel or broken or fractured ones but solid rock layers) can have fluids run through them under pressure. Also clay when dry absorbs water and expands until water will no longer be absorbed and it creates a seal subject to pressure. Porosity is the space between grains of soil or rock and fluid will flow through them limited by force needed to get the fluid through the pore space.

Now George or DIED can fix what I poorly explained.