The total porosity less the porosity filled with clay mineral bound water.

The total volume of interconnected pore spaces in a medium divided by the total volume of the medium. Analogous to specific yield. Note that porosity is always equal to or higher than effective porosity, because not all pore spaces are interconnected.

In hydrologic terms, the ratio, usually expressed as a percentage, of the volume of water or other liquid which a given saturated volume of rock or soil will yield under any specified hydraulic condition, to the given volume of soil or rock.

The amount of interconnected pore space through which fluids can pass. Effective porosity is usually less than total porosity because some dead-end pores may be occupied by static fluid.

1. The volume of the voids that conduct water divided by the volume of the sample; equal to or less than the porosity. 2. The portion of the porosity that can be drained by gravity forces; equal to the porosity minus the residual water content.