The degree of saturation=Vw/Vv=Sr. By definition the voids ratio e=Vv/Vs, Porosity n=e/1+e, and e=n/1−n. For saturated soils it may be proved that e=wG, where G. is the specific gravity of the soil. A typical value of e for a soil near Christchurch would be 0.90 at a depth of 9in. The corresponding value of n is 0.45. Therefore, an inch of rain falling on the surface of a dried soil will saturate 2½m. If there is an existing moisture content of 10%, and the soil is saturated at 20% it will saturate 4½in. The saturated moisture content would be 100×0.90/2.65 = 33.5%. Thus, starting from dry conditions—and there are long periods of drought in Canterbury—the ground would be saturated for 9in after 4in of rain. Soil suction would immediately come into action and the moisture would invade the drier zones. The question may then be asked, how much of this water will actually drain downwards to the water table and replenish it? Also, at what stage of this downward Pressure Voids Ratio Curve from Capper & Cassie.