Gravity-Driven Infiltration and Subsidence Phenomena in Posidonia oceanica Residues

A simplified infiltration model for highly permeable porous media was introduced, assuming the matric potential gradient as negligible compared to the gravitational gradient. This model enabled us to determine the delay time, i.e., the time that the water front takes (from the beginning of rainfall) to reach the bottom of the highly permeable layer. Posidonia oceanica (Linnaeus) Delile residues were used as a porous media, in order to study the infiltration process that provides salt leaching under natural rainfall when these residues are arranged in a storage area, before reusing. By using a laboratory rainfall simulator, delay times were measured to verify the applicability of the aforementioned infiltration model. Application of the infiltration model revealed that compaction and subsidence phenomena occurred in such highly permeable porous media. Derivation of an extended formulation was then required to take into account two calibration constants with a clear physical meaning, evidencing the occurrence of a minimum delay time. The calibration procedure enabled a good fit between observed and estimated delay times.