Structural modules with absorbent elements for drainage and irrigation

A structure for drainage and water-retention a plurality of structural modules arranged adjacent each other, each module comprising a load bearing base unit having a peripheral wall, a top wall and a bottom wall spaced therefrom by at least one supporting element so as to define a volume between the top and bottom walls, the base unit being provided with apertures through the peripheral wall, the top wall and the bottom wall to permit the flow of liquid into and out of the volume;

• wherein each base unit contains a first horizontally extending layer of substantial thickness of a porous foamed polymeric material which occupies at least 25% of the volume within the base unit and absorbs and retains substantial quantities of water that pass into the volume through the apertures;
• and each base unit also contains a second horizontally extending layer of free space of substantial thickness which is vertically displaced from the first horizontally extending layer;
• the modules being arranged adjacent each other vertically so as to provide vertically alternating portions of polymeric material and free space.

A method for providing water to earth beneath a surface layer comprising:

• providing a combined drainage and water retention sub-base layer below the surface layer, the sub-base layer comprising an array of adjacent structural modules, each module comprising a peripheral wall, a top wall and a bottom wall spaced from the top wall by at least one supporting element so as to define an enclosed volume between the top and bottom walls, there being a top array of apertures in the top wall of each module and a peripheral array of apertures in the peripheral wall of each module, wherein at least a first plurality of the modules are occupied by a first horizontally extending layer of a porous foamed polymeric material, and a second horizontally extending layer of free space of substantial thickness which is vertically displaced from the first horizontally extending layer;
• the method further comprising permitting a flow of rain water from the surface layer into each enclosed volume, permitting said rain water to flow from each enclosed volume into the enclosed volumes of adjacent modules to provide drainage;
• absorbing and retaining in the porous foamed polymeric material substantial quantities of said rain, and subsequently releasing the retained rain water to the earth.