Water management systems and methods of constructing water management systems comprising two-dimensional arrays of cells. Each cell has a base and a cell top module stacked on the base, the cell top module having a top flange and at least one top leg, a lower end of which engages the base. A base of one system has a bottom leg with an upper end cavity configured for a lateral clearance fit of a lower end portion of the top leg. The cavity holds at least one stacked spacer and is filled with a flowable substance after the top leg is inserted and positioned on the spacer. The flowable substance hardens to fully seat the lower end portion of the upper leg. Another system series of the cell top flanges being held together by tension cables extending therethrough.