 Regular maintenance is required to prevent crust forming.Porous paving (or pervious paving) is an alternative to conventional impermeable pavement and allows infiltration of runoff water to the soil or to a dedicated water storage reservoir below it In reasonably flat areas such as car parks, driveways and lightly used roads, it decreases the volume and velocity of stormwater runoff and can improve water quality by removing contaminants through filtering, interception and biological treatment.Porous pavements can have several forms and are either monolithic or modular.