Treatment MeasuresPorous Paving
More Information
Porous paving is an alternative to conventional impermeable pavements with many stormwater management benefits. These surfaces allow water to percolate through to a sub-surface course, from where it infiltrates to the soil. Further information can be found in Chapter 14.4 "Other Measures" in the WSUD Engineering Procedures available for purchase from CSIRO publishing.
A number of porous paving products are commercially available including:
- pavements made from special asphalts that allow stormwater to filter through the pavement surface
- concrete grid pavements that allow stormwater to filter through voids in the concrete
- plastic modular block pavements that allow stormwater to filter through voids in the plastic matrix.
Porous paving can be utilised for a variety of water management objectives:
- reduced peak stormwater discharges from paved areas
- increased groundwater recharge
- improved stormwater quality
- reduced area of land dedicated solely to stormwater management.
Advantages
- Retains pollutants close to source
- Reduces site run-off, attenuates flood peaks and increases groundwater input
- Can be aesthetically more pleasant than conventional drainage channels.
Disadvantages
- Can only support light traffic loads
- Pavement clogging can reduce effectiveness
- Possible risk of groundwater contamination
- Only suitable for mildly sloped sites
Asphalt Porous Paving
Asphalt porous paving is laid on a sand/gravel sub-base over natural soil.
The asphalt porous paving system operates by rainfall percolating through a porous asphalt layer to the sub-base. Stormwater is stored in the sub-base until it infiltrates to the surrounding soil. When the surrounding soil is impermeable, subsoil drainage is installed below the sub-base to allow stormwater to overflow to the street drainage system.
Concrete Grid & Plastic Modular Block Porous Paving
There are many different types of concrete grid porous pavement systems, including concrete poured in-situ, precast concrete grids and modular pavers. Plastic porous paving is usually used in modular block form. The concrete or plastic pavers contain many evenly spaced void areas that are filled with sand, gravel or grass. The pavers are typically placed on a sand or gravel base.
Concrete grid pavers can retain heat in hot climates, thereby decreasing the viability of grass grown in the pavement voids. Plastic modular block pavers are better suited to the growth of grass in hotter climates.
Modern design practice includes retention trenches placed below the sand/gravel layer and an overflow to the street drainage system. The paving operates by allowing rainfall to percolate through the voids between the pavers to the sand/gravel layer, and subsequently through the geotextile fabric to the retention trench. This forms a very effective stormwater quality treatment chain. Stormwater in the retention trench infiltrates to the surrounding soil and, when necessary, overflows to the street drainage system.