text: Permeable solutions can be based on porous asphalt and concrete surfaces, concrete pavers (permeable interlocking concrete paving systems – PICP), or polymer-based grass pavers, grids and geocells. Porous pavements such as pervious concrete and pervious asphalt are better suited for urbanized areas that see more frequent vehicular traffic, while concrete pavers, grids, and geocells are better suited for light vehicular traffic, pedestrian and cycling pathways, and overflow parking lots. Pervious concrete pavers allow water to percolate and infiltrate through the pavers and into the aggregate layers and/or soil below. Impervious concrete pavers installed with ample void space between each paver function in the same way as pervious concrete pavers as they enable stormwater to drain into the voids between each paver, either filled with coarse aggregate or vegetation, to a stone and/or soil base layer for on-site infiltration and filtering. Polymer based grass grid or cellular paver systems provide load bearing reinforcement for unpaved surfaces of gravel or turf.
  Grass pavers, plastic turf reinforcing grids (PTRG), and geocells (cellular confinement systems) are honeycombed 3D grid-cellular systems, made of thin-walled HDPE plastic or other polymer alloys. These provide grass reinforcement, ground stabilization and gravel retention. The 3D structure reinforces infill and transfers vertical loads from the surface, distributing them over a wider area. Selection of the type of cellular grid depends to an extent on the surface material, traffic and loads. The cellular grids are installed on a prepared base layer of open-graded stone (higher void spacing) or engineered stone (stronger). The surface layer may be compacted gravel or topsoil seeded with grass and fertilizer. In addition to load support, the cellular grid reduces compaction of the soil to maintain permeability, while the roots improve permeability due to their root channels.
  In new suburban growth, porous pavements protect watersheds by delaying and filtering the surge flow. In existing built-up areas and towns, redevelopment and reconstruction are opportunities to implement stormwater water management practices. Permeable paving is an important component in Low Impact Development (LID), a process for land development in the United States that attempts to minimize impacts on water quality and the similar concept of sustainable drainage systems (SuDS) in the United Kingdom.
  The infiltration capacity of the native soil is a key design consideration for determining the depth of base rock for stormwater storage or for whether an underdrain system is needed.