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Permeable pavements and parking lots are often constructed in urban settings to facilitate storm water runoff and mitigate urban flooding and storm water overflow risks. Though they are usually built from conventional materials (sustainable, recycled alternatives such as recycled glass are also available), permeable pavements build on ecosystem services provided by soil, allowing water capture and infiltration. The permeable surfaces provide greater water uptake. The water is infiltrated, and to an extent purified, before recharging the groundwater. The resulting retention decreases runoff rates and reduces pressures on urban storm water systems.
There are various types of permeable pavement, including permeable asphalt, permeable concrete, concrete grid pavers, loose gravel or stone-chippings, resin-bound paving, and porous plastic “pavement” structures designed to have grass growing in the pores. The general design includes a permeable surface structure that allows water containing relatively coarse solid to pass through to an underlying reservoir where it is collected and stored. It can then slowly infiltrate into the compacted subgrade layer, trapping sediments and other finer materials, before eventually reaching the groundwater. Some systems also have under drains connected to the sub-base reservoirs for the purpose of transporting the water to the urban storm drain system.
As the frequency and strength of extreme weather events increase, permeable pavements and parking lots can help mitigate flooding and overflow risks from could bursts in urban and semi-urban settings. An additional benefit is mitigation of the urban heat island effect.