PERVIOUS PAVEMENT SYSTEMS
Conventional patios , pathways , roads , and driveways that use traditional concrete or brick and mortar are impervious , meaning that water cannot soak through them ( Clemson Extension-HGIC ). During rainstorms , a much more important problem with impervious surfaces is that all the water runs off rather than soaking into the ground . This significantly increases stormwater runoff which overloads stormwater systems , causing flooding and rapidly drops the salinity of receiving bodies of saltwater . This heavy flow of stormwater carries all sorts of pollutants ( chemicals , nutrients , fecal bacteria ) into the receiving water bodies contributing to non-point source pollution . The work of Holland and Sanger show that watersheds with greater than 10 % impervious surfaces have increased levels of pollutants in tidal creeks . When impervious surfaces of a watershed exceed 20 % -30 %, tidal creek biotic health is impaired . This , and flood prevention , is why replacing impervious surfaces with pervious paving is so important . ( Sanger et al . 2016 ). Low impact alternatives like porous pavement , gravel paths and stormwater infiltration areas ( e . g ., rain gardens ) can help water soak back into the ground , reduce standing water , and minimize the erosion that can result from rainfall flowing off hard surfaces during storms like roofs , driveways , roadways , sidewalks and patios .
PERVIOUS PAVEMENT SYSTEMS
Unlike concrete or asphalt , pervious ( also referred to as porous or permeable ) pavement systems facilitate hydrologic function by allowing stormwater to infiltrate , while still supporting vehicle and pedestrian traffic . In general , these pavement surfaces and profiles have very high infiltration rates relative to compacted soils ( UF- IFAS ; Bean 2019 ). Therefore , these systems allow water to freely infiltrate into an aggregate base or subbase to be stored until the volume soaks into the surrounding subgrade soil , or discharges through an underdrain in a controlled manner ; acting similar to a pervious soil system , and contributing to the replenishment of groundwater . These systems can also reduce pollutant discharge in runoff by filtering the stormwater during its infiltration process to retain particles and associated pollutants at the surface before they reach underground soils . Though pervious pavement systems tend to have higher costs than conventional concrete or asphalt , costs can be saved by eliminating / reducing the need for conventional stormwater infrastructure ( ASCE , 2015 ). Consultation with professional engineers or contractors is required when considering the implementation of pervious pavements so they are designed in accordance with Charleston County Permitting Standards . Most of the specifications and recommendations herein originate from the County Stormwater Program ’ s second edition of the Permitting Standards and Procedures Manual produced in 2017 .
Site Selection
Suitable sites for pervious pavements are any location where pavements are currently located or planned to be located . This includes pedestrian walkways , bike pathways , pool decks , leisure trails , driveways , cart paths , and some roadways .
Materials
Surface materials vary and should be considered based on the appropriate load bearing capacity , permeability , and desired aesthetics . Load bearing should be based on the appropriate forms of traffic ( e . g ., pedestrians , heavy trucks ) to be expected within the area . It is important to analyze profile depths required to meet the hydrologic and structural requirements for a permeable pavement design to determine the system ' s profile . Typically , the hydrologic design and load bearing capacity determines the profile depth ( Federal Highway Administration , 2012 ; Bean et al . 2019 ). The top pavement and bedding course layers have set thicknesses ; however , the reservoir base course depth is adjusted to meet the required profile design depth . For some surfaces , such as porous asphalt ,
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