Water Quality Improvement Performance of Geotextiles Within Permeable Pavement Systems: A Critical Review

Performance synergism of pervious pavement on stormwater management and urban heat island mitigation: A review of its benefits, key parameters, and co-benefits approach

Pervious pavement system (PPS) is a suitable alternative technique for mitigating urban flooding and urban heat island (UHI) simultaneously. However, existing literature has revealed that PPSs cannot achieve the expected permeability and evaporation. To overcome this gap, this study presents an elaborate review of problems associated with PPSs and highlights its benefits to stormwater management and UHI mitigation. We determined key parameters of PPSs that could influence urban flooding and UHI mitigation, including hydrological properties, thermal physical properties, structure design, and clogging resistance. We identified the co-benefits approach of PPS towards performance synergism on stormwater management and UHI mitigation from quality controlled design and fabrication, periodic maintenance, and effective evaluation system based on practice environments. The results indicate that existing studies of PPSs primarily focus on permeability, while little emphasis is given to the evaporative cooling performance, leading to a biased development with a loss of test standards and regulations that cannot control the cooling potential of the system. The performance synergism of permeability and evaporative cooling in PPS should be studied further, while considering quality control of the materials and in-situ practice design. Parameter controls (with commonly used standards) during fabrication, periodic maintenance (during operation), and pre- and post-evaluation processes of PPSs should work collectively to achieve optimal benefits and reduced costs.

Sustainable Urban Street Comprising Permeable Pavement and Bioretention Facilities: A Practice

Roadside bioretention and permeable pavements have proven effectiveness in rainwater filtration and waterlogging mitigation, but conventional street design approach could not accommodate their work in conjunction. In this research, possible roadside facilities allowing water transmission from permeable pavements and bioretention to the pipe system are proposed. Hydraulic properties of the comprised elements were analyzed, including rainfall intensity, permeable pavements, soil layers and pipe systems. A transformation method was formulated to obtain a successive time-intensity formula from conventional design parameters to describe the rainfall behavior, and therefore the water retention capacity of the bioretention could be considered. A test section of 1.6 km combining permeable pavements and roadside bioretention was constructed, and its hydraulic performance was predicted based on the proposed design method and Storm Water Management Model (SWMM). The research results suggest that the bioretention facilities and permeable pavements cooperate well in the test section. In a light rain event, the proposed street has favorable performance in rainwater collection and filtration. In a relatively intense rainstorm event, the street collects and filters water in the initial stage, but will have similar hydraulic performance to a conventional street once the retention facilities are saturated. Thus, no reduction in diameters of drainage pipes from conventional designs is suggested in similar projects.

Influence of filter layer positions and hydraulic retention time on removal of nitrogen and phosphorus by porous asphalt pavement

This study was aimed to investigate the removal processes of nitrogen (TN), NH₄ ⁺-N and phosphorus (TP) from surface runoff by performing experiments on the filter layers in porous asphalt pavement (PAP). Experiments were conducted to compare the differences of the filter layer placed at the top, the middle or the bottom of PAP. The effects of retention time on the removal of the pollutants and the adsorption capacity of PAP materials were also investigated. Results indicated that the filter layer placed under the bed course improved the removal rates of pollutants compared to the other two cases on the whole. The concentration of TP in the effluent decreased by 80% after the 48 h retention time. In conclusion, this study demonstrated that the positions of filter layers and the temporary retention time of surface runoff within the bed course of PAP were critical parameters for determining the removal processes of pollutants. Thus, a certain retention time for surface runoff in bed course is of great importance for PAP to serve as an effective low impact development technology for stormwater management.

Drivers of changing urban flood risk: A framework for action

This study focuses on drivers for changing urban flood risk. We suggest a framework for guiding climate change adaptation action concerning flood risk and manageability in cities. The identified key drivers of changing flood hazard and vulnerability are used to provide an overview of each driver's impact on flood risk and manageability at the city level. We find that identified drivers for urban flood risk can be grouped in three different priority areas with different time horizon. The first group has high impact but is manageable at city level. Typical drivers in this group are related to the physical environment such as decreasing permeability and unresponsive engineering. The second group of drivers is represented by public awareness and individual willingness to participate and urbanization and urban sprawl. These drivers may be important and are manageable for the cities and they involve both short-term and long-term measures. The third group of drivers is related to policy and long-term changes. This group is represented by economic growth and increasing values at risk, climate change, and increasing complexity of society. They have all high impact but low manageability. Managing these drivers needs to be done in a longer time perspective, e.g., by developing long-term policies and exchange of ideas.

Effects of OASIS® phenolic foam on hydraulic behaviour of permeable pavement systems

Sustainable drainage is a major challenge for highway and environmental agencies to mitigate flooding and understand the optimum design parameters of pavement structure. This paper experiments the hydraulic properties of OASIS^® phenolic foam material examining infiltration rate and steady-state behaviour, water storage capacity of different thicknesses of OASIS^® material, and the effect of OASIS^® material in deferring the water peak flow during rainfall intensities of 100 mm/h, 243 mm/h, 400 mm/h, and 563 mm/h. This paper designs an application programme that estimates the optimal thickness of OASIS^® layer to retain 100% of stormwater for a duration of 15 min. The results from laboratory tests corroborate the performance efficiency of OASIS^® material to delay peak stormwater flow and mitigate flooding. The OASIS^® materials not only increase the ability of permeable pavement system to absorb and retain stormwater up to a saturation limit but also retain the nutrient contaminants infiltrate to groundwater. The designed application programme will help the designers and constructors to increases the drainage efficiency of pavement structure by estimating the optimal thickness of OASIS^® layer required to delay peak stormwater flow during maximum rainfall intensities.

The Influence of Geotextile Type and Position in a Porous Asphalt Pavement System on Pb (II) Removal from Stormwater

Porous asphalt (PA) pavement systems with and without a geotextile layer were investigated in laboratory experiments to determine the impacts of the geotextile layer on the processes leading to lead ion (Pb2+) removal from stormwater runoff. Two types of geotextile membranes that were placed separately at upper and lower levels within the PA systems were tested in an artificial rainfall experiment while using synthetic rainwater. The effect of storage capacity within the system on Pb2+ removal was also investigated. Results indicated that the use of a geotextile layer resulted in a longer delay to the onset of effluent. The non-woven geotextile membrane that was placed below the reservoir course improved the Pb2+ removal rate by 20% over the removal efficiency of the system while using a woven geotextile placed just below the surface but before the choker course. Pb2+ ions were reduced by over 98% in the effluent after being held for 24 h in reservoir storage. Results suggest that temporary storage of stormwater in the reservoir course of a PA system is essential to improving Pb2+ ion removal capability.

Clogging in permeable concrete: A review

Permeable concrete (or "pervious concrete" in North America) is used to reduce local flooding in urban areas and is an important sustainable urban drainage system. However, permeable concrete exhibits reduction in permeability due to clogging by particulates, which severely limits service life. This paper reviews the clogging mechanism and current mitigating strategies in order to inform future research needs. The pore structure of permeable concrete and characteristics of flowing particulates influence clogging, which occurs when particles build-up and block connected porosity. Permeable concrete requires regular maintenance by vacuum sweeping and pressure washing, but the effectiveness and viability of these methods is questionable. The potential for clogging is related to the tortuosity of the connected porosity, with greater tortuosity resulting in increased potential for clogging. Research is required to develop permeable concrete that can be poured on-site, which produces a pore structure with significantly reduced tortuosity.

Potential tree species for use in urban areas in temperate and oceanic climates

This study aims to assess the potential of trees for integration in urban development by evaluating the damage caused by trees in relation to various tree characteristics. Tree damage to permeable pavement systems and other urban structures such as impermeable pavements, kerbs, roads, retaining walls, footpaths, walls and buildings were assessed to identify the most suitable trees for the urban environment. One hundred square sites of 100 m × 100 m were randomly selected in Greater Manchester for this representative example case study to demonstrate the assessment methodology. Among tree species in this study, Acer platanoides L. (Norway maple) occurred most frequently (17%); others were Tilia spp. L. (Lime; 16%), Fraxinus excelsior L. (common ash; 12%), Acer pseudoplatanus L. (sycamore; 10%) and Prunus avium L. (wild cherry; 8%). The study concludes that 44% of the damage was to impermeable pavements and 22% to permeable pavements. Other damage to structures included kerbs (19%), retaining walls (5%), footpaths (4%), roads (3%) and walls (3%). Concerning the severity of damage, 66% were moderate, 21% light and 19% severe. Aesculus hippocastanum L. (horse chestnut) caused the greatest damage (59%) expressed in percentage as a ratio of the tree number related to damage over the corresponding tree number that was found close to structures.