Performance Of Permeable Pavement Research Articles

Calibration and validation of DRAINMOD to predict long-term permeable pavement hydrology

The hydrologic performance of permeable pavement varies widely due to underlying soil type, drainage configuration, contributing drainage area, surface infiltration rate, and aggregate depth. A long-term hydrologic model is needed to better understand the influence of these design variables on surface runoff, drainage, exfiltration, and evaporation from permeable pavement systems. Most permeable pavement models have not been calibrated with field monitored data, are usually unable to accurately model internal water storage (IWS) zones, and do not account for evaporation from the aggregate profile. Because permeable pavement employs drainage and exfiltration as primary hydrologic mechanisms, it was hypothesized that DRAINMOD, a model shown to accurately simulate bioretention hydrology, could be calibrated to predict the hydrologic response from permeable pavements. Hydrologic data were collected from two permeable pavement applications in North Carolina (Boone and Durham) and two permeable pavement applications in Ohio (Perkins Township and Willoughby Hills) to calibrate and test the model. The specific permeable pavements applications varied widely in aggregate depth, drainage configuration, underlying soil type, and contributing drainage area. Nash-Sutcliffe Efficiencies for drainage ranged from 0.77 to 0.95 during calibration and validation of all sites. Nash-Sutcliffe Efficiencies for exfiltration/evaporation ranged from 0.55 to 0.97 for Boone and Perkins Township, but prediction of exfiltration/evaporation volumes on an event basis was poor for the remaining two sites due to low exfiltration rates (less than 0.20 mm/hr). Despite this, the cumulative volume of exfiltration/evaporation was predicted to within 1–9 % of what was measured during monitoring. Modeled and monitored surface runoff from the Willoughby Hills application (8 % of the water balance) was equivalent. The model predicted the percentage of drainage, surface runoff, and exfiltration/evaporation to within 2 % of what was monitored/estimated at each site, suggesting long-term modeling of permeable pavement hydrology with DRAINMOD is viable.

Mitigating tire wear particles and tire additive chemicals in stormwater with permeable pavements

6PPD-quinone (6PPDQ) is a recently discovered chemical that is acutely toxic to coho salmon (Oncorhynchus kisutch) and can form via environmental exposure of 6PPD, a compound found extensively in tire wear particles (TWPs). TWPs deposited on roads are transported to aquatic ecosystems via stormwater, contributing to microplastic pollution and organic contaminant loads. However, little is known about the fate of TWPs and their leachable contaminants in these systems. We conducted three experiments at a high school in Tacoma, Washington, to quantify the treatment performance of permeable pavement (PP) formulations, a type of green stormwater infrastructure (GSI), for TWPs and ten tire-associated contaminants, including 6PPDQ. The PPs comprised concrete and asphalt, with and without cured carbon fibers, to improve the mechanical properties of PPs. Pavements were artificially dosed and had underdrains to capture effluent. Three experiments were conducted to evaluate PP mitigation of tire-associated pollution using cryomilled tire particles (cTPs). The 1st and 3rd experiments established a baseline for TWPs and contaminants and assessed the potential for continued pollutant release. During experiment 2, cTPs were applied to each pavement. Our results showed that the PPs attenuated >96 % of the deposited cTPs mass. An estimated 52–100 % of potentially leachable 6PPDQ was removed by the PP systems between the influent and effluent sampling stations. Background 6PPDQ concentrations in effluents ranged from 0 to 0.0029 μg/L. Effluent 6PPDQ concentrations were not explained by effluent TWP concentrations in experiments 1 or 2 but were significantly correlated in experiment 3, suggesting that leaching of 6PPDQ from TWPs retained in the pavement was minimal during a subsequent storm. Our results suggest that PPs may be an effective form of GSI for mitigating tire-associated stormwater pollution. The improved strength offered by cured carbon fiber-amended pavements extends PP deployment on high-traffic roadways where tire-associated pollution poses the greatest environmental risk.

Assessing the Performance of Permeable Pavement in Mitigating Flooding in Urban Areas

In the case of rapid urban development, the impact of extreme climates on the world is gradually increasing, resulting in frequent flood events. However, Taiwan is still in the stage of urban development, and it is necessary to develop more roads. Therefore, determining how to reduce the impact of road engineering on the environment is one of the major issues currently faced. Therefore, a demonstration road of a general pavement and a permeable pavement was built in Dahua North Street, Taoyuan City, Taiwan, and rainwater was stored in a central irrigation ditch and a permeable pavement through an innovative construction method for reuse in agricultural irrigation. In addition, monitoring instruments and management systems were built, and the flow law formula was established, with R2 greater than 0.9. The actual discharge and peak discharge of the permeable pavement and general pavement were analyzed. According to the data analysis results, it can be seen that the permeable pavement can effectively reduce the peak discharge of 60~75%, which not only can achieve the benefit of low-impact development but also can reuse rainwater. The patent application can be used as an example for the application of permeable pavement in Taiwan in the future.

Performance of Permeable Pavement to Filter Stormwater Runoff for Non-Potable Uses in Buildings

Permeable pavement benefits, besides stormwater runoff reduction and groundwater recharge, include stormwater harvesting. As an alternative to water resources scarcity, stormwater that reaches a permeable pavement could be filtered by the same pavement and then used for non-potable purposes in buildings. This work aims to evaluate some types of permeable pavements regarding their performance to remove pollutants from stormwater and decrease runoff. Analyses of infiltration capacity and pollutant concentrations were performed in four permeable pavement models with different types of permeable surface layer (porous asphalt mixture and porous interlocked concrete blocks). Then, the data were used to calculate the “stormwater credits” according to the Minnesota Stormwater Manual. The credits were calculated for volume of runoff, and concentrations of Total Suspended Solids (TSS) and Total Phosphorus (TP). As a result, the models proved adequate to decrease both stormwater runoff and TSS and TP concentrations. Moreover, models with the porous asphalt mixture as a surface layer were more efficient to reduce the concentration of pollutants. However, for the models evaluated in this work, additional treatment is recommended when stormwater harvested from permeable pavements is meant for non-potable uses in buildings.
 Keywords: buildings, stormwater, credits, non-potable uses.

Evaluating the Effectiveness of Low Impact Development Practices against Climate Induced Extreme Floods

Short but extreme flooding events have been frequent and severe globally due to climate change and urbanization in recent years. Similarly, researchers, scientists, and water managers are suggesting the application of sustainable flood management strategies such as Low Impact Development (LID) to mitigate the impacts of such extreme flooding events. However, most of these strategies have primarily been evaluated using historical precipitation events, which may not accurately represent the impact of climate-induced flooding events, which are projected to become more extreme. In this context, this study assesses the effectiveness of LIDs in combating climate change-induced flooding events. The North American Regional Climate Change Assessment Program (NARCCAP) climate model was applied in this study to quantify the magnitude of future projected storm depths, which are expected to increase due to climate change. Similarly, Personal Computer Storm Water Management Model (PCSWMM) was used to develop a rainfall-runoff simulation model and to assess the effectiveness of three LID techniques (Permeable Pavement, Green Roof, and Bio-Retention Cell) in reducing surface runoff under various climate scenarios. The results revealed that under the climate change scenarios the future projected design depths are expected to increase by up to 104%. Similarly, peak discharge, and total flooding volume were found to increase by 37.72% and 88.73%, respectively under the most extreme climate change scenario. Furthermore, the study demonstrated that applying LID strategies decreases peak discharge, offering a viable solution to tackle flooding events induced by climate change. The results illustrated the performance of permeable pavement was superior in reducing the peak discharge by up to 28.57%. Similarly, applying green roofs and bioretention cells reduced the peak discharge by up to 19.93% and 14.25%, respectively.

Analysis of the hydraulic performance of permeable pavements on a layer-by-layer basis

Permeable pavement systems are a sustainable urban drainage technique created with a highly porous base and subbase. This study first analyses the hydraulic performance of several new permeable pavement systems based on 189 experimental hydrographs. In addition, the analysis explores the influence of rain intensity, slope, and, as a novelty, individual layers. Analysed variables were outflow peak, time to peak, and time to specific cumulative discharges. Secondly, based on the experimental hydrographs, the study explores the performance of the permeable pavement module defined in the Storm Water Management Model, carried out in two steps. First, single-layer outflows were used to calibrate parameter values that could not be measured physically, using the differential evolution algorithm and Nash–Sutcliffe model efficiency coefficient as an objective function. Later, complete layout hydrographs were tested without calibration, and model performance was checked. Results show that the superficial permeable interlocking paver layer provides a notably higher retention capacity than the porous asphalt mixture. Individual modelling results show that the soil layer definition is inappropriate for gravel-type layers, even with a geotextile. Despite this, complete section performance is quite good without calibration if the soil layer is not selected on the model. These results are expected to reduce modelling uncertainty, especially when no calibration data is available.

Flood Mitigation Performance of Permeable Pavements in an Urbanised Catchment in Melbourne, Australia (Elizabeth Street Catchment): Case Study

Permeable pavement (PP) systems have been shown to provide onsite stormwater management as well as contaminant removal benefits. Therefore, significant research has taken place in recent years to analyse the performance of these structures in terms of the volume of stormwater harvested and the water quality improvements at small scales. However, there is limited understanding of their performance for reducing stormwater runoff volume to prevent natural disasters, such as catchment-scale flooding. With larger flooding events projected to occur more frequently as a result of urbanisation and climate change, PP systems have the potential to mitigate loss by reducing peak flows and runoff volumes. Therefore, this research investigates the performance of PP at the catchment scale under a range of design rainfall and land-use scenarios. Results indicate that the integration of permeable pavements in urban settings is effective in mitigating surface flooding in an urbanised catchment in Melbourne, Australia by reducing the peak flows by 7–16%. However, in practice, flood reduction ability can markedly decrease with time due to the clogging of pavements. Our results provide preliminary data to show that the integration of permeable pavements into the existing urban landscape can reduce the risk of flooding by providing areas for water to infiltrate if maintained properly. These results are envisioned to assist councils and stormwater managers with the option evaluation of the water-sensitive urban design systems and selecting the appropriate stormwater management measures.

Comprehensive Benefit Evaluation of Pervious Pavement Based on China’s Sponge City Concept

Sponge cities provide broad hydrological functions to alleviate urban flooding and other water-related problems in China. Conventional impervious paving cannot meet contemporary sustainable city goals. The permeable paving technology offers primary benefits such as increasing stormwater infiltration, drainage, purification, groundwater recharge, and microclimatic amelioration. Few studies have evaluated the embracive range of benefits and the social functions holistically. This study aimed to develop a comprehensive benefit evaluation system to cover a broad range of indicators. Nineteen indicators were selected based on the literature review, field studies, and research experience. Organized in a three-tiered hierarchical structure, they were divided into environmental, economic, and social benefits. A grey intuitionistic fuzzy comprehensive evaluation model was built by combining intuitionistic fuzzy analysis with a grey comprehensive evaluation. The computational tools could determine the differential weights of indicators and benefit scores. Taking an example of a permeable pavement project in Quanzhou City, the comprehensive benefits were assessed and validated using our evaluation model. The results show that (1) the comprehensive benefits of the project met the economic feasibility criteria with advantages over conventional paving; (2) the environmental benefits were prominently expressed; (3) the social benefits were assessed and confirmed. The results verified the feasibility and applicability of the quantitative-qualitative model. The method could permit the integrated and systematic benefit assessment of permeable paving designs. It also provides guidance and reference to evaluate the performance of permeable pavements and their comprehensive range of benefits. The findings could reference choosing and refining designs, optimizing the benefits, and promoting a science-oriented development of permeable paving.

Development and Application of Regression Models for Predicting the Water Quality Performance of Permeable Pavement

Development and Application of Regression Models for Predicting the Water Quality Performance of Permeable Pavement

Numerical Analysis on the Optimization of Evaporative Cooling Performance for Permeable Pavements

The phenomenon of urban heat islands is mainly caused by the increase of artificially hardened surfaces in cities, and it can be alleviated by using permeable pavements to dissipate latent heat. There are many disagreements on the cooling effect of permeable pavements, and at present, it still needs more tests and modeling to prove this view. This paper proposes a 3-D transient model based on the heat transfer theory of porous media to accurately evaluate the cooling performance of permeable pavements. The influences of surface thermal parameters, storage depths, and spraying schemes on the cooling performance of permeable pavements are analyzed. The results show that compared with the peak temperature in the dry state, saturated permeable pavements can be significantly reduced. It is also found that the reflectivity of permeable pavements is positively correlated with the magnitude of temperature reduction and it has the most significant effect on the surface temperature among the discussed thermal parameters. A water storage layer with a thickness of 15 cm is recommended to balance economic costs and the cooling performance of permeable pavements. Based on the calculation results of the temperature reduction and cooling time, the optimal quantity of water spray is given innovatively. The proposed model can help improve the material components, structures, and maintenance methods of permeable pavements.

Effect of binder-aggregate ratio on the mechanical and functional properties of porous polyurethane cement mixture

ABSTRACT Polyurethane mixtures are regarded as novel polymer pavement materials that can overcome the shortcomings of poor mechanical properties and loose particles of open-graded friction course (OGFC). Owing to its high strength after curing, polyurethane binder improves the mechanical connection at the aggregate-aggregate contact point, which effectively enhances the service performance of permeable pavement. However, the relationship between the binder content and the mechanical and functional properties of polyurethane mixture has not clearly understood yet. The objective of this study is to investigate the influence of the binder-aggregate ratio on the mechanical and functional properties using laboratory tests. Firstly, the effect of binder content on the mechanical properties of the mixture is examined by Marshall stability test, uniaxial compression test, and bending beam test. Secondly, the functional properties of the mixtures are characterised by Cantabro test, permeability test, computed tomography, and particle clogging test. Finally, the durability of the mixtures is characterised by hydrolysis resistance test and ultraviolet radiation degradation test. The results reveal that the content of binder has a significant impact on the mechanical and functional properties of the mixture. It is necessary to maintain a balance between the mechanical and functional properties.

Influence of pore water phase change on service performance for permeable pavement in Sponge City

Abstract As the cornerstone of normal operation for Sponge City, the service performance of permeable pavement is directly related to the utilization rate of precipitation resources. However, the pore filling state (air, water and ice) of permeable pavement in Sponge City is easily affected by the service environment, especially low temperature. Thus, in the study, the influence of pore filling states and phase change processes on the service performance for permeable pavement were studied based on the models established on specimen section. Details of pore water phase change were visually displayed and described, and the strength variation of Marshall specimens after freeze-thaw cycle experiment also proved the rationality of simulation. Results show that the pore filling states in permeable pavement have different effects on the temperature field, and the influence of pore air on the temperature distribution for permeable pavement is greater than that of pore water (ice). In particular, weak positions between different pores are more susceptible to freezing stress, leading to stress concentration. Simulation results were also verified by macro experiments. Furthermore, the sustainable service performance of permeable pavement in Sponge City was inevitably affected. Therefore, the study results have certain significance for the development of permeable pavement in freezing and thawing regions, and are conducive to the wider application of Sponge City.

Modelling the effect of rainfall patterns on the runoff control performance of permeable pavements.

With the implementation of low impact development (LID) in urban areas, it is necessary to quantify the actual effectiveness of LID facilities. In this study, a coupled hydrology-hydrodynamic numerical model was utilized to investigate the runoff control effectiveness of permeable pavements in the city centre of Shijiazhuang, China. Two groups of designed rainfall events with the same duration but different rainfall amounts and peak rainfall intensity locations were presented, and the effectiveness of permeable pavement was demonstrated by the reduction in the total runoff volume, water depth, and inundated area. The results indicate that the rainfall amount is the main factor affecting the runoff control of permeable pavements, and their effectiveness decreases with increasing rainfall amounts and peak intensity coefficients. Moreover, permeable pavements are more effective in reducing the residential waterlogging area, and the proportion of the inundated area above a depth of 0.2 m is considerably diminished. This study reveals the response of the runoff control of permeable pavements to different rainfall patterns, which is essential for supporting the design and practical operation of permeable pavements.

Mechanical responses analysis and modulus inverse calculation of permeable asphalt pavement under dynamic load

Permeable pavements play an important role in the mitigation of stormwater runoff and urban heat island effect. However, due to low strength and clogging, permeable pavements are always applied in light traffic areas. Therefore, it is necessary to understand the structural performance of permeable pavements under different conditions. In this paper, the performance of two permeable pavement structures (fully-permeable (FP) pavement and semi-permeable (SP) pavement) under dry and wet conditions is analyzed with the finite element method (FEM) modeling and one-third scaled MMLS3 test. A preliminary FEM model was established and empirical values of modulus are used. To make the model more closely simulate the actual conditions of the pavement, the modulus was calibrated according to the MMLS3 test results. The results of resilient strain and calibrated modulus of two structures under dry and wet conditions were analyzed, and the SP structure appears better cracking and moisture damage resistances. The modulus increases firstly and then decreases with the change of loading repetitions, which is considered to be caused by the combined action of further compaction of load and temperature. Since the change rate of surface layer modulus of the SP structure with loading repetitions is higher than that of FP structure, and only the base material of the two structures is different. It can be considered that the base layer modulus will affect the bottom strain of the surface layer, thus affecting the surface layer modulus. Furthermore, by calculating the difference between the base layer and the surface layer, it is found that the smaller the modulus gap between them, the smaller the change rate of the surface layer modulus.

Design measures to mitigate the impact of shallow groundwater on hydrologic performance of permeable pavements

AbstractPermeable pavements (PPs) are widely implemented in urban areas to mimic natural hydrologic processes through enhancing infiltration, and reducing, delaying, and retaining surface runoff. However, its performance can be affected by shallow groundwater since high soil moisture may inhibit its infiltration and exfiltration. This study built a numerical model, which was calibrated and validated based on laboratory experiment data, to evaluate the water balance and retention of PP in shallow groundwater conditions. It assessed the impacts of shallow groundwater and the hydrologic effectiveness of different PP design measures (i.e., building a PP with a smaller storage depth, implementing an underdrain at different elevations, and installing an impermeable liner) on relieving the impacts. Shallower groundwater led to larger amounts of surface runoff and underdrain flow, and a higher chance of saturating the PP reservoir. The three design measures had both benefits and drawbacks in mimicking natural hydrologic cycle and retaining the performance of PP under extreme conditions (e.g., areas of very shallow groundwater tables and/or extreme rainfalls). A PP with a smaller storage depth resulted in less underdrain flow but was prone to saturation. It is, thus, more recommended for PP with more‐permeable subsoils, which can avoid frequent pavement saturation. Although a shallower PP corresponds to a smaller storage volume and shorter hydraulic retention time, it can increase the applicability of PP to shallow groundwater areas, which is beneficial to the regional hydrologic environment. Installing an underdrain generated underdrain flow, which is a burden to the downstream drainage system. However, it significantly reduced the surface runoff and the chance of saturating the PP reservoir, which, thus, is more recommended for PP with less‐permeable subsoils. Comparatively, elevating the underdrain is recommended in areas of shallow groundwater because it can reduce the frequency and amount of groundwater‐induced underdrain flow. In addition, a higher underdrain together with an impermeable liner can create a storage depth, increase the retention duration, enhance exfiltration and evaporation without increasing the saturation risk.

WinSLAMM Simulation of Hydrologic Performance of Permeable Pavements—A Case Study in the Semi-Arid Lower Rio Grande Valley of South Texas, United States

This study used the Source Loading and Management Model for Windows (WinSLAMM) to develop a set of calibrated hydrologic models for three types of regional permeable pavements—porous concrete pavement (PCP), permeable interlocking concrete pavement (PICP), and interlocking block pavement with gravel (IBPG). The objective was to assess the hydrologic performance of permeable pavements, including the runoff depth, peak discharge, percentage increment in runoff reduction of pavements as a function of rainfall depth, development area, and base aggregate porosity, respectively. The permeable pavements were monitored over a wide range of rainfall events in the semi-arid Lower Rio Grande Valley of South Texas. Data regarding rainfall intensities, source characterizations, runoff coefficients, and pavement design were initialized as WinSLAMM input. Validation results showed that the calibrated models could over or under-predict runoff reduction within a 30% error range. PCP and IBPG were very effective and could be capable of handling storms as large as 50-year frequency over a 24-h time period. The modeling results showed that PCP might require a 50–60% lesser footprint area as compared to PICP and IBPG, respectively. Additionally, PCP might be able to store 30% additional runoff if the porosity of base aggregates was increased by 40%.

Laboratory analysis on the surface runoff pollution reduction performance of permeable pavements.

Permeable pavements are used to address the water quality impacts of urbanization. However, few quantitative relations are available on their pollutant removal performance with respect to varying conditions, especially for different components of a permeable pavement. Individually, the water quality performance of the surface pavement layer and gravel layer of a permeable pavement under various conditions was determined in laboratory-scale pavement cells. Our aim was to reveal the manner in which different factors influence the ability of these two layers to remove total suspended solids (TSS), nutrients, including nitrate (NOx-N), ammonia (NH4-N) and phosphorous (TP), chemical oxygen demand (COD), and heavy metals (copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn)), and to provide quantitative understanding of these influences. The removal efficiencies of most stormwater runoff pollutants showed a significant variation with changing rainfall intensity. NH4-N, NOx-N, TP, and TSS removal exhibited statistically negative linear relationship with rainfall intensity. TSS removal was negatively correlated with TSS concentration for the gravel layer, whereas no obvious trend was observed for the surface pavement layer. The statistical results obtained demonstrate that TSS, NH4-N, NOx-N, TP, and COD were removed mainly by the surface pavement layer. A smaller gravel gradation was more effective for removing most pollutants, except for NOx-N and COD. Positive linear relationships were observed between the gravel layer thickness and pollutant (TSS, TP, NH4-N, Cu, and Cd) removal. More importantly, a simple mathematical model was developed to predict the overall performance of the permeable pavement system. By comparing with the overall measured performance, a good performance was achieved, illustrating its promising application in the design of permeable pavements.

Hydrologic Performance of Permeable Pavement as an Adaptive Measure in Urban Areas: Case Studies near Montreal, Canada

AbstractThe infiltration capacity of permeable interlocking concrete pavement (PICP) was characterized on five sites located in the greater Montreal area (Canada). Surface infiltration rates up to ...

Influence of rainfall intensity and pollution build-up levels on water quality and quantity response of permeable pavements

Permeable pavements are part of stormwater management practices known as sustainable urban drainage systems (SUDS). This study describes the influence of several environmental variables, such as the rainfall regime or the pollution build-up level, on the hydraulic and water quality performance of permeable pavements. Four infiltrometers with different configurations of pavement layers were used to study the influence of two rainfall regimes (Atlantic and Mediterranean) and two rainfall intensities (0.5 and 2.2mm/min). The influence of the progressive pollution build-up level was studied by dry sprinkling of road deposited sediments collected with a mechanical street sweeper with a dose of 5g/m2/d. The results show that permeable pavements retained a significant rainwater volume and improved the infiltrated water quality in terms of suspended solids, organic matter and nutrients when compared to the corresponding surface runoff potentially generated from an impervious pavement. The volume of rainwater retained inside them varied between 16 and 66% depending on the variables studied. The water infiltrated from permeable pavements subjected to a Mediterranean rainfall regime contained, in general, higher concentrations of organic matter (22 to 89mg Chemical Oxygen Demand/l) and nutrients (0.6 to 2.1mg Total Nitrogen/l and 0.05 to 0.45mg Total Phosphorus/l) than those under Atlantic regime. However, the latter infiltrated higher loadings in terms of mass. Nitrogen was the substance that infiltrated the most, reaching a 25% of the total mass of nitrogen deposited on the pavements surface. The concentration and mass loading in infiltrated water increased as the pollution build-up level did. The leachability of nutrients and organic matter was greater for high rainfall intensities. The results suggest that it is essential to carry out an adequate cleaning in dry conditions, especially when high intensity rainfall events are foreseen, because of its greater capacity to mobilize pollutants.

Evaluation of surface infiltration performance of permeable pavements

Many different test methods are used in practice to evaluate the surface infiltration performance of permeable pavements. This has led to inconsistency in reporting of test results. This study recognizes the differences in nature between a soil infiltration study and the surface infiltration evaluation of permeable pavements, and identifies the main issues associated with the current practice of surface infiltration testing. It proposes that hydraulic conductivity be adopted as the flow property for measurement and reporting instead of the commonly used infiltration rate. The advantages of measuring hydraulic conductivity are elaborated from both theoretical and practical implementation points of view. The theoretical merits of providing a consistent and integrated treatment of surface infiltration performance of a permeable pavement during the design, construction and maintenance phases are presented. The practical benefits are addressed from the following aspects: consistency between laboratory and field testing, uniformity in reporting of test measurements, rationality in construction quality control and acceptance checking, effectiveness in surface infiltration performance monitoring, and enhanced ability in implementing effective maintenance management. It is emphasized that the techniques and methods needed for measuring hydraulic conductivity of permeable pavement materials, for laboratory testing as well as on-site field testing, are already readily available and have been used by researchers and some practitioners for surface infiltration testing. Two falling-head test methods are recommended: one applies Darcy's law and determines hydraulic conductivity in the conventional way; another measures the time history of falling head and calculates hydraulic conductivity using a modified Darcy equation. It is also highlighted that the measurement of hydraulic conductivity offers a convenient platform for assessing the durability of a permeable pavement against clogging.