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Article

Innovation in Water Management: Designing a Recyclable Water Resource System with Permeable Pavement

by
Shu-Rong Yang
1,
Xing-Rong Chen
1,
Hao-Xuan Huang
1 and
Hsin-Fu Yeh
2,*
1
Department of Civil Engineering, National Pingtung University of Science and Technology, Pingtung 912, Taiwan
2
Department of Resources Engineering, National Cheng Kung University, Tainan 701, Taiwan
*
Author to whom correspondence should be addressed.
Water 2024, 16(15), 2109; https://doi.org/10.3390/w16152109
Submission received: 18 June 2024 / Revised: 17 July 2024 / Accepted: 21 July 2024 / Published: 26 July 2024
(This article belongs to the Section Urban Water Management)
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Abstract

:
Taiwan’s unique geographic environment combined with climate change leaves it particularly vulnerable to water shortage issues. A new water resource recycling system that adheres to a Low Impact Development (LID) concept and utilizes existing permeable pavement techniques to mitigate water scarcity is presented in this study. The design routes water at the base and subbase layers of a permeable pavement toward a planter box in the median divider island or box culvert below the median divider island. Once the runoff has flowed into the bottom of the planter box or box culvert, it is available for plants via soil capillary action. Through evaporation or transpiration, the water is then returned to the atmosphere and integrated into the water cycle for localized microclimates. This study used a 3D printer to create a small-scale model of the proposed design. Using this small-scale 3D model, a series of capillary experiments were conducted to evaluate the permeable pavement water recycling system. Because the small-scale model is not suitable for long-duration tests, soil column experiments were also used. The soil was compacted to different relative compactions for a 3D model and the soil column experiments were used to evaluate the capillary rise height of the soil. The results showed that when using a silt with low plasticity soil (ML), under low relative compaction, the capillary water can reach the rooting level of appropriately selected plants. Therefore, if the soil around vegetation is correctly compacted, the vegetation’s roots will have access to stored water. The proposed permeable pavement water recycling system represents a practical approach to managing stormwater runoff and achieving water conservation objectives. This innovative design not only aims to conserve and protect water resources but also supports sustainable water management practices, thereby helping to mitigate the impacts of climate change.

1. Introduction

As the climate continues to change, water resource management in Taiwan has become more challenging. In particular, the intensity and frequency of extreme precipitation events are increasing but the duration of each event is decreasing and the time between events is lengthening, leading to an increase in both droughts and floods. Furthermore, the steep, relatively short rivers of Taiwan quickly direct all runoff to the ocean, and it is difficult to store any on land. The combination of short, infrequent precipitation events combined with rapid runoff is leading to water scarcity issues [1,2,3].
Worldwide, human activities and natural disasters have brought enormous stress to the water environment. This is particularly true in cities, where rapid urbanization has led to a more impervious area and less infiltration, which in turn has intensified runout and flood problems [4]. In Taiwan, the effects of urbanization are compounded by the increasing frequency of droughts and floods. In addition, water contamination from municipal, industrial and livestock wastewater as well as non-point source pollutants makes much of the water that is stored on land unusable without additional treatment [5,6,7,8,9].
Maintaining urban permeability constitutes a fundamental aspect of contemporary urban planning, particularly pivotal amid escalating urbanization and the challenges posed by climate change. Urban permeability encompasses the natural capacity for water and air to flow within and around cities, directly impacting the health of urban ecosystems and residents’ quality of life. Enhancing urban permeability contributes to increased land permeability, decreased flood risks, enhanced water quality, and preservation of groundwater resources. Moreover, it facilitates natural ventilation, mitigates urban heat island effects, improves air quality, and fosters a more comfortable living environment for residents. Implementing effective strategies to enhance urban permeability, such as integrating green infrastructure, utilizing permeable materials, and advancing stormwater management systems, enables cities to better confront the impacts of climate change, achieve sustainable development objectives, and establish more habitable urban environments for future generations [10,11,12,13,14].
In recent years, there has been a significant increase in studies focusing on improving water resource management. Among these studies, the concept of a “sponge city” has emerged as a prominent approach in urban water management [15,16]. A sponge city operates like a sponge, efficiently absorbing water and adapting to significant fluctuations in rainfall patterns. This concept underscores the adoption of a Low Impact Development (LID) philosophy, which aims to mitigate runoff from intense precipitation events and address issues related to flooding and water pollution [17,18]. LID represents a sustainable approach to stormwater management by implementing decentralized, micro-scale control measures that mimic natural hydrological processes [19,20,21,22]. In Taiwan, the application of LID techniques has demonstrated significant success, achieving an average reduction in runoff of approximately 30% [23,24,25].
Common LID approaches include rain gardens/bioretention, green roof, grass swales and rain barrels [26,27]. In comparison to a natural surface waterbody, urban expansion affects water resources and water quality by increasing the runoff rate and volume, decreasing infiltration, and decreasing groundwater recharge and base flow, leading to a deterioration of water quality [28,29]. Since roads make up a large proportion of the surface area of urban environments, the potential to utilize roads for rainwater retention is high. Permeable pavement, as another LID approach, facilitates the infiltration and passage of rainwater through its surface, thereby replenishing the underlying soil water reservoir. A successful permeable pavement integrates both structural and hydrologic design considerations. Structural design ensures the pavement can withstand vehicle loadings without failure, while hydrologic design focuses on the capacity needed to effectively infiltrate, store, and release water, thereby enhancing stormwater management practices [30]. Consider selecting a type of permeable pavement layer that best meets the requirements for traffic and infiltration capacity. For example, porous asphalt or pervious concrete may be preferable for certain slope conditions, while permeable interlocking concrete and grid pavements might be more suitable for areas where vehicles frequently turn. Permeable pavements are generally recommended to have slopes of less than 5 percent [30]. Much of the literature on permeable pavement has compared the permeability of the different pavements and the ability of the pavements to reduce surface runoff [31,32,33]. Few studies have evaluated them in terms of water resource recycling.
This study focused on approaches for using permeable pavement as a rainwater collection and recycling system. The objective of this study is to develop a set of permeable pavement water recycling systems that stores infiltrated water in the base and subbase of the pavement. To improve the feasibility of implementing the permeable pavement water recycling system, we utilized the median divider island between roads and the soil within the dividers to transfer water to plants growing in the dividers via capillary action. This study examined capillary rise heights across different soil compaction levels, providing a foundational exploration that informs the future research and design of rainwater collection and recycling systems for permeable pavements. Its findings are valuable for advancing sustainable water management practices in urban environments.

2. Permeable Pavement Water Resource Recycling System Model

The permeable pavement water resource recycling system used in this study is similar to bioretention systems or rain gardens. Bioretention systems first appeared in the 1990s, when they were introduced in Prince George County of Maryland, USA by developers who began to incorporate them into residential developments [34,35,36]. The bioretention systems consisted of a vegetated, artificial basin, which served to clean incoming runoff and allowed it to infiltrate into the soil [37]. It was a Low Impact Development method. Figure 1 shows the profile of a typical bioretention system, which consists of a permeable mulch layer, a soil filtration media, and a gravel layer inlaid with underdrains. During dry periods, the bioretention system works as part of the landscaping. During floods, the bioretention system works to retain and slow runoff, and filtered water that percolates to the underdrains is released. The design emphasis utilizes temporary storage of rainfall runoff to mitigate polluted runoff into the environment [36].
Unlike a bioretention system, the permeable pavement water resource recycling system designed in this study places particular emphasis on long-term storage, recycling and reuse of rainwater. This system primarily uses the permeable pavement to transfer rainfall from the pavement surface to the underlying base and subbase layers where it can infiltrate and contribute to storage. Soil capillary action then transfers water to the upper soil layers where it can be evaporated or transpired by plants, and thus contribute to microclimate water cycles. In addition to the roadway surface, sidewalks can also be incorporated into the water resource recycling system by utilizing permeable interlocking concrete or permeable brick, overlaid on any subsurface material that can store water.
Permeable pavement water resource recycling systems can reduce the need for watering, thus ameliorating the need for specialized water trucks, reducing traffic jams associated with the water truck and reducing water consumption. Also, during extreme precipitation events, the permeable pavement can act as a flood buffer because surface runoff on the road surface will only occur until the water storage volume within and under the permeable pavement is filled. Like traditional roads, ditches on the sides of a permeable pavement road transfer surface runoff and prevent flooding of the road [30]. Permeable pavements can also reduce air and water pollution. During dry periods, air pollutants can settle on the pavement surface. On a pervious pavement, those pollutants are transported through the pavement, where they are then filtered by both the pavement and the underlying materials. The filtering action of bioretention systems reduces both air and water pollution while enhancing system functionality [38,39]. Research indicates a positive linear correlation between the thickness of the gravel layer and the efficiency of removing total suspended solids (TSS) and total phosphorus (TP) from runoff in permeable pavement systems [39].
Additionally, bioretention systems are typically constructed as a vegetated depression or basin [34,35,36], where the storage capacity of the depression is limited by its size. These systems are short-duration retention systems, and once the rain is collected, it slowly infiltrates into the soil. Physically, the primary purpose of the soil is to act as a filter and cleanse the water of pollutants. In addition, chemical or biologic treatments may be used to remove pollutants before the water is allowed to infiltrate into the soil and drain via the underdrains. A bioretention system typically includes an overflow pipe, which allows inflow rates that exceed the outflow rate of the system, to flow out through an underdrain, as shown in Figure 1. In contrast, the permeable pavement water resource recycling system proposed in this study uses the basal layer under the road surface. Water retained in this layer is stored for a relatively long period. Additionally, any water stored underneath the permeable pavement can evaporate through the permeable pavement, helping to reduce the road surface temperature and urban heat island effects [25]. If inflow exceeds the capacity of the road, overflow is directed to a ditch along the side of the road [30]. This design approach emphasizes the reuse of water, which differs from the bioretention system, which simply releases the water rather than attempting to retain it for other uses.
Table 1 compares the water resource recycling capabilities of bioretention and permeable pavement systems. As previously discussed, permeable pavement water resource recycling systems are distinguished by their substantial capacity for long-term water storage and their efficient reuse of rainwater runoff, setting them apart from bioretention systems. These attributes underscore their pivotal role in sustainable urban environments. Both bioretention and permeable pavement water resource recycling systems play essential roles in bolstering urban sustainability. They actively contribute to flood mitigation, filtration of water pollutants, effective management of drainage systems, and the mitigation of urban heat islands. Integrating permeable pavement water resource recycling systems into urban planning and design initiatives is crucial not only for enhancing environmental sustainability but also for fortifying urban resilience amidst the ongoing challenges posed by climate change.
The permeable pavement system used in this study is illustrated in Figure 2. The infiltration layer, or surface layer, can consist of permeable materials such as porous asphalt, pervious concrete, permeable interlocking concrete, or permeable brick. Any water that infiltrates through the pavement is stored in a highly porous gravel grading layer beneath the permeable pavement. The porosity of the porous gravel grading layer determines its water storage capacity. Permeable pavements commonly employ open-graded aggregates to enhance both structural integrity and hydraulic capacity. These aggregates should possess hardness, durability, and a minimal fine particle content passing through the 75 µm sieve size. Select durable, crushed aggregate materials to maximize structural capacity and porosity for water storage. For heavier traffic conditions, a cement- or asphalt-stabilized open-graded aggregate may be more appropriate. Dense-graded aggregates, typically used for road bases, are generally avoided due to their limited water storage capacity and fines that can weaken them when saturated [30]. An impermeable, sloped layer, placed below the bottom of the gravel, prevents the stored water from infiltrating into and reducing the strength of the subgrade soil. The impermeable layer can also be constructed from geomembranes, which have a high tensile strength and are resistant to wear and chemical corrosion and can improve the bearing capacity of the road surface. In other cases, geomembranes may enclose the sides and bottom to create a no infiltration design for water storage and flow control [30]. Also, if a box culvert is constructed in the median divider island, the impermeable layer can be sloped toward the box to store water. It should be noted that the size of the box culvert would be specified based on predicted precipitation associated with climate change.
Figure 2 presents the hydrological cycle process of the permeable pavement water resource recycling system developed in this study. The system emphasizes long-term storage, recycling, and reuse of rainwater. The system utilizes permeable pavement to channel rainfall from the surface to the underlying base and subbase layers. Subsequently, water is directed from these layers toward a planter box situated in the median divider island or a box culvert beneath it. Once runoff reaches the bottom of the planter box or box culvert, it becomes accessible to plants through soil capillary action. Through evaporation or transpiration, the water returns to the atmosphere, thereby integrating into the localized microclimate water cycles.

3. Materials and Methods

3.1. Rainfall and Runoff in Pingtung Area

Pingtung County, situated in southern Taiwan, covers a total area of approximately 2775 km2, ranking as the fifth largest county in Taiwan by land area. The western region features the relatively flat Pingtung Plain, contrasting sharply with the eastern part characterized by undulating hills and towering mountains, some exceeding 3000 m above sea level. Geographically, the entire county lies south of the Tropic of Cancer, experiencing a tropical monsoon climate marked by stable temperatures year-round. Average temperatures range from 22 to 29 °C, with summer peaks soaring to 35 °C and winter lows hovering around 15 °C.
Pingtung County records an annual average rainfall between 1500 and 3000 mm (Figure 3), showing a gradual decline over the past decade. Precipitation varies monthly, with the highest levels occurring in the summer months, particularly during the typhoon season spanning July to September. During these peak months, monthly rainfall can surge to as high as 500 mm (Figure 4).
To understand the impact of rainfall on surface runoff before and after road development, this study used rainfall data from Typhoon Koinu in 2023 for runoff analysis. Rainfall data collected from the Hengchun rain gauge station during Typhoon Koinu are depicted in Figure 5. The maximum rainfall intensity observed was 31 mm, with a cumulative rainfall accumulation of 222 mm recorded over a 24 h period spanning from 4 October 2023, to 5 October 2023. The runoff analysis was conducted using the SCS-CN Method, developed by the United States Soil Conservation Service (SCS) for estimating rainfall–runoff relationships [40]. The analyzed parameters are shown in Table 2.
In Table 2, the SCS Curve Number (CN) is a parameter utilized for estimating rainfall-induced runoff. Variations in CN values among different land covers reflect their respective permeability and water retention capabilities. Imperv (Imperviousness) denotes the fraction of a surface that is impermeable, impeding water infiltration. N-Imperv (Manning’s n for Impervious Surface) quantifies the Manning roughness coefficient, defining flow resistance on impermeable surfaces. N-Perv (Manning’s n for Pervious Surface) quantifies the Manning roughness coefficient, defining flow resistance on permeable surfaces. Width denotes the lateral extent of the flow path, reflecting the width of the road, and is pivotal in determining the length of the runoff pathway. The Drainage Area denotes the catchment area, illustrating the land area draining toward a specific land cover type.
The runoff analysis results are depicted in Figure 6 and Figure 7. Figure 6 depicts the hydrograph detailing runoff characteristics. As illustrated therein, peak runoff instances were observed at the 5th, 10th, and 15th hours. It is noteworthy that these peak occurrences exhibited a delay of one hour relative to the peaks in rainfall intensity observed in Figure 5. Surface runoff peaks on impervious surfaces after development were 1.5 to 4 times higher than those on bare ground. However, through the use of permeable pavement, surface runoff could be restored to pre-development conditions.
Figure 7 depicts the cumulative surface runoff over time. The data reveal that after 5 h of rainfall, bare ground accumulated only 15 m3 of runoff. In contrast, impervious pavement surfaces accumulated 140 m3 of runoff by this time, while pervious pavement surfaces accumulated 65 m3. Pervious pavement reduced runoff by 54% compared to impervious surfaces, highlighting the efficacy of pervious pavement. By the 24th hour of rainfall, cumulative surface runoff on bare ground reached approximately 900 m3, whereas impervious pavement surfaces accumulated about 1200 m3 of runoff. Pervious pavement surfaces accumulated runoff similar to bare ground, around 900 m3, resulting in a 25% reduction in runoff compared to impervious pavement. These observations are consistent with the findings reported in the existing literature, illustrating the tangible benefits of pervious pavement in mitigating runoff impacts compared to traditional impervious surfaces [23,24,25].

3.2. Experiments with a Small-Scale 3D Model of the Permeable Pavement Water Resource Recycling System

The software SketchUp (23.0.418) was used to create a 3D model of the proposed permeable pavement water resource recycling system, as shown in Figure 8. A 3D printer was then used to create a small-scale, physical model (length 300 mm, width 80 mm, height 75 mm). The model has three parts: the foundation layer, the pavement surface layer and the median island separating the two roads. The pavement surface layer was used to simulate permeable pavements, with a thickness of 5 mm. This surface layer contains pores, enabling it to function as a permeable pavement. Water permeates through these pores into the underlying foundation layer, which serves as the water storage space below. During the capillary rise test, it is crucial to maintain adequate water levels in the storage space below the pavement surface layer.
We placed a miniature planter box in the median island, representing the box that would be placed for a tree or other plants. The dimensions of the planter box were 70 mm, width of 40 mm and height of 45 mm, as shown in Figure 9. The bottom of the planter box is permeable, so that the water coming from the basial layer and at the bottom of median divider island can rise via capillary action and be accessible to the plant roots. This design differs from the traditional plantar boxes commonly used in the median divider island, which are generally impermeable, concrete boxes that restrict water movement from the basal layer to the planter box (Figure 10).
The small-scale model was used to evaluate if the water stored at the base of the median divider island can pass through the bottom of the planter box and reach the roots of the plants via capillary action. Using common soils from the Pingtung area in Taiwan, capillary rise experiments were conducted. The soil was sieved with a #30 sieve to remove non-soil debris. Soil characteristics are listed in Table 3. Using the Unified Soil Classification System (USCS), the soil was classified as ML (silt with low plasticity).
The soil was compacted into the small-scale model as follows (Figure 11). The soil was sprayed with water to a moisture content equal to the optimal moisture content of 24%. The soil was then placed in a Ziplock bag for one day to equilibrate the moisture content, and then the soil was compacted to a relative compaction of 80% and 90% in the small-scale planter box, placed in the middle of the median divider island. After compacting the soil into the planter box and injecting water from the surface of the model, the soil moisture content every hour was measured at 5 mm intervals along the planter box height. From these results, the height of capillary rise was evaluated.

3.3. Soil Column Experiments

The design relies on capillary action to permit water to travel from the base of the planter box up to the rooting level of the vegetation. Capillary rise (h) can be approximated as [41]:
h = 4 σ cos θ γ w d
where σ is the surface tension of the fluid, θ is the contact angle between the fluid and the solid surface, γd is the unit weight of the fluid and d is the diameter of a typical pore in the soil.
The limited size of the small-scale 3D model experiment did not permit long-duration evaluation of the capillary action in the planter box. A separate experiment was employed using soil columns. A soil column was composed of 10 acrylic cylinders with an inner diameter of 5 cm and a height of 5 cm. Three different soil columns with height of 50 cm and varying relative compaction (80%, 85% and 90%) were set up. Before compaction, the soil was adjusted to the optimal water content and each layer of 5 cm was equally compacted. From this range of relative compaction, the role of compaction on capillary rise was explored. The soil columns were placed in a shallow pool of water and openings at the bottom of the soil column allowed water to enter the soil columns, as shown in Figure 12 and Figure 13. After sitting for 3 days, the water content at 5 cm intervals long the soil column was measured to determine the capillary rise height.

4. Results and Discussion

4.1. Small-Scale 3D Model Results

In water resource management research, soil capillary rise experiments are widely used to assess soil moisture dynamics under different relative compaction levels [42,43]. These studies not only contribute to understanding the distribution and variation of moisture in urban green spaces but also provide valuable guidance for urban planning and sustainable development.
Moisture content relative to height in the small-scale planter box, for different relative compaction levels and time, is plotted in Figure 14, Figure 15, Figure 16 and Figure 17. Results of the 80% relative compaction level are shown in Figure 14 and Figure 15. From Figure 14, it is evident that the moisture content increased significantly at different heights compared to the initial water content of 24% after water was injected from the surface of the model, particularly closer to the bottom. From the figure, it is evident that the soil moisture near the bottom quickly reached saturation, resulting in minimal differences in moisture content after 1, 2 and 3 h. In contrast, the soil moisture at the top increased more gradually, with noticeable changes over time, as depicted further in Figure 15. Figure 15 illustrates the temporal variation in moisture content at depths of 0.5 cm (bottom) and 4.5 cm (top) of the small-scale model. At the 0.5 cm height, the moisture content was 36.1%, 36.6% and 36.4% after 1, 2 and 3 h, respectively. At the 4.5 cm height, after 3 h, the moisture content rose from 28.3% to 30.4%.
Results of the 90% relative compaction level are shown in Figure 16 and Figure 17. Figure 16 shows that after injecting water from the surface of the model, moisture content increased in the base of the model but changed very little at the top. At the 0.5 cm height, the moisture content was 30.8%, 31.3% and 32.3% after 1, 2 and 3 h, respectively (Figure 17). The soil did not reach the full saturation moisture content of 33.8%. At the 4.5 cm height, after 3 h, the moisture content changed from 24.3% to 24.5%. There was no significant change in moisture content compared to the initial level of 24%. In other words, the capillary rise height under the 90% relative compaction level was less than 4.5 cm. From these results, it can be inferred that at an 80% relative compaction level, the soil at the base of the model can reach saturation and the moisture content at the top of the model will be higher than the moisture content of soil at a 90% relative compaction level.
The experiments conducted using small-scale 3D model tests have revealed that soil capillary rise behavior is notably influenced by varying levels of soil compaction. Specifically, under an 80% relative compaction level, the soil quickly reached saturation at the bottom and displayed minimal changes over time as it approached its maximum water-holding capacity. In contrast, at a 90% relative compaction level, minimal variation in soil moisture content occurred at the surface due to restricted upward movement of moisture from the lower soil layers, thereby maintaining the initial moisture levels. The impact of compaction on moisture dynamics is graphically depicted in Figure 18, where increasing relative compaction levels correlated with decreasing moisture content associated with capillary rise. Conversely, decreasing soil compaction levels corresponded to increasing capillary rise heights, aligning closely with established findings in the literature [44].

4.2. Soil Column Results

Figure 19 shows the moisture content versus relative compaction level of the soil column following placement of the soil column into the pool for 3 days. In the 90% relative compaction soil column, all soil above a height of 15 cm had a moisture content slightly below the initial moisture content of 24%, with the largest deficit near the top of the soil column. This result is a consequence of evaporation and gravitational downward movement of the soil water. The moisture content at 10 cm, 5 cm and 0 cm heights was 27.7%, 30.2%, and 33.8%, respectively. From this result, it is clear that in soil that is compacted at a relative compaction of 90%, the capillary rise does not exceed 15 cm. The soil above 15 cm remained close to the initial moisture content. In summary, at a relative compaction of 90%, the capillary rise is roughly 10–15 cm. In the 85% relative compaction soil column, after 3 days of placement in the pool, the capillary rise was roughly 25 cm to 30 cm. In the 80% relative compaction sample, the capillary rise was 45 cm to 50 cm. These results show that as the relative compaction level increases, the capillary rise reduces. These results are consistent with those obtained from the small-scale 3D model experiments. Moreover, this observation implies that the diameter of the soil column does not influence the soil capillary rise behavior, which indirectly elucidates why the majority of studies employ soil columns with diameters smaller than 5 cm [44]. While the size effect does not affect soil capillary rise behavior, future tests should involve large-scale models or a full-scale permeable pavement water recycling system to validate the system’s feasibility.
Full scale median island planter boxes are at least 60 cm deep. A capillary rise of 45 cm to 50 cm will reach the roots of the plants. As long as the soil moisture content is greater than the permanent wilting point of the plants, the plants will have access to the water and grow. Given the above findings, by controlling the relative compaction level of the soil placed in the planter box and selecting plants with an appropriate rooting depth, capillary rise can be used as a natural watering mechanism, reduce the need for manual watering, and achieve the goal of recycling rainfall runoff.

5. Conclusions

The permeable pavement water recycling system developed in this study utilized a Low Impact Development concept. The system not only reduces flood peaks and purifies rainwater runoff, similar to a bioretention system, but also recycles and reuses rainwater. A small-scale model and a soil column experiment were used to test the feasibility of the proposed design. The results showed that soil water content, naturally sourced from capillary action and water at the base of the planter box, will vary depending on the soil compaction level. The capillary rise in soil at 80% relative compaction was much higher than that of soil at 90% relative compaction. The results of the soil column tests aligned with the findings from the small-scale 3D model experiments. The capillary rise height of the soil increased as the relative compaction level of the soil decreased. If the soil placed in the planter box of the median divider island is at the appropriate compaction, water in the box culvert or at the bottom of the planter box will rise into the top of the planter box and the plants within the box will have access to the water. Therefore, through in-depth investigation into the mechanisms of soil capillary rise behavior and its response to compaction levels, we can better design and manage urban green spaces. This enables the achievement of sustainable urban development goals, enhancing residents’ quality of life and the health of urban ecosystems.
These study results demonstrate the feasibility of the proposed design and show that permeable pavement water resource recycling systems are in line with the Sustainable Development Goals (SDGs). The proposed design will help conserve and protect water resources and help with sustainable water resource management (SDGs 6). It will also help mitigate the impacts of climate change (SDGFs 12). The conceptual framework of the permeable pavement water resource recycling system introduced in this study has successfully determined the capillary rise capabilities of soils at varying compaction levels, thereby providing initial validation of the system’s feasibility. Future investigations should focus on evaluating the viability of plant species commonly found in roadside environments to thrive exclusively through soil capillary action without supplementary irrigation. This additional research will strengthen the system’s practicality and underscore its potential for sustainable water management in urban settings. It is recommended that future tests include large-scale models or a full-scale permeable pavement water recycling system to further confirm its feasibility.

Author Contributions

Conceptualization, S.-R.Y.; Methodology, S.-R.Y.; Software, X.-R.C.; Formal analysis, H.-X.H.; Investigation, H.-X.H.; Writing—original draft, S.-R.Y.; Writing—review & editing, H.-F.Y.; Visualization, H.-F.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Science and Technology Council, grant number [113-NU-E-020-001-NU].

Data Availability Statement

Data is contained within the article.

Acknowledgments

The authors are grateful for the support from the Research Project of the National Science and Technology Council (NSTC) of the Republic of China, Taiwan (113-NU-E-020-001-NU).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Illustration of a typical bioretention system.
Figure 1. Illustration of a typical bioretention system.
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Figure 2. Illustration of the permeable pavement water recycling system.
Figure 2. Illustration of the permeable pavement water recycling system.
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Figure 3. Annual rainfall in Pingtung area from 2009 to 2023.
Figure 3. Annual rainfall in Pingtung area from 2009 to 2023.
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Figure 4. Monthly rainfall in Pingtung area from 2009 to 2023.
Figure 4. Monthly rainfall in Pingtung area from 2009 to 2023.
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Figure 5. Hourly rainfall data for Typhoon Koinu in 2023.
Figure 5. Hourly rainfall data for Typhoon Koinu in 2023.
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Figure 6. Analysis results of rainfall runoff from Typhoon Koinu in 2023.
Figure 6. Analysis results of rainfall runoff from Typhoon Koinu in 2023.
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Figure 7. Accumulated runoff volume of Typhoon Koinu in 2023.
Figure 7. Accumulated runoff volume of Typhoon Koinu in 2023.
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Figure 8. Small-scale model design drawing.
Figure 8. Small-scale model design drawing.
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Figure 9. Permeable planter box placed in the median divider island.
Figure 9. Permeable planter box placed in the median divider island.
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Figure 10. Typical concrete planter boxes used in a median divider island.
Figure 10. Typical concrete planter boxes used in a median divider island.
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Figure 11. Example of how soil was placed into the miniature planter box at the center of the permeable pavement model.
Figure 11. Example of how soil was placed into the miniature planter box at the center of the permeable pavement model.
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Figure 12. Capillary rise experimental setup.
Figure 12. Capillary rise experimental setup.
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Figure 13. Photo of capillary rise experimental setup.
Figure 13. Photo of capillary rise experimental setup.
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Figure 14. Moisture content relative to height (80% compaction).
Figure 14. Moisture content relative to height (80% compaction).
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Figure 15. Moisture content at 0.5 and 4.5 cm versus time (80% compaction).
Figure 15. Moisture content at 0.5 and 4.5 cm versus time (80% compaction).
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Figure 16. Moisture content relative to height (90% compaction).
Figure 16. Moisture content relative to height (90% compaction).
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Figure 17. Moisture content at 0.5 and 4.5 cm versus time (90% compaction).
Figure 17. Moisture content at 0.5 and 4.5 cm versus time (90% compaction).
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Figure 18. Effect of relative compaction on moisture content.
Figure 18. Effect of relative compaction on moisture content.
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Figure 19. Soil column height versus moisture content relative to soil compaction.
Figure 19. Soil column height versus moisture content relative to soil compaction.
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Table 1. Comparison of bioretention and permeable pavement water resource recycling system capabilities.
Table 1. Comparison of bioretention and permeable pavement water resource recycling system capabilities.
SystemTypeFlood ProtectionLong-Duration Water StorageWater FiltrationReuse of Rainfall RunoffDrainageReduces Heat Island Effect
Bioretention system✓✗✓✗✓✓
Permeable pavement Water resource Recycling system✓✓✓✓✓✓
Table 2. The analyzed parameters for runoff analysis conducted using the SCS-CN method.
Table 2. The analyzed parameters for runoff analysis conducted using the SCS-CN method.
Bare GroundImpermeable Asphalt ConcretePermeable Pavement
SCS(CN)878960
Imperv210015
N-Imperv0.050.0110.011
N-Perv0.050.0120.011
Width (m)101010
Drainage Area (ha)111
Slope (%)111
Table 3. Soil physical properties used in this study.
Table 3. Soil physical properties used in this study.
Soil PropertiesAnalysis Results
Specific gravity of soil solids, Gs2.65
Liquid limit, LL (%)30
Plastic limit, PL (%)26
Plasticity index, PI (%)4
Optimum moisture content, OMC (%)24
Maximum dry unit weight, γdmax (g/cm3)1.55
Soil classificationML
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MDPI and ACS Style

Yang, S.-R.; Chen, X.-R.; Huang, H.-X.; Yeh, H.-F. Innovation in Water Management: Designing a Recyclable Water Resource System with Permeable Pavement. Water 2024, 16, 2109. https://doi.org/10.3390/w16152109

AMA Style

Yang S-R, Chen X-R, Huang H-X, Yeh H-F. Innovation in Water Management: Designing a Recyclable Water Resource System with Permeable Pavement. Water. 2024; 16(15):2109. https://doi.org/10.3390/w16152109

Chicago/Turabian Style

Yang, Shu-Rong, Xing-Rong Chen, Hao-Xuan Huang, and Hsin-Fu Yeh. 2024. "Innovation in Water Management: Designing a Recyclable Water Resource System with Permeable Pavement" Water 16, no. 15: 2109. https://doi.org/10.3390/w16152109

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