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Review

Assessment of the Hydrological Performance of Grass Swales for Urban Stormwater Management: A Bibliometric Review from 2000 to 2023

1
College of Architecture and Urban Planning, Guangzhou University, Guangzhou 510006, China
2
Architectural Design and Research Institute of Guangzhou University, Guangzhou 510091, China
3
Art School, Hunan University of Information Technology, Changsha 410151, China
*
Authors to whom correspondence should be addressed.
Water 2025, 17(10), 1425; https://doi.org/10.3390/w17101425
Submission received: 28 March 2025 / Revised: 5 May 2025 / Accepted: 6 May 2025 / Published: 9 May 2025

Abstract

:
Grass swales have emerged as a cost-effective and sustainable stormwater management solution, addressing the increasing challenges of urbanization, flooding, and water pollution. This study conducted a bibliometric analysis of 224 publications to assess research trends, key contributors, and knowledge gaps in grass swale applications. Findings highlighted the growing emphasis on optimizing hydrological performance, particularly in response to intensifying climate change and urban flood risks. Experimental and simulation-based studies have demonstrated that grass swale efficiency is influenced by multiple design factors, including vegetation type, substrate composition, hydraulic retention time, and slope gradient. Notably, pollutant removal efficiency varies significantly, with total suspended solids (TSS) reduced by 34.09–89.90%, chemical oxygen demand (COD) by 7.75–56.71%, and total nitrogen (TN) by 32.37–56.71%. Additionally, studies utilizing the Storm Water Management Model (SWMM) and TRAVA models have demonstrated that integrating grass swales into urban drainage systems can result in a 17% reduction in total runoff volume and peak flow attenuation. Despite these advancements, key research gaps remain, including cost-effective design strategies, long-term maintenance protocols, and integration with other green infrastructure systems. Future research should focus on developing innovative, low-cost swale designs, refining optimal vegetation selection, and assessing seasonal variations in performance. Addressing these challenges will enhance the scientific foundation for grass swale implementation, ensuring their sustainable integration into climate-resilient urban planning.

1. Introduction

With the rapid advancement of urbanization, vast areas of cultivated land, grasslands, and woodlands have been replaced by impermeable surfaces such as cement and asphalt [1,2]. This transformation significantly reduces natural infiltration capacity, leading to an expansion of hardened surfaces, including rooftops and paved grounds. As a result, stormwater runoff accelerates, shortening its formation time while increasing runoff volume, intensity, and peak discharge [3]. This shift disrupts the natural urban hydrological cycle, exacerbating flood risks and contributing to severe urban waterlogging [4]. Moreover, as stormwater runoff travels across rooftops and road surfaces, it mobilizes various pollutants, including suspended solids, heavy metals, nutrients, toxic organic compounds, and pathogenic microorganisms [5]. These contaminants are transported into receiving water bodies, leading to significant deterioration in urban water quality. Such pollution poses substantial threats to aquatic ecosystems and public health, necessitating advanced stormwater management strategies to mitigate these adverse impacts [6,7].
To address these challenges, numerous countries have introduced advanced stormwater management strategies and technologies. The United Kingdom developed the Sustainable Urban Drainage System (SUDS) [8,9], while the United States implemented Best Management Practices (BMPs) [10] and Low Impact Development (LID) [11]. Similarly, Australia adopted Water Sensitive Urban Design (WSUD), and China initiated the Sponge City concept to enhance urban flood resilience [12]. BMPs integrate natural and engineered urban elements, including green spaces, public plazas, rooftops, and permeable surfaces, to regulate rainwater dynamics [13,14]. Key interventions such as bioretention basins, green roofs, grass swales, and permeable pavements play a crucial role in attenuating peak runoff, delaying peak discharge, and improving water quality [15]. LID, which emerged in the 1990s, emphasizes Source Control and the establishment of efficient hydrological circulation systems [16,17]. It aims to minimize total runoff through infiltration, filtration, and on-site water storage, ensuring that the hydrological function of urbanized areas remains as close as possible to their natural state [18,19]. Despite these advancements, conventional drainage infrastructure, typically comprising side ditches, rainwater outlets, connecting conduits, and municipal pipelines, continues to be widely utilized [20]. Early stormwater management primarily relied on detention storage tanks to mitigate peak runoff. However, while these facilities reduced immediate flooding risks, they failed to significantly lower total runoff volumes [21]. Additionally, prolonged water stagnation in these systems often led to pollutant accumulation, exacerbating urban water quality issues [22,23].
A grass swale is a shallow, vegetated channel designed to facilitate the infiltration, retention, and purification of stormwater while also contributing to the urban landscape [24,25]. As an open drainage system, it effectively manages surface runoff by filtering pollutants and reducing peak flow rates. Grass swales are also referred to as vegetated shallow ditches, biological swales, or shallow grass channels, depending on their specific design and function [26]. As a fundamental component of BMPs, grass swales are widely implemented in residential, commercial, and industrial areas. They are typically installed along roadways, within large green spaces, or adjacent to impermeable surfaces to facilitate stormwater collection and runoff regulation [27]. In some cases, grass swales can function as an alternative to conventional stormwater pipe networks or be integrated into larger drainage systems for enhanced efficiency [28]. Compared to traditional stormwater management infrastructure, grass swales offer cost-effectiveness, simplicity, and ease of maintenance. As a core element of LID strategies, they provide a natural drainage solution that can reduce investment costs by nearly 50%, making them a sustainable and economically viable option for urban flood management [29].
Grass swales can be classified into three primary types based on their surface runoff transmission characteristics: standard transmission grass swales, dry grass swales, and wet grass swales [30]. Standard transmission grass swales are primarily utilized for stormwater conveyance and preliminary treatment, featuring a relatively simple structural design. Dry grass swales, in contrast, incorporate a subsurface drainage system within their structural composition. This system typically includes a high-permeability filter medium that enhances infiltration capacity and improves overall hydrological performance [31]. Wet grass swales, by design, maintain a consistently saturated state, allowing for prolonged water retention and enhanced pollutant removal efficiency. The hydrological performance of a grass swale is influenced by several key design parameters, including swale length, height, cross-sectional shape, slope gradient, flow velocity, Manning’s roughness coefficient, and vegetation type and height. These factors collectively determine the swale’s runoff regulation and pollutant removal efficiency [32]. For instance, the length and flow velocity directly impact pollutant filtration, while an optimal flow speed is crucial for preserving the integrity of the swale’s surface soil and vegetation [33]. Additionally, the slope gradient governs runoff conveyance and infiltration dynamics, affecting the overall hydraulic efficiency of the system. Consequently, a well-engineered design is essential for optimizing stormwater management performance, ensuring effective runoff control and water quality enhancement [34].
The ubiquitous implementation of green drainage infrastructures in urban landscapes has precipitated a marked interest in the functionality and efficacy of grass swales within the domain of urban stormwater management. Rey-Mahia et al. [35] devised a laboratory model that integrated elements of ground-source heat pumps to appraise the thermal performance of grass swales. Their findings corroborated the hypothesis that grass swales maintain robust resilience under diverse temperature regimes, thereby positing them as viable, energy-efficient, and multifunctional infrastructures. Chen et al. [36] utilized bibliometric methods to review the research on grass swales, highlighting their advantages in hydrological control, water quality purification, and biodiversity enhancement. Gavric et al. [37] synthesized the processes by which grass swales improve urban rainwater quality, discussing and summarizing empirical studies on their water purification capabilities. This work identified key variables influencing the enhancement of rainwater quality and emphasized their role in mitigating road runoff pollution. A literature review involves the meticulous processing of vast amounts of data, analyzing theoretical frameworks, research methodologies, and findings to support more comprehensive investigations. Undertaking a comprehensive review of the literature on grassed swales not only facilitates a nuanced understanding of the current research landscape but also identifies emergent trends and fosters future innovations in this field [38].
Grass swales have emerged as one of the most widely implemented and effective stormwater management solutions across numerous countries. Extensive research has been conducted on their hydrological functions, yet comprehensive hydrological performance assessments in the context of urban flood management remain limited. This study consolidates global research on the hydrological performance of grass swales through bibliometric methods, aiming to elucidate research advancements and knowledge gaps in the domains of hydrological mechanisms analysis, design optimization, and functional enhancement. It provides a multidimensional evidence base to support the core objectives of analyzing hydrological control mechanisms, optimizing design configurations, and improving the overall functionality of vegetated swales. The findings offer practical guidance for their application by refining parameter selection and performance criteria, thereby ensuring more effective integration into urban flood mitigation strategies. This study advances the role of grass swales in mitigating urban waterlogging, reducing non-point source pollution, and restoring urban hydrological cycles. It provides knowledge-mapping support for optimizing high-density urban resilient stormwater management systems, while establishing a scientifically robust framework with both theoretical depth and practical guidance for precision design, region-specific adaptive management, and the policy governance of grass swales. These findings hold critical implications for advancing Sponge City initiatives, promoting sustainable development, and bridging technological gaps in green infrastructure implementation.

2. Materials and Methods

2.1. Literature Search

The literature review was conducted using the Web of Science Core Collection, a globally recognized citation database encompassing over 18,000 high-impact journals, 180,000 conference proceedings, and 80,000 scholarly books. This database was selected due to its multidisciplinary coverage and reliability in academic research. A systematic search was performed to identify relevant publications on grass swales in the context of urban stormwater management. The search included English-language articles with titles, abstracts, or keywords containing the terms: “grass ditch”, “grass swale*”, “dry swale*”, “wet swale*”, and “vegetative swale*”. To ensure comprehensive search results, a truncated search using the wildcard asterisk (*) was implemented during the retrieval process. The time frame for the search was limited to 2000–2023, yielding an initial dataset of 263 articles. To refine the dataset, a manual screening process was conducted by reviewing article titles and abstracts. Studies unrelated to urban stormwater management were excluded. For instance, some results related to “grass swale*” examined discontinuous gullies caused by bank erosion in tropical sand-bed streams, which were deemed outside the scope of this study. After filtering out irrelevant records, a total of 224 publications were retained for analysis. These selected articles primarily focused on the hydrological functions of grass swales, including their role in runoff regulation, pollutant removal, and stormwater mitigation in urban environments.

2.2. Data Processing

This study employed CiteSpace, a software specifically designed for scientometric analysis and data visualization [39]. CiteSpace enables the exploration of scientific knowledge structures, revealing research trends, key contributors, and thematic advancements within a given field. The software is compatible with multiple databases, facilitating a comprehensive quantitative assessment of the literature. The 224 articles (2000–2023) were utilized as the original dataset for CiteSpace knowledge mapping analysis. Using bibliometric methods, we conducted systematic investigations into this dataset, including co-citation analysis, keyword clustering, and timeline evolution. These analyses formed the empirical foundation for the core conclusions of this paper and are visualized through knowledge maps and other graphical representations. The references listed at the end of the paper comprise supporting the literature directly cited in the main text, as well as the pivotal literature that engage directly with the research hypotheses, methodology, and conclusions.
To evaluate academic influence and knowledge structure, the G-index was utilized as a key bibliometric indicator. First proposed by Leo Egghe in 2006, the G-index quantifies scholarly impact by controlling the density of network visualizations [40]. Within CiteSpace, the G-index threshold was adjusted through a scale factor (k-value), which determines the number of nodes displayed in co-citation and collaboration networks. A higher k-value increases the number of nodes, revealing broader connections, whereas a lower k-value refines the analysis by highlighting only the most influential literature. Through iterative testing, an optimal k-value of 15 was selected to ensure that the core structure and intellectual dynamics of the grass swale research were effectively captured.
The bibliometric workflow is summarized in Figure 1, detailing the methodological steps undertaken in CiteSpace (version 6.1). The analytical procedure included: (1) importing the dataset of 224 articles into CiteSpace in text format; (2) defining the study parameters, by setting the analysis period to 2000–2023 with a time slice of one year; (3) analyzing the authorship, national contributions, and publication trends across the 224 articles; (4) categorizing the literature based on the hydrological performance criteria of vegetated swales, identifying 112 studies focused on water quality purification and 166 studies addressing runoff regulation; (5) processing these two article categories separately in CiteSpace to examine national research outputs, co-citation networks, and keyword timeline evolution for each group; (6) visualizing analytical outcomes through knowledge maps and graphical representations, followed by critical discussions and gap analysis of the existing research to identify emerging hotspots; and (7) utilizing CiteSpace’s “burstness” function to detect emerging research trends, examine the evolution of key topics, and predict potential future directions in grass swale research.

3. Results and Discussions

3.1. Hot Topics

3.1.1. Analysis of Publishing Trends

To better analyze the publication trends in research on the role of grass swales in urban stormwater management, 224 articles retrieved from Web of Science and screened were subjected to bibliometric analysis. The results revealed that publications related to the application of vegetated swales in urban stormwater management were disseminated across 103 academic journals. The average citation count per paper was 28.14, while the average number of contributing authors per article was 3.30. As illustrated in Figure 2, the early years of research (2000–2005) saw limited academic output on grass swales in flood management, with an annual publication count not exceeding five. A transient surge in publication volume was observed in 2006, a phenomenon that may correlate with the establishment of the LID concept and the refinement of related research methodologies [41,42].
Notably, 2012 witnessed a marked surge in research publications on grass swales, a trend likely linked to China’s forward-looking policy planning for Sponge City development. Although the formal Sponge City Initiative was announced in 2013 [43], preliminary policy deliberations may have catalyzed academic pre-research on green infrastructure, driving concentrated scholarly output in 2012. This policy, aimed at enhancing urban resilience through nature-based solutions, had a profound influence on the field, resulting in a fourfold increase in publications compared to the previous year. By 2019, the number of articles had surged to 35, underscoring the growing recognition of urban flood management as a critical research priority. A temporary decline in publication rates was observed in 2020, likely attributable to the impacts of the COVID-19 pandemic. The transition to remote work introduced significant challenges for advancing stormwater management and infrastructure research, including budgetary constraints and temporal inefficiencies [44,45]. However, a strong rebound was observed in 2021, with citation counts peaking at 915, the highest recorded to date. This surge reflected the increasing global focus on extreme weather events and urban flooding, driving heightened academic and policy interest in the optimization of grass swales for climate resilience. In 2022 and 2023, researchers identified higher performance limitations in grass swales compared to other green infrastructure systems. This led to a strategic shift in the research focus toward alternative domains of urban stormwater management, consequently diminishing scholarly attention to grass swale studies [46].

3.1.2. Author and Country Analysis

Bibliometric analysis using CiteSpace identified 742 authors from 122 countries contributing to the 224 selected publications on grass swale research. The citation analysis highlighted the ten most influential authors, as summarized in Table 1. Among these scholars, Maria Viklander emerged as the most prolific author, having published seven articles since 2018 [47,48,49]. Other notable contributors include William Frederick Hunt, Sezar Gulbaz, and Cevza Melek Kazezyilmaz-Alhan, each of whom had authored five papers in this domain [50,51,52]. The frequency of co-citations involving these researchers underscored their significant impact on the field. The high publication output and citation frequency of these scholars not only reflected their dedication to advancing grass swale research but also indicated their substantial academic contributions to stormwater management, sustainable urban drainage systems, and climate-resilient infrastructure [53]. Their collective work has played a crucial role in shaping contemporary research trends and expanding the scientific knowledge base in urban hydrology [37].
Table 2 presents the top 10 countries that have made significant academic contributions to grass swale research. The United States and China emerged as the leading contributors, publishing 70 and 56 papers, respectively. Their combined output significantly exceeded that of Australia, which ranked third with 17 publications. This disparity underscored the dominant role of the United States and China in advancing research on grass swales and urban stormwater management. According to database records, the United States not only led in publication volume but also had the earliest recorded research in this field, dating back to 2001. Studies from this country have had a substantial impact, including a simulation-based analysis by Zhang et al. [54], which evaluated the efficiency and potential of pollutant removal in rainfall scenarios. It is noteworthy that the high publication output from the United States and China may stem from sustained long-term research investments, while Iran, though first publishing on this topic in 2019, has already produced eight papers, which could be attributed to a rapidly growing interest in recent years or support from international collaborations.
Figure 3 illustrates the International Cooperation Network, depicting collaborative relationships among countries in grass swale research. In this network, each node represents the number of publications from a specific country, with larger nodes indicating greater contributions. The thickness of the connecting lines denotes the strength of bilateral research collaboration. The figure highlights strong research synergies between the United States and China, as well as their extensive collaborations with multiple other nations. The degree of international research cooperation was closely linked to national policies. The United States, for instance, pioneered the LID concept in the 1990s, which has since influenced global urban stormwater management practices [55]. This early policy initiative has fostered cross-border academic partnerships, reinforcing the United States’ leadership in sustainable drainage research and its collaborative engagements with other research-intensive nations. The collaborative network spans Asia, Europe, North America, and Oceania, demonstrating the globalized nature of research collaboration in this field, with transnational issues such as wetland conservation and climate change mitigation gaining heightened scholarly attention. China holds a pivotal position within this network, serving as a primary initiator and resource contributor, while maintaining multilateral partnerships with European, American, and Asia-Pacific nations [56].

3.2. Study on the Water Quality Purification Performance of Grass Swales

3.2.1. Current Research Status

The expansion of impervious surfaces in urban areas has led to a significant increase in stormwater runoff contamination, posing escalating challenges for urban water management [57]. As stormwater flows over these surfaces, it accumulates pollutants such as heavy metals, suspended solids, nutrients, and organic compounds, contributing to severe water quality degradation. The growing urgency to mitigate these impacts has positioned grass swales as a sustainable, nature-based solution, attracting substantial interest from both academic researchers and policymakers. Systematic screening identified 112 research papers focusing on the water purification performance of grass swales. As depicted in Figure 4, the majority of studies originated from the United States (42 publications; 37.5%), followed by China (24; 21.4%), Australia (11; 9.8%), England (7; 6.2%), and Sweden (6; 5.3%). Most publications primarily analyzed case studies within their respective countries, suggesting that geographical policy frameworks influence research priorities. Interestingly, the volume of research output did not correlate directly with precipitation levels. Instead, policy incentives and environmental regulations appeared to be the key drivers of research activity [58]. Countries experiencing severe water pollution challenges, particularly in Europe, North America, and Asia, have proactively implemented stormwater management policies to enhance urban water quality [59,60]. These initiatives have fueled research efforts and the widespread adoption of grass swales, demonstrating that their prevalence is strongly linked to regulatory frameworks and public support for sustainable water management.
The earliest literature on grass swale research dates back to 1995. As illustrated in Figure 5, the primary research themes in this domain encompass: (1) comprehensive stormwater management approaches, (2) emerging challenges in sustainable drainage systems, (3) surface runoff dynamics, (4) urban stormwater infrastructure, and (5) the systematic reviews of grass swale applications. Studies focusing on the water purification performance of grass swales primarily investigated two key aspects: (1) pollutant removal efficiency and (2) performance optimization in urban rainwater treatment. These investigations assessed the capacity of grass swales to mitigate contaminants such as heavy metals, nutrients, suspended solids, and organic pollutants [61]. Additionally, research evaluated design modifications and operational strategies to enhance hydrological effectiveness, ensuring improved stormwater treatment and urban flood resilience.
Bibliometric analysis of the keyword distributions (Figure 6) indicated that research on the water purification performance of grass swales first appeared in 2000. Over time, the frequency and diversity of relevant keywords have steadily increased, reflecting the growing academic interest in this field. Among the high-frequency terms, “water quality” emerged as the most prevalent, appearing in 40 studies and accounting for 21% of the total keyword occurrences. Numerous studies have reaffirmed that water quality improvement is a key ecosystem service provided by grass swales. Experimental investigations by Yuan et al. [62] demonstrated the efficacy of grass swales in pollutant removal from stormwater runoff. Their findings indicated removal rates ranging from 34.09% to 89.90% for total suspended solids (TSS), 7.75% to 56.71% for chemical oxygen demand (COD), 32.37% to 56.71% for total nitrogen (TN), and 13.33% to 19.67% for total phosphorus (TP). These results underscore the potential of grass swales as a cost-effective, nature-based solution for urban stormwater purification and pollutant reduction.
The design methodology of grass swales is a critical factor influencing their pollutant removal efficiency [63]. Variations in structural configurations significantly impact their capacity for contaminant filtration and water quality enhancement. Research by Stagge et al. [64] evaluated the effectiveness of two distinct grass swale designs for treating highway runoff pollutants. The first design incorporated a pre-treatment system, while the second included a vegetation dam to enhance sediment and heavy metal retention. The study assessed the removal efficiency of TSS and metals such as lead, copper, zinc, and cadmium. Results indicated that for stormwater runoff with TSS concentrations exceeding 30 mg/L, the swales achieved TSS reductions of 41% to 56%, with an additional 1% to 19% decrease following treatment. Comparative analysis revealed that the pre-treated swale design exhibited superior pollutant removal performance. However, the vegetation dam design had a comparatively lower impact on water quality improvement. The study emphasized that grass swales incorporating vegetative barriers, when properly maintained to prevent long-term sediment accumulation and clogging, offer an effective strategy for heavy metal and particulate pollutant removal in urban stormwater runoff.
The influence of vegetation type and substrate composition on the pollutant removal efficiency of grass swales has become a prominent research focus, and a total of 52 relevant literature sources were identified [65,66]. Studies have demonstrated that different vegetation covers and substrate matrices significantly affect the hydrological and decontamination performance of these systems. Leroy et al. [67] conducted a comparative analysis of two vegetated swale designs, one incorporating grassland vegetation and the other featuring larger, deep-rooted plants. The study assessed the removal efficiency of TSS, TP, and total hydrocarbons (THC) from stormwater runoff. Findings indicated that deeper-rooted vegetation exhibited superior performance in retaining soil particles and trapping contaminants, thereby enhancing water quality improvement. Additionally, the pollutant removal efficiency of grass swales varies seasonally. Yuan et al. [62] investigated seasonal fluctuations in purification capacity, revealing that grass swales demonstrated higher water quality improvement in summer compared to winter conditions. These seasonal variations are likely attributed to differences in biological activity, plant growth rates, and microbial degradation processes. Site-specific conditions must also be considered when selecting appropriate swale designs. Certain configurations, such as wet depressions and bio-retention swales, exhibit distinct capabilities for heavy metal and nutrient removal. Research indicates that wet depressions are more effective in nitrogen removal, whereas bio-retention swales provide superior phosphorus and bacterial reduction [68]. Consequently, the optimal design of a grass swale requires comprehensive site assessment that considers local climate conditions, soil characteristics, financial feasibility, and long-term maintenance requirements [69,70]. These factors are essential in maximizing the efficiency and sustainability of grass swale systems in urban stormwater management.
The pollutant removal efficiency of grass swales is intrinsically linked to key design parameters, including surface area, length, depth, cross-sectional shape, slope gradient, and vegetation height. Additional factors such as the presence of dams, hydraulic retention time, roughness coefficient, and soil composition further influence contaminant filtration and stormwater treatment performance [71]. Grass swales primarily facilitate pollutant removal through physical filtration, effectively trapping suspended solids, nutrients, and heavy metals present in stormwater runoff. These systems act as natural biofilters, reducing contaminant loads through sedimentation, adsorption, and infiltration processes [72]. Furthermore, the metabolic activity of vegetation and soil microorganisms enhances biodegradation and nutrient assimilation, contributing to improved water quality and ecosystem resilience [73].

3.2.2. Future Research Directions

Grass swales are increasingly recognized as sustainable, nature-based stormwater management solutions, particularly in high-density urban environments [74]. While existing studies provide comprehensive application guidelines for grassed swales in urban stormwater management, future research must refine design criteria based on localized environmental data. This includes further optimization of the key design parameters to enhance performance across various grass swale configurations [75]. As illustrated in Figure 7, research interest in pollutant removal efficiency has intensified over the past decade, driven by worsening water pollution and rapid urbanization. The water sources addressed by grass swales for pollution mitigation include: surface runoff (non-infiltrating surface water flow generated by rainfall or snowmelt, commonly observed on impervious surfaces such as urban roads, rooftops, and parking lots); first flush rainfall (initial stormwater with elevated pollutant loads from accumulated surface contaminants like dust, oil residues, and heavy metals during the early phase of precipitation); and combined sewage (the overflow mixtures of stormwater and domestic wastewater discharged during heavy rain events in combined sewer systems). The growing emphasis on urban flood resilience underscores the critical role of grass swales in stormwater purification and runoff mitigation. Since 2022, the research focus has shifted from pollutant extraction toward design optimization, reflecting an increasing awareness of grass swales as a key component of green infrastructure [76].
Recent advancements highlight the need for experimental investigations to refine the structural and functional aspects of grass swales. Future studies should prioritize: (1) the development of cost-effective swale designs that enhance pollutant removal efficiency while maintaining economic feasibility [77]; (2) the evaluation of different vegetation types to assess their specific impacts on water quality improvement [78]; and (3) the optimization of design parameters for standard transmission, dry, and wet grass swales, ensuring maximum hydrological and ecological benefits [79].

3.3. Regulating Runoff

3.3.1. Current Research Status

The expansion of impervious surfaces in urban areas has significantly altered natural hydrological cycles, placing greater strain on stormwater management systems. Grass swales have gained widespread attention from both academia and policymakers due to their ability to regulate runoff, mitigate peak flow rates, and enhance urban flood resilience [80]. The effectiveness of grass swales in runoff management is influenced by multiple factors, including swale type, slope gradient, regional climate conditions, antecedent rainfall, subsurface drainage layers, and vegetation composition [81]. Compared to traditional drainage ditches, grass swales offer additional ecological benefits, functioning as artificial ecosystems that support biodiversity and water quality improvement [82,83].
This bibliometric analysis identified 166 studies focused on runoff regulation. As depicted in Figure 8, the majority of these studies were conducted in the United States (59 publications; 35.5%), followed by China (37; 22.2%), South Korea (13; 7.8%), Australia (13; 7.8%), and Sweden (9; 5.4%). The literature review spanned research published between 1996 and 2022, reflecting ongoing advancements in the hydrological performance assessments of grass swales.
As shown in Figure 9, the cited literature clustered into six key research themes, which included: (1) watershed-scale bioretention systems, (2) grass swale hydrological performance, (3) China’s Sponge City initiative, (4) green infrastructure practices, (5) vegetated infiltration swales, and (6) BMP treatment performance. These thematic clusters indicated that grass swale research has evolved from isolated case studies to comprehensive, multi-scalar evaluations, integrating critical aspects such as hydrological modeling and climate adaptations [84].
As depicted in Figure 10, runoff regulation has remained a central focus in grass swale research. The terms “performance” and “runoff” were the most frequently cited keywords, appearing 53 and 37 times, respectively, with the earliest references dating back to 2001. The prevalence of these terms exhibited an upward trajectory, reflecting the increasing importance of hydrological performance assessments in urban stormwater management.
Grass swales play a crucial role in attenuating runoff velocity, thereby reducing erosion potential and mitigating stormwater-induced urban flooding. Their ability to intercept and temporarily retain stormwater minimizes hydraulic stress on drainage infrastructure, making them an effective nature-based solution for flood mitigation [85]. Consequently, the regulation of runoff dynamics by grass swales has continued to attract significant research attention. Since 2019, the application of simulation models to assess swale performance has gained prominence, as indicated by the increasing frequency of “model” as a keyword. Computational hydrological models allow researchers to quantitatively evaluate the efficacy and efficiency of grass swales in runoff regulation under various climatic and urban conditions. Research themes have increasingly centered on design parameters, experimental modeling approaches, and performance evaluation metrics, demonstrating a shift towards the data-driven optimization of swale designs. For instance, Gao et al. [86] employed the Storm Water Management Model (SWMM) to simulate hydrological processes, providing insights into the capacity of grass swales to regulate rainfall runoff under varying environmental conditions. The integration of hydrological modeling tools into grass swale research enhances the predictive accuracy of performance assessments, supporting evidence-based urban water management strategies.

3.3.2. Experimental Simulation

Simulation-based research enables scholars to obtain and analyze hydrological data efficiently, often utilizing computational models to evaluate grass swale performance in runoff regulation. Various modeling approaches serve distinct purposes, including scenario simulation, hydrological calculations, and system optimization. For instance, Abida et al. [87] developed a computer model to analyze and design a porous tube system for stormwater infiltration. During the modeling process, it was essential to consider key design parameters that influence experimental outcomes, such as swale dimensions, substrate permeability, and structural configuration. The simulation model underwent multiple calibration and validation stages, allowing for batch-wise traffic calculations to enhance predictive accuracy. In another study, Xie et al. [88] conducted a hydrological simulation using the SWMM to analyze a village in Jiangsu Province, China. By incorporating the rainstorm intensity equation, different precipitation scenarios were synthesized through the Chicago water level model, facilitating a comparative assessment of flood mitigation strategies. Beyond computational modeling, experimental studies have been instrumental in assessing the hydrological performance of grass swales. Gavric et al. [37] utilized the Rainfall–Watershed–Swale experiment, integrating a controlled laboratory setup to evaluate runoff regulation parameters. Key variables included rainfall intensity, soil composition, grass species, drainage area characteristics, and vegetation height.
In addition to model-based evaluations, controlled field studies have further advanced the understanding of grass swale efficiency. Deletic et al. [89] conducted a comparative study of grass swales in Aberdeen, Scotland, and Brisbane, Australia, using TSS concentration as a performance indicator. The TRAVA model, applied in the study, proved to be a reliable tool for predicting stormwater management performance. Moreover, Winston et al. [90] examined the impact of adding a dam to a grass swale system in a street in the United States. Performance monitoring before and after the modification revealed a 17% reduction in the total runoff volume and a notable decrease in peak flow rates. However, the study also highlighted potential challenges, such as blockage risks, prolonged water retention, and vegetation degradation. Grass swales offer a cost-effective and simple solution for urban stormwater regulation. However, their effectiveness is strongly dependent on regular maintenance, as the frequency of maintenance is directly proportional to runoff regulation efficiency. Proper upkeep is essential to prevent clogging, ensure long-term hydrological functionality, and sustain vegetation health, ultimately enhancing their role in urban flood management.

3.3.3. Future Research Directions

Bibliometric analysis using CiteSpace identified the keyword “sudden” in relation to runoff regulation, indicating that grass swales are widely recognized as an effective measure for mitigating runoff erosion. As illustrated in Figure 11, grass swales play a critical role in urban stormwater management, offering a sustainable solution for controlling runoff and reducing flood risks. In addition to hydrological benefits, the economic feasibility of implementing grass swales in urban flood management requires further investigation. Kim et al. [91] conducted a large-scale study analyzing 447 landscape projects across the United States, assessing the role of various green infrastructure elements, including grass swales, in community development. The findings revealed that nearly 50% of the projects demonstrated significant benefits of the green infrastructure, including economic growth stimulation, improved built environments, and enhanced environmental resilience.
As research on grass swale runoff regulation continues to advance, future studies should focus on: (1) cost-effective and innovative design strategies to enhance runoff management efficiency while ensuring economic viability [92]; (2) optimized operation and maintenance practices to sustain long-term functionality and prevent performance degradation [93,94]; and (3) integration with complementary stormwater management systems, evaluating synergistic effects with other green and gray infrastructure for enhanced flood mitigation and water quality improvement [95].

4. Conclusions

Grass swales have emerged as a widely implemented and effective nature-based solution for urban stormwater management, offering significant benefits in runoff regulation, pollutant removal, and flood mitigation [96]. The bibliometric analysis of 224 publications reveals that current research trends are increasingly focusing on optimizing the structural design of grass swales and evaluating their implementation costs and long-term economic value within urban stormwater management systems. The analysis also identified key contributors in this field, including Maria Viklander from the Swedish Meteorological and Hydrological Institute, William Frederick Hunt at North Carolina State University of United States, and Sezar Gulbaz of Istanbul University. Furthermore, methodologies for assessing the performance of vegetated swales have been continuously refined, including scenario-based simulations of their applications, the real-time monitoring of dynamic responses through sensor networks, and comprehensive life cycle assessments. These findings highlight a growing emphasis on optimizing hydrological performance, particularly in response to increasing urbanization and climate-induced extreme weather events [97,98].
Existing studies demonstrate that grass swale efficiency is influenced by multiple design factors, including vegetation type, substrate composition, hydraulic retention time, and slope gradient. Experimental and simulation-based research has contributed to a deeper understanding of swale performance under different hydrological conditions, with computational models such as SWMM and TRAVA playing a pivotal role in assessing runoff regulation capabilities [99]. Through this literature analysis of the hydrological performance of vegetated swales, analyses showed that there is a lack of data in the global literature regarding cost-effective design strategies, long-term maintenance protocols, and systemic integration with other green infrastructure systems [100].
By employing bibliometric methods, this study systematically consolidated global research advancements on the hydrological performance of vegetated swales, elucidating their knowledge evolution trajectories and persisting research gaps in the domains of hydrological mechanisms analysis, design optimization strategies, and functional enhancement. Future research should focus on developing innovative, low-cost swale designs that enhance stormwater treatment efficiency while ensuring economic viability [101,102]. Additionally, further investigations into optimal vegetation selection, seasonal performance variations, and synergies with other sustainable urban drainage systems are essential [103]. Addressing these research gaps will strengthen the scientific foundation for grass swale implementation, ensuring their sustainable integration into urban flood management frameworks and contributing to resilient and climate-adaptive cities.

Author Contributions

Conceptualization, X.W. and R.Z.; methodology, X.W., R.Z. and M.W.; software, R.Z. and Q.H.; validation, R.Z., Q.H. and C.S.; formal analysis, X.W.; investigation, R.Z. and Q.H.; resources, R.Z. and C.S.; data curation, R.Z. and G.C.; writing—original draft preparation, X.W., R.Z. and R.M.A.I.; writing—review and editing, R.M.A.I., M.W. and G.C.; visualization, R.Z.; supervision, X.W.; project administration, X.W., M.W. and G.C.; funding acquisition, X.W., M.W. and G.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Philosophical and Science Foundation of Guangdong Province [grant number GD23XYS033]; the Guangdong Basic and Applied Basic Research Foundation, China [grant number 2023A1515030158]; the Guangzhou City School (Institute) Enterprise Joint Funding Project, China [grant number 2024A03J0317]; and the 2023 Hunan Provincial Department of Education Outstanding Youth Scientific Research Project [grant number 23B1038].

Data Availability Statement

This study did not report any publicly archived datasets.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Flow chart of the study.
Figure 1. Flow chart of the study.
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Figure 2. Analysis of the research on the role of grass swales in urban stormwater management derived from the WOS database.
Figure 2. Analysis of the research on the role of grass swales in urban stormwater management derived from the WOS database.
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Figure 3. National cooperation network map in grass swale research.
Figure 3. National cooperation network map in grass swale research.
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Figure 4. National research output on the water purification performance of grass swales (2000–2023).
Figure 4. National research output on the water purification performance of grass swales (2000–2023).
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Figure 5. Co-citation network of the literature focusing on the water purification service of grass swales.
Figure 5. Co-citation network of the literature focusing on the water purification service of grass swales.
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Figure 6. Temporal distribution of the keywords related to the purification function of grass swales (2000–2023).
Figure 6. Temporal distribution of the keywords related to the purification function of grass swales (2000–2023).
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Figure 7. Burst detection results for keywords related to the water purification function of grass swales using CiteSpace.
Figure 7. Burst detection results for keywords related to the water purification function of grass swales using CiteSpace.
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Figure 8. National research output on the runoff regulation performance of grass swales (2000–2023).
Figure 8. National research output on the runoff regulation performance of grass swales (2000–2023).
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Figure 9. Co-citation network of the literature focusing on the runoff regulation service of grass swales.
Figure 9. Co-citation network of the literature focusing on the runoff regulation service of grass swales.
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Figure 10. Temporal distribution of the keywords related to the runoff regulation function of grass swales (2000–2023).
Figure 10. Temporal distribution of the keywords related to the runoff regulation function of grass swales (2000–2023).
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Figure 11. Burst detection results for keywords related to the runoff regulation function of grass swales using CiteSpace.
Figure 11. Burst detection results for keywords related to the runoff regulation function of grass swales using CiteSpace.
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Table 1. Top ten authors in grass swale research.
Table 1. Top ten authors in grass swale research.
AuthorCountryResearch CenterPublication NumberThe Year the Paper Was First Published
Viklander, Maria SwedenSwedish Meteorological and Hydrological Institute72018
Hunt, William FrederickUSANorth Carolina State University52012
Gulbaz, SezarIranIstanbul University52014
Kazezyilmaz-Alhan, Cevza MelekIranCerrahpasa Istanbul University52014
Marsalek, JiriSwedenLulea University of Technology52018
Deletic, AnaAustraliaCooperative Research Centre for Water Sensitive Cities42001
Leonhardt, GuntherSwedenLulea University of Technology42018
Field, RichardUSAUniversity of Nottingham32009
Gavric, SnezanaIranLulea University of Technology32019
Bell, ColinUSAColorado School of Mines32020
Table 2. Top ten countries contributing to research on grass swales.
Table 2. Top ten countries contributing to research on grass swales.
CountryPublication NumberThe Year the Paper Was First Published
USA702001
China562005
Australia172003
South Korea142008
Malaysia112011
Sweden102002
England92003
Iran82019
Canada72006
Netherlands62003
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MDPI and ACS Style

Wang, X.; Zhang, R.; Hu, Q.; Sun, C.; Ikram, R.M.A.; Wang, M.; Cheng, G. Assessment of the Hydrological Performance of Grass Swales for Urban Stormwater Management: A Bibliometric Review from 2000 to 2023. Water 2025, 17, 1425. https://doi.org/10.3390/w17101425

AMA Style

Wang X, Zhang R, Hu Q, Sun C, Ikram RMA, Wang M, Cheng G. Assessment of the Hydrological Performance of Grass Swales for Urban Stormwater Management: A Bibliometric Review from 2000 to 2023. Water. 2025; 17(10):1425. https://doi.org/10.3390/w17101425

Chicago/Turabian Style

Wang, Xuefei, Run Zhang, Qi Hu, Chuanhao Sun, Rana Muhammad Adnan Ikram, Mo Wang, and Guo Cheng. 2025. "Assessment of the Hydrological Performance of Grass Swales for Urban Stormwater Management: A Bibliometric Review from 2000 to 2023" Water 17, no. 10: 1425. https://doi.org/10.3390/w17101425

APA Style

Wang, X., Zhang, R., Hu, Q., Sun, C., Ikram, R. M. A., Wang, M., & Cheng, G. (2025). Assessment of the Hydrological Performance of Grass Swales for Urban Stormwater Management: A Bibliometric Review from 2000 to 2023. Water, 17(10), 1425. https://doi.org/10.3390/w17101425

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