How does root oriented preferential flow impact rain garden hydrology?

Amidst rapid urbanization and escalating environmental degradation in China’s urban areas due to climate change, traditional drainage systems struggle to cope with rainfall, resulting in frequent flood disasters. In response, rain gardens have emerged as ecologically practical stormwater management solutions that integrate urban flood control with landscape design. Leveraging the dual benefits of rainwater purification and aesthetic enhancement provided by vegetation, herbaceous plant-based rain gardens have assumed a pivotal role in green infrastructure. However, dedicated research on the application of herbaceous plants in rain garden design is limited, especially within China’s water-stressed context. This study employs a literature review and case analysis to explore this critical issue. Initially, it delineates the concept of the sponge city introduced by the Chinese government. Subsequently, it reviews concepts and methods of plant biodiversity design in urban settings and rain gardens and elucidates the structure and function of rain gardens. Four Chinese rain gardens in different urban environments (old industrial areas, university campuses, urban villages, and urban highway green belts) were selected to examine the selection and arrangement of herbaceous plants while identifying deficiencies in their designs. Finally, feasibility suggestions are provided for the design of herbaceous plant diversity in Chinese rain gardens. This study’s findings can provide a reference for the planting design of herbaceous plants in rain gardens for other countries and regions with similar climates and environmental conditions.

A rain garden was constructed in Shoelace Park in Bronx, New York with the goal of capturing stormwater runoff generated on part of 228th Street. As a pilot study implemented to test the overall strategy of utilizing urban park space to manage street runoff, the rain garden was monitored over a ten month period from October 2014 to July 2015. Field observations and analysis of the stormwater runoff entering the site through an inlet on 228th Street indicate that, due to the contributions from many adjacent tributary areas, the rain garden receives more water than anticipated. Results of the monitoring campaign show that the stormwater inlet on 228th Street captures runoff from an effective catchment that is about 1.6 times the designed tributary area. The rain garden retained an average of 77% of all inflows for all storms with water typically leaving the system in storms over 1 cm. It retained 96% and 45% of all inflow for all storms less than 1 cm and greater than 1 cm in total precipitation, respectively. The rain garden managed all off-site runoff from an area of 228th Street that was about 9 times its size during a 2.5 centimeter storm while receiving additional runoff from other adjacent areas. New York City is 72% impervious and 19.5% parkland. With as little as 5% of all New York City urban park space retrofit with green infrastructure performing similarly to the Shoelace Park rain garden, runoff from 35% of New York's impervious surfaces can be treated. This limited impact to the park ameliorates concerns of infringing on the park's current recreational purpose. Other cities in the United States with high impervious coverage and available park space are urged to consider this stormwater management opportunity.

Green infrastructure (GI) refers to trees, rain gardens, rain barrels, and other features that address stormwater management, climate change and other challenges facing many cities. GI is often not equitably distributed across urban landscapes, making its benefits unevenly experienced. Cities have multiple initiatives focused on different types of GI in residential areas, including underserved neighborhoods, although there is potential for GI programs to serve more privileged neighborhoods. The goal of this study was to examine GI program participants and non-participants to better understand who participates in different types of residential GI programs and why. We surveyed residents who had previously participated in Philadelphia’s GI programs as well as those who had not, comparing socio-demographics, knowledge-levels, environmental concerns, outdoor space preferences, motivations and barriers. We found that the GI program participants are on average younger, wealthier, more highly educated, and more likely to be White than our sample of residents who have not participated. Participants in tree programs have different socio-demographics and motivations as compared to those who installed green stormwater infrastructure. Future research should examine strategies to reach neighborhoods with different socioeconomic conditions and built environment characteristics, such as offering features appropriate for small properties with limited plantable space.

Stormwater pollution from residual chlorine after outdoor disinfection with sodium hypochlorite is an increasing environmental challenge due to its potential negative impact on aquatic ecosystems. Even at low concentrations, residual chlorine can disrupt the stability of water ecosystems. In this regard, stormwater treatment requires innovative and green solutions such as green infrastructure (rain gardens) using the plant phytoremediation technique to reduce the amount of residual chlorine. This study explores the interactions between residual chlorine retained by plants in a rain garden and different microelements. Selected plants were analyzed via spectroscopy, and possible interactions with elements such as chlorine (Cl), phosphorus (P), zinc (Zn), iron (Fe), calcium (Ca), potassium (K), nickel (Ni), silicon (Si), manganese (Mn), magnesium (Mg), chromium (Cr), and cadmium (Cd) were determined using Python-based analysis. Chlorine presented significant positive correlations with cadmium (0.39-0.53) and potassium (0.51-0.55), while negative correlations were found between silicon and chlorine (-0.48--0.54) and chlorine and iron (-0.45--0.51). The correlations between chlorine and microelements suggest both common uptake mechanisms and mutual interactions. These results provide a better understanding of the behavior of chlorine in rain gardens and its interactions with other materials, which is especially valuable for designing green infrastructure. This research can help to develop sustainable solutions that reduce environmental pollution and strengthen urban adaptation to climate change.

<p>Surface water flooding is the most likely cause of flooding in London, still affecting at least 3% of the area and up to 680,000 properties. Urbanization and climate change are expected to increase the impacts of urban flooding in the near future. To mitigate such problem and provide resilient ecosystem services for Europe’s largest capital, Urban Green Infrastructure adaptations have been extensively used in the last two decades in conjunction with traditional grey infrastructure. Sustainability and efficiency of green infrastructure depend on the ability of plants to emulate the natural ecosystem water and carbon cycles in the city. Considering the expected rise in temperature, changes in rainfall patterns and intensification of the urban heat island effect, existing and planned green infrastructure solutions might be vulnerable to plant water stress. Since there will be much less space available to accommodate future changes in cities, it is extremely important to think about the system’s potential performance further ahead the construction. In this study we perform a detailed evaluation of representative London parks and rain gardens to mitigate flood risk under a changing climate. Specifically, we focus on the hydrological performance of urban raingardens (consisting exclusively of low stature plants) and urban parks (as a composite of low stature vegetation and urban forests) in London. The coupled water and carbon dynamics were evaluated using the ecohydrological model Tethys-Chloris (TeC) forced with the last generation climate change projections UKCP18. Based on our simulation we disentangle the composite effects of climate change, to plant physiological responses to elevated CO2 and changes in precipitation patterns and temperature.</p><p>Our results indicate that:</p><p>(a) Changes in weather severely affect plant efficiency during the 2<sup>nd</sup> half of the 21<sup>st</sup> century;</p><p>(b) Effectiveness of green infrastructure is strongly dependent on possible climate change outcomes;</p><p>(c) Within a certain range of plausible climate changes, for the 1<sup>st</sup> half of the 21<sup>st</sup> century positive effects of changes in climate can mostly counteract negative plant physiological responses to elevated CO2, but those negative effects gradually become dominant;</p><p>(d) Efficient and sustainable design of urban green infrastructure to mitigate flooding must consider an optimal adaptive choice of plants to offset the projected negative impacts of elevated CO2 and uncertain climate.</p>

The world is struggling against extreme droughts, heavy rain, and heat waves because of climate change. These abnormal climate cause urban flood, urban heat island, and water pollution and shortage and these natural disasters not only threaten citizen’s health and amenity but also negatively affect cities economically, environmentally, and socially. Thus, this paper discusses about green infrastructure as the water sensitive urban design strategy in terms of sustainable stormwater management in the era of climate change. To do this, this paper reviews concept, context, and current trends of green infrastructure as water sensitive urban design strategy and this paper examines relations between green infrastructure and sustainable stormwater management. And then this paper analyzes various case studies on green infrastructure as water sensitive urban design strategy for sustainable stromwater management, which are categorized by city-scale's case studies such as Kallang River Bishan Park and Tanner Springs Park, site and building-scale's case studies such as Mount Tabor School rain garden, Sidwell Friends School wetlands, and California Academy of Sciences green roof, and street-scale's case studies such as NE Siskiyou Green Street, SW 12th Avenue Green Street, and Taylor 28 Green Street. After analyzing these various case studies of green infrastructure as water sensitive urban design strategy, this paper draws water sensitive urban design strategies for sustainable stormwater management. The result of analysis is as follows. Firstly, water sensitive urban design strategy for sustainable stormwater management contains various green infrastructure elements such as urabn wetlands, stormwater parks, eco-streams, green roofs, rain gardens, bio-swales, buffer strips, stormwater planters, permeable pavings, and cisterns. Secondly, these various green infrastructure elements could be applied on the various types of land-use such as buildings, roofs, roads, streets, and parking lots as well as green and water space in urban areas. Thirdly, these multi-dimensional green infrastructure could evaporate, infiltrate, filtrate, and reuse stormwater ecologically through vegetation, soil, and minerals which is applied on green infrastructure. Fourth, these biological green infrastructure could be linked and connected each other to supply more environmental benefits such as urban flood prevention, water purification, and habitat supply for plants and animals than to be applied alone on the various types of land-use. Eventually, these water sensitive urban design strategies as green infrastructure could restore ecologically urban hydrological cycle which is distorted by indiscriminate urban development and could enhance urban biodiversity which is destroyed by massive urban sprawl.

Today there is a problem of flooding of urban areas with rainwater and their slow drainage to rainwater sewage and further to the distribution collectors. There are several ways to ensure the resilience of urban areas to heavy rains and downpours. One of the current methods is "green" roofs (horizontal or sloping) ith green plantings, which is capable to absorb water. A certain amount of water is absorbed by the plants, its certain amount remains in the substratum, and the rest is filtered by several layers of the structure under the plants, which throttles the movement of it to the storm-water sewage. The second method is to collect rainwater in special storage tanks, which are located on the roof or near to the building or in the soil structure in the yard. The accumulated water is used for household needs: watering lawns, washing, flushing toilets, washing floors, cleaning pavements, etc. The third method is to absorb water and drain it by natural biological terrestrial sponge facilities: permeable surfaces, sloping terrain, natural vegetation, green structures, rain gardens, etc. These correspond to the modern concept of "sponge city". The authors propose a method of rapid drainage of rainwater using special "green structures" – rain-garden bands along the roadways. The ability to capture water by rain-garden bands has been confirmed on the example of most of the regional centres of Ukraine in case of the strongest observed precipitation. Such rapid drainage becomes especially important in the transition from cities for cars to cities for bicycles. This increases the requirements to avoid slippery roads for increasing the stability of these vehicles. In addition, the proposed rain gardens with shrubs can perform safe protective functions by extinguishing the kinetic energy of bouncing cars during a road accident.

Green infrastructure (GI) is quickly gaining ground as a less costly, greener alternative to traditional methods of stormwater management. One popular form ofGIis the use of rain gardens to capture and treat stormwater. We used life cycle assessment (LCA) to compare environmental impacts of residential rain gardens constructed in the Shepherd's Creek watershed of Cincinnati,Ohioto those from a typical detain and treat system.LCAis an internationally standardized framework for analyzing the potential environmental performance of a product or service by including all stages in its life cycle, including material extraction, manufacturing, use, and disposal. Complementary to the life cycle environmental impact assessment, the life cycle costing approach was adopted to compare the equivalent annual costs of each of these systems. These analyses were supplemented by modeling alternative scenarios to capture the variability in implementing aGIstrategy. OurLCAmodels suggest rain garden costs and impacts are determined by labor requirement; the traditional alternative's impacts are determined largely by the efficiency of wastewater treatment, while costs are determined by the expense of tunnel construction. Gardens were found to be the favorable option, both financially (~42% cost reduction) and environmentally (62‐98% impact reduction). Wastewater utilities may find significant life cycle cost and environmental impact reductions in implementing a rain garden plan.

Urban areas, characterized by impervious surfaces, produce storm water runoff which during unexpected heavy rainfall exceeds the carrying capacity of the storm water drainage system causing urban flooding. Transport expressways are massive hard-scaped surfaces generating large amounts of polluted surface run-off during the rains. In the case of the Nandi Infrastructure Corridor Enterprises (NICE) Expressway at Bengaluru, India, which is also a tolled road, the demonstration is about using the surface run-off or stormwater as a resource for developing urban green infrastructure complementing the transport grey infrastructure. The functions of urban green infrastructure include air quality improvement, microclimate modification, storm water management, biodiversity, recreational opportunities and visual aesthetics. Here we show, that the surface runoff or stormwater is effectively channelled to the areas around, to mark the beginning of a well-planned and executed drainage system, maintenance-free landscape and technically a sound, urban green infrastructure in the form of site-specific models of Rain Gardens. The same models can be used in other transport expressways as they are the indicators of economic growth and connectivity although would require to be customized as per the city and its climatic conditions. This paper explores three different scenarios with a typical model of development of green infrastructure along the transport expressway tailormade for each of the situations. While in the first and the second models, the Central Rain Garden and the Edge Rain Garden have been respectively proposed, the third model explores a comparatively complex scenario in the form of an Intersection Rain Garden.

Key Points: Affordable sensors allow continuous monitoring of soil moisture and hydrological performance in rain gardens. Using sensors for predictive maintenance lowers expenses and increases the longevity of rain gardens.  Rain gardens (RG) are essential for sustainable stormwater management, but their effectiveness relies on consistent maintenance, which is both critical and costly. This study explores the use of low-cost electronic sensors to monitor biofilter conditions and enable predictive maintenance, reducing manual inspections and improving operational efficiency.The experiment involved 15 laboratory-scale columns, replicating the typical structure of rain gardens, with stratified layers: a ponding zone, fine sand filter, coarse sand with mulch transition layer and a gravel drainage layer. The columns were divided into three groups to simulate different conditions: a control group (C) representing optimal performance, a group with preferential flow paths (P) simulating surface erosion, and one with surface clogging (S) due to sediment accumulation. Each column had five sensors to monitor soil moisture and temperature: two Chameleon Soil Water Sensors, two temperature probes, and one Truebner SMT 100 sensors. Data were collected in real time and transmitted to a cloud-based system. To evaluate the columns, simulated rainfall events, reflecting varying intensities and antecedent dry periods based on Melbourne’s historical weather patterns, were applied. The SMT sensor effectively tracked volumetric water content (VWC), identifying peaks from simulated rainfall events and showing variability across different antecedent dry days (ADD). However, Chameleon sensors exhibited performance degradation over time due to soil drying, root growth, and temperature variations. Inflow, outflow, and infiltration rates were measured to assess hydrological behavior, but these data alone were insufficient to differentiate healthy from malfunctioning systems. Consequently, indices were developed to differentiate the hydraulic performance of each group. Parameters such as peak time, peak span, and delay time were identified as notable in diagnosing operational states. For instance, the clogging group exhibited delayed response times and retained less water. In contrast, preferential flow columns displayed immediate responses to rainfall. Post-experimentation, the columns were disassembled to analyze physical changes in soil stratigraphy and assess root development, providing additional insights into the impact of hydraulic malfunctions on overall system health. In conclusion, this research underscores the potential of integrating low-cost sensor technologies into the management of rain gardens. Real-time monitoring not only enhances the reliability and longevity of these systems but also reduces operational costs, contributing to the broader goal of fostering resilient and sustainable urban environments. Future research should refine sensor applications and expand testing under diverse environmental conditions.

Flooding has presented a significant risk for urban areas around the world. Road inundation is one of the severe consequences leading to traffic issues and congestion. Green infrastructure (GI) offers further potential for stormwater management as an environmentally friendly and sustainable solution. However, sewer system behaviour has been overlooked in GI implementation. This study investigates sewer performance by measuring topological connectivity and hydraulic characteristics, and critical components are identified under different design storms. Three retrofit scenarios, including enlarged pipes (grey infrastructure, Grey I), rain gardens (GI), and the combination of enlarged pipes and increased rain gardens (GI + Grey I), are proposed according to the distribution of critical components. The results show that it is feasible to locate the vulnerable parts of the sewer system and GI site allocations based on the critical components that significantly impact the performance of the entire system. While all three scenarios can mitigate inundation, GI and GI + Grey I perform better than pipe enlargement, especially for runoff reduction during long-duration rainfall. Furthermore, the sewer behaviour and retrofit effect are dynamic under different rainfall patterns, leading to diverse combined effects. The discoveries reveal that the adaptation measures should combine with sewer behaviour and local rainfall characteristics to enhance stormwater management.

The urban area of Wanzhou District in Chongqing frequently experiences flooding and sewage overflow pollution due to its steep topography, frequent and intense short-duration rainstorms, and inadequate drainage capacity. To address these issues, this study integrated sponge city concepts with low-impact development (LID) measures to establish a stormwater management framework for the Guoben Road catchment area. Hydrometeorological and drainage data were obtained from local monitoring stations. Utilizing high-resolution remote sensing imagery and a 30 m-resolution digital elevation model, 50 sub-catchments were delineated in ArcGIS. Based on regional soil information and national sponge city design guidelines, a Stormwater Management Model employing the Horton infiltration method was constructed. This model simulated runoff and sewer network performance under Chicago design storm conditions with return periods of 1, 3, 5, and 10 years. Results indicate that LID facilities (permeable pavements and rain gardens) substantially reduced runoff generation and enhanced drainage system efficiency. Across the four rainfall scenarios, the total decrease in runoff volume ranged from 69.3% to 79.3%, with runoff coefficients falling from 0.51–0.61 to 0.10–0.19. The decrease in outfall discharge ranged from 11.0% to 76.1%, with peak flow reduced by up to 70.4%, most notably during the 1-year return-period event. Mitigation effects diminished during higher-return-period storms, attributed to limited LID storage capacity and rapid soil saturation, which reduced infiltration and detention capabilities during intense rainfall events. Overall, this integrated LID scheme effectively enhanced infiltration capacity within the mountainous urban catchment, reduced peak flows, and alleviated sewer network overloading. This study provides technical support for stormwater risk management, sewage overflow pollution control, and sponge city planning in Wanzhou District, Chongqing, and other cities with similar topographic and hydrological characteristics.

Optimizing the deployment of LID facilities on a campus-scale and assessing the benefits of comprehensive control in Sponge City

Flooding in the recent times is one of the society’s most significant threats from climate change and dramatic weather events. As such, integrating sponge city construction and green infrastructure have become the new paradigm for a sustainable urban storm water management policy. Sponge city initiative can be implemented in Assam too. After more than seven decades of yearly perennial floods, we know by now that the mighty Brahmaputra cannot be tamed. Nor Assam can fight climate change alone. Sponge city strategy would help Assam to work in unison with nature and sustainably manage rainwater and floodwater which could be a huge advantage not only to the environment but also to the local population as well. This paper aims to suggest certain green infrastructures and sponge city strategies which have been implemented by China and western nations in managing floods. Adopting such strategies may not be able to remove all issues completely but it might definitely work out to reduce the disastrous effect of floods. It will also help to manage water resources efficiently in the State.

As the practice of storm-water management evolves, so has our understanding of the tools. As we move away from a myopic flood control perspective, new tools to include what we now call green infrastructure best management practices (BMPs) were developed. Green roofs, rain gardens, and porous pavements appeared, with much of the design elements based on reasonable estimates of performance, thus the term “best.” Now we as a profession are moving toward a more engineered approach, with designs based on scientific knowledge of the processes, from soil physics and chemistry to hydrology and hydraulics. Soon it may be time to retire BMPs and move forward with the term “storm-water control measures,” as recommended by the National Academies authors of Urban Stormwater in the United States (National Research Council 2008). This issue of the Journal of Irrigation and Drainage Engineering is devoted to this evolving field of storm-water sustainability, and the effort to predict performance of our storm-water control measures. The 10 papers in this special issue reflect this evolution. Papers range from evaluating the concentration of effluent scoured from catch basins to cost-estimation tools, plus the inclusion of green-infrastructure tools within the International Stormwater BMP Database. Green and stone roofs are represented as are level spreaders. Bioretention/bioinfiltration rain gardens, however, received the most attention with papers on media depth, phosphorus removal, process modeling, mounding, and fines accumulation. This collection truly demonstrates our increasing knowledge base. This effort is a result of collaboration between the Stormwater Infrastructure Committee and Urban Water Resources Research Council, together with the Journal of Irrigation and Drainage Engineering Publications Committee. Conference proceedings from recent Environmental and Water Resources Institute (EWRI) congresses and low-impact development (LID) conferences were reviewed, and a select group of authors was invited to expand and revise their work. These papers passed through the standard journal peer-review process. We hope that this set of papers is of use to the profession. We would like to thank all the contributing authors, the reviewers, and William Ritter, as editor, for their efforts in this special issue.