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| Source: bilanol/elements.envato.com |
Discover how sustainable site design and innovative stormwater strategies can transform urban landscapes. From green roofs and bioswales to inspiring case studies, explore how these eco-friendly initiatives not only mitigate the impacts of stormwater runoff but also enhance biodiversity, improve water quality, and create resilient, vibrant urban environments.
Relevant article: Cooler Cities, Greener Spaces: Strategies for Sustainable Site Selection and Design
The Problems with Grey Infrastructure
In today's world, urban development is inevitable. As cities continue to grow and expand, the challenges of managing stormwater runoff become increasingly important. Water that falls as rain is known as stormwater. In traditional urban areas with extensive impervious surfaces such as roads, parking lots, and buildings, stormwater runoff is unable to infiltrate into the ground, leading to increased surface runoff.
The increased prevalence of impervious surfaces limits natural infiltration, leading to higher volumes of runoff and increasing the risks of flooding and erosion. Moreover, this runoff carries pollutants from the urban environment, such as oils, chemicals, and sediments, before being discharged into water bodies.
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| Extensive impervious surfaces. Source: halfpoint/elements.envato.com |
The conventional response to stormwater management involves the utilisation of grey infrastructure, predominantly composed of concrete and steel. This infrastructure encompasses storm drains, underground pipes, and detention ponds designed to collect and channel stormwater to nearby water bodies.
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| Gray infrastructure. Source: APchannel/elements.envato.com |
Despite its widespread use, traditional stormwater management practices based on grey infrastructure exhibit adverse environmental consequences. They disrupt natural hydrological processes, contribute to urban heat island effects, increase peak flows, degrade water quality in receiving streams and rivers, and reduce groundwater recharge.
Green Infrastructure: A Nature-Based Approach to Stormwater Management
A more sustainable approach to stormwater management involves the implementation of green infrastructure practices. Green infrastructure, also known as nature-based or sustainable urban drainage systems, leverages natural features and processes to manage stormwater runoff in a more eco-friendly and effective manner. This approach utilises infiltration and vegetative solutions that mimic the natural conditions of undeveloped land by allowing water to access the soil.
Strategies for treating and infiltrating stormwater all use permeable surfaces and include rain garden depressions and vegetated swales that replace concrete channels or pipes, porous paving that lets water infiltrate the soil instead of running off, and green roofs that soak up water instead of shunting it directly into storm drains. Blue-Green Infrastructure, Low-Impact Development, Nature-Based Solutions, and the Sponge City Program are all examples of sustainable stormwater management practices that aim to minimise the negative impacts of urban development on stormwater runoff.
Benefits of Sustainable Stormwater Management
Incorporating green infrastructure in site design achieves multiple goals:
1. They help to capture and slow down the flow of stormwater, allowing for better absorption into the soil, reducing the volume and velocity of runoff and preventing it from overwhelming drainage systems. This not only helps to prevent erosion of stream banks and channels and reduces the risk of flooding in urban areas but also allows for the replenishment of groundwater.
2. They play a pivotal role in enhancing ecosystem services. They act as natural filters, helping to remove or reduce the amount of pollutants in stormwater, thus improving water quality.
3. They can lower costs by replacing much of the expensive stormwater grey infrastructure that would otherwise have been constructed.
4. They act as a haven for diverse flora and fauna, helping to preserve biodiversity in urban environments. By maintaining and protecting these ecological systems, cities can ensure the survival of various species and contribute to the health of the overall ecosystem.
5. These natural ecosystems contribute to air quality improvement and carbon sequestration and aid in temperature regulation in urban areas through shading and evapotranspiration.
6. Many places designed to infiltrate and treat stormwater are aesthetically pleasing green spaces for communities to enjoy, thus enhancing the overall quality of urban environments and improving the well-being of residents.
Principles of Sustainable Stormwater Management
All sustainable stormwater management practices are based on the same fundamental principles [1]:
1. Think small: sustainable stormwater management focuses on the infiltration of small, frequent rain events to restore a watershed's function and groundwater replenishment. This approach prioritises water from these smaller storms to infiltrate the soil, as they contribute significantly more to groundwater recharge compared to larger, infrequent storms.
2. Start at the source: sustainable stormwater management retains the water where it falls instead of transporting it. Treating and infiltrating a small amount of water at a time, when repeated in multiple locations throughout an urban area and when repeated for every small storm and the beginning of every large storm, will restore water quality, reduce flooding, and replenish groundwater.
3. Minimise impervious surfaces: water that runs off impervious surfaces, especially paving, picks up pollutants, including oil, heavy metals, and chemicals, and carries them into storm drains and water bodies. Without access to plants and soils that could remove suspended soils and break down petroleum, sequester metals, and pesticides, the pollutants become concentrated. This contaminated water then moves into pipes and eventually reaches streams, rivers, and other water bodies. Sustainable stormwater management, in addition to restoring stream baseflows and replenishing groundwater, is essential for removing pollutants from water.
Sustainable Stormwater Management Strategies
Urban stormwater runoff must be managed using the best management strategies to reduce or prevent pollution from entering our water bodies. The best-known stormwater management strategies include rain gardens, vegetated swales, permeable paving, green roofs, and constructed wetlands.
Rain Gardens
Rain gardens are planted depressions in the landscape, small basins where stormwater runoff is allowed to collect temporarily as it infiltrates into the soil. Water collects in these depressions after a storm and is gone in 72 hours or less. These depressions are typically filled with native plants that can tolerate both wet and dry conditions, helping to retain and filter stormwater pollutants from residential yards and driveways [2].
See rain garden in Butterworth, Penang, Malaysia.
Swales
Vegetated swales, on the other hand, are linear, shallow, landscaped channels that collect and convey stormwater runoff. Swales have greater water-holding capacity than rain gardens and typically consist of grasses, native plants, or engineered materials. They are useful for catching and treating runoff from parking lots and for disconnecting impervious sections of parking lots from each other. Swales reduce stormwater velocity, infiltrate and recharge groundwater, and cleanse stormwater by removing, breaking down, and storing pollutants [3].
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| Eco-friendly open parking areas - built with vegetated swales and permeable pavements. Source: CreativeNature_nl/elements.envato.com |
A bioswale is a stormwater treatment swale planted with native or locally adapted plants. This is because the dense vegetation in a swale does a lot of work of slowing, retaining, and treating stormwater runoff--plants in a swale work as sponges, storing a lot of water. The roots help to break up the soil and create voids for water to move into, promoting infiltration and reducing runoff. Both the plants and roots remove and hold sediments and take up heavy metals, nutrients, and other pollutants, providing a natural filtration system for stormwater [4].
Bacteria and other microorganisms in the soil also play a crucial role in breaking down petroleum-based products and other organic pollutants such as pesticides and fertilizers. Since they do this work slowly, the water needs to stay in the soil beneath a swale long enough to allow for these processes to occur.
Permeable (or Porous or Pervious) Paving
Impermeable surfaces (also called impervious surfaces) are building roofs, sidewalks, parking lots, and driveways made from materials that do not allow rainwater to pass through, such as concrete or asphalt. To mitigate the impacts of stormwater runoff from these impervious surfaces, permeable (also called porous or pervious) paving techniques have gained popularity in sustainable stormwater management.
These techniques involve using permeable pavements, such as pervious concrete, porous asphalt, grasscrete pavers and permeable interlocking pavers, which are designed to allow water to permeate through the surface and into a stone base or underlying soil, where it can be naturally filtered and infiltrated.
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| Grasscrete pavers and permeable interlocking pavers. Source: leungchopan/elements.envato.com |
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| Permeable pavements. Source: uladzimirz/elements.envato.com |
When a system allows stormwater to infiltrate through the soil slowly, it removes pollutants. Soil collects pollutant particles from water, just like an air filter collects dust particles from the air. In order to use the infiltration treatment types, it is necessary to have site soil with moderate permeability rates. Soils with very high infiltration rates will release the stormwater directly into groundwater without having time to filter pollutants, and soil with very low infiltration rates will not filter the water at all.
Bioswales are frequently incorporated into parking areas, especially where surfaces are impermeable. Connected impervious areas can lead to the rapid formation of concentrated flows of polluted runoff, which is disconnected from groundwater. These concentrated flows can cause erosion, carry pollutants into water bodies, and overwhelm traditional stormwater grey infrastructure.
One objective of stormwater management is to fragment these impermeable areas into separated, unconnected patches. Swales, rain gardens, and other infiltration zones are utilised to isolate these areas and redirect their flow towards plants and soil. The ground beneath the impermeable patches stays connected with the soil and underground; however, the impervious surfaces above are isolated. By directing runoff from impervious surfaces into infiltration areas, it decreases both the volume and speed of stormwater runoff, thus averting erosion and flooding [5].
Green Roofs
A green roof (also called living roof) is a type of green infrastructure that involves the installation of vegetation on the roof of a building. It is like a rain garden but situated on top of a building. With their vegetation and soil layers, green roofs act as sponge-like surfaces that capture and hold rainwater, allowing it to slowly infiltrate into the ground rather than rapidly draining into stormwater systems. This process allows pollutants to be filtered out and reduces the volume of stormwater runoff, minimising the strain on stormwater management systems [6].
The benefits of green roofs extend beyond stormwater management. They store carbon and contribute to mitigating the urban heat island effect. Furthermore, green roofs can contribute to energy savings by insulating buildings and reducing the need for heating and cooling [7,8].
Moreover, green roofs can improve biodiversity in urban environments by providing habitat for animals and plants [9]. They enhance the aesthetic appeal of buildings, providing visual relief from traditional rooftops and creating opportunities for recreational spaces. When green roofs are used for urban farming, they can enhance food security by reducing reliance on conventional agriculture and promoting localised production and distribution. Overall, green roofs are a sustainable and effective solution for stormwater management in urban areas.
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| Green roofs of residential buildings in Duesseldorf, Germany. Source: wirestock/elements.envato.com |
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| Extensive living roof at the Skelton Lake Service Station, Leeds, UK. Source: jacksonnick/elements.envato.com |
Case Studies
Successful implementation of sustainable stormwater management practices has been demonstrated through various case studies. Here are several specific examples of successful sustainable stormwater management projects:
1. The Green City, Clean Water programme in Philadelphia, USA, has implemented green infrastructure projects such as rain gardens, permeable pavement, and green roofs to manage stormwater. The programme has resulted in significant reduction in stormwater runoff, improved water quality, and enhanced community green spaces [10].
2. The Sponge City initiative in China, has utilised sustainable stormwater management practices, including the implementation of green roofs, to address urban flooding and water scarcity issues in highly urbanised areas. These practices have shown promising results in managing stormwater runoff and reducing the impact of urban development on water resources [11].
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| Roof garden in Shenzhen City, China. Source: lzf/elements.envato.com |
3. A bioretention project at the Agripolis Campus of the University of Padova, Italy, effectively reduced runoff and improved water quality. The project evaluated the efficiency of two bioretention solutions, including a rain garden system and a bioretention pond with impervious walls, both aimed at intercepting and retaining stormwater runoff, reducing peak discharge, and decreasing pollutants in overflow water [12].
4. Singapore's extensive network of green spaces and parks, including rooftop gardens and vertical greenery, has enhanced biodiversity and provided essential ecosystem services in urban areas. The city's commitment to incorporating nature-based solutions has improved air and water quality, creating a more resilient and sustainable urban environment [13]. Mapletree Business City II in Singapore is a notable example of sustainable stormwater management, with its innovative design featuring bioswale and green roofs that effectively manage and treat stormwater runoff, reducing the impact on local water bodies.
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5. Examples of eco-friendly developments that incorporate sustainable stormwater management practices in Malaysia are Setia Eco Glade and Setia EcoHill. They include features such as rain gardens, bioswales, and detention ponds to capture and treat stormwater runoff while promoting groundwater recharge and improving water quality. They also utilise green roofs and permeable pavements to manage stormwater runoff effectively. By incorporating these nature-based solutions into urban and site designs, the townships demonstrate the potential for sustainable development that addresses the challenges of urbanisation while prioritising environmental sustainability and the well-being of their residents.
Conclusion
In conclusion, the shift toward sustainable stormwater management is imperative in our evolving urban landscape. As traditional methods prove environmentally detrimental, the embrace of green infrastructure emerges as a transformative solution. Examining global examples, from Singapore to Philadelphia, underscores the effectiveness of eco-friendly initiatives in mitigating stormwater impacts and enhancing urban resilience.
The principles of sustainable stormwater management, advocating for small-scale thinking, source-focused approaches, and reduced impervious surfaces, lay a robust foundation. Strategies like rain gardens, vegetated swales, and green roofs not only capture stormwater but also deliver multifaceted benefits--improved water quality, cost savings, biodiversity preservation, and aesthetic enhancements.
The showcased case studies and innovative projects in Malaysia and elsewhere exemplify the tangible success of sustainable stormwater practices. By seamlessly integrating nature-based solutions into urban design, these developments illuminate a path where urbanisation aligns with environmental preservation.
In essence, sustainable stormwater management signifies more than a technical necessity; it represents a holistic paradigm where urban development harmonises with ecological well-being. Embracing these principles and strategies propels cities toward resilience, sustainability, and the flourishing coexistence of residents and the environment.
References
[1] Burns, M. J., Fletcher, T. D., Walsh, C. J., Ladson, A. R. and Hatt, B. E. (2012). Hydrologic shortcomings of conventional urban stormwater management and opportunities for reform. Landscape and Urban Planning, 105(3), 230-240.
[2] Morash, J., Wright, A. N., LeBleu, C., Meder, A., Kessler, R., Brantley, E. & Howe, J. A. (2019). Increasing sustainability of residential areas using rain gardens to improve pollutant capture, biodiversity and ecosystem resilience. Sustainability, 11(12), 3269.
[3] Lucke, T., Mohamed, M. A. K., & Tindale, N. (2014). Pollutant removal and hydraulic reduction performance of field grassed swales during runoff simulation experiments. Water, 6(7), 1887-1904.
[4] Wells, J. & Wilson, G. (2022). Sediment deposition characteristics in shallow saturation excess overland flow for urban stormwater applications. Hydrological Processes, 36(8).
[5] Vogel, J. R., Moore, T. L., Coffman, R., Rodie, S. N., Hutchinson, S. L., McDonough, K. R., McLemore, A. J, & McMaine, J. (2015). Critical review of technical questions facing low impact development and green infrastructure: A perspective from the Great Plains. Water Environment Research, 87(9), 849-862.
[6] Zhang, Q., Miao, L., Wang, X., Liu, D., Zhu, L., Zhou, B., Sun, J., & Liu, J. (2015). The capacity of greening roof to reduce stormwater runoff and pollution. Landscape and Urban Planning, 144, 142-150.
[7] Rahman, A. A., Zaid, S. M., & Shuhaimi, N. D. A. M. (2022). Effects of green roof in reducing surface temperature and addressing urban heat island in tropical climate of Malaysia. Journal of Design and the Built Environment, 22(2), 1-20.
[8] Stamenkovic, G. M., Miletic, J. M., Kosanovic, M. S., Vuckovic, D., & Glisovic, M. S. (2018). Impact of a building shape factor on space cooling energy performance in the green roof concept implementation. Thermal Science, 22(1 Part B), 687-698.
[9] Coulibaly, S., Aubry, C., Provent, F., Rousset-Rouviere, S. & Joimel, S. (2023). The role of green roofs as urban habitats for biodiversity modulated by their design: A review. Environmental Research Letters, 18(7), 073003.
[10] Callahan, B. M. (2019). Green Stormwater Infrastructure for CSO Control. World Environmental and Water Resources Congress 2019.
[11] Zhang, Y., Zhao, W., Chen, X., Jun, C., Hao, J. L., Tang, X., & Zhai, J. (2020). Assessment on the effectiveness of urban stormwater management. Water, 13(1), 4.
[12] Zanin, G., Bortolini, L., & Borin, M. (2018). Assessing stormwater nutrient and heavy metal plant uptake in an experimental bioretention pond. Land, 7(4), 150.
[13] Cui, M., Ferreira, F., Fung, T. K., & Matos, J. (2021). Tale of two cities: How nature-based solutions help create adaptive and resilient urban water management practices in Singapore and Lisbon. Sustainability, 13(18), 10427.
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