Urban areas across the South Asian subcontinent often face significant challenges with flooding and waterlogging, especially during the monsoon season. The heavy rains often overspill the existing drainage infrastructure, leading to streets submerged in water and transportation disruptions. These events not only cause immediate disruption but also have serious economic and environmental consequences. Given that urban streets occupy a significant portion of land in cities, reimagining them as ecosystems and integrating green infrastructure can help build more resilient and sustainable urban environments.
Historically, urban development treated stormwater as waste, focusing on quickly removing runoff after rainfall. However, this approach has resulted in a massive and extensive greywater infrastructure that struggles to cope with intense storms, often leading to the outflow of polluted water into rivers and lakes. Consequently, many cities are ill-prepared to handle the increasing intensity and frequency of monsoon rains, which are further exacerbated by climate change.
During monsoons people walking, cycling or using public transit are among the first users which face hurdles and encounter a loss access to the street. Therefore the significance of addressing this problem cannot be overstated. Sponge street design is one way which ensures streets remain usable and safe for all people during storm but also considers on the green stormwater infrastructure that as a potential to transform streets and create environmental benefits.
Understanding Sponge Streets
Complete streets are an essential concept in urban planning and design, focusing on creating streets that accommodate and prioritize all modes of transportation, from walking and bicycling to public transit. However, it’s crucial to recognize that complete streets should not only be accessible and safe during typical weather conditions but also resilient during extreme events like storms. This is where the concept of “Sponge Street” comes into play. Sponge streets refer to streets designed with integrated stormwater management solutions that enhance their sustainability, resilience, and overall usability.
Sponge Streets encompass a suite of innovative interventions designed to absorb, slow down, and infiltrate stormwater within urban environments. These interventions include bioswale channels, sidewalk planters, tree trenches, and curb bulb-outs, strategically deployed to harness the power of nature in managing rainfall. By integrating these features into the built environment, cities can reduce the burden on conventional drainage systems and enhance their resilience to climate change.
Key Interventions of Sponge Streets
1.Bioswale Channels:
Bioswale channels represent a paradigm shift in stormwater management, offering a vegetated and aesthetically pleasing alternative to traditional storm sewers. Designed to convey stormwater at low velocities, filter, and infiltrate stormwater runoff, reducing peak discharge and providing up to a 10-20% runoff reduction compared to hardened channels. Implementable along roadways, parking lots, and medians, Bioswale channels effectively integrate into urban landscapes, enhancing both functionality and aesthetics.
2. Sidewalk Planters:
Sidewalk planters, also known as rain gardens or bioretention gardens, utilize vegetation and innovative drainage designs to slow down and potentially infiltrate runoff from roads and sidewalks. With components including inflow design, pre-treatment, ponding areas, overflow mechanisms, and filter media, Sidewalk Planters effectively reduce the load on stormwater systems while enhancing the streetscape experience. Well-designed planters mitigate flooding during cloudburst events, contributing to urban resilience.
3. Tree Trenches:
Tree Trenches are an innovative system of connected tree pits designed to facilitate healthy tree growth in urban areas with limited space, such as sidewalks. They offer numerous benefits, including air purification, heat island reduction, wildlife habitat creation, wind and noise buffering, and increased property values. Additionally, they play a crucial role in stormwater management by reducing runoff through rainfall interception and evapotranspiration.
A tree trench is excavated along the sidewalk and lined with permeable geotextile materials. It is then filled with stone or gravel, and the tree is planted. A special stormwater inlet directs runoff into the trench, where it is stored in the spaces between the stones. The tree roots absorb the water, which slowly infiltrates into the ground. In case of extreme flood events, a bypass system directs runoff into the existing stormwater network.
Tree Trenches: A Network of Interconnected Tree Pits for Sustainable Urban Growth_©Sponge handbook : A landscape framework for the South Buckhingam canal region of Chennai https://static1.squarespace.com/static/60b3cc8bdd6dc9347750dc27/t/60c5206d0fe1634fe83910c5/1623531644768/Team+Sponge_Sponge+Handbook-Chennai.pdf
4. Curb Bulbouts:
Curb Bulb-outs are like rain gardens or bioretention gardens that extend onto roadways, increasing green infrastructure in urban areas. They’re similar to Sidewalk Planters but are used where sidewalks are too narrow, utilizing roadway lanes or parking spaces instead. They’re especially useful at intersections, managing stormwater and enhancing pedestrian safety and experience. Curb Bulb-outs also act as traffic calming measures, slowing vehicles in areas with heavy pedestrian traffic. By extending into lanes, they reduce crosswalk distances and improve overall safety.
Design Considerations and Implementation
Effective implementation of Sponge Streets requires careful consideration of various factors, including drainage area, soil type, and hydrological characteristics. Designing for specific soil categories and ensuring adequate infiltration potential are crucial for maximizing stormwater retention and reducing runoff. Additionally, collaboration among key stakeholders, including government agencies, urban planners, engineers, and community groups, is essential for the successful implementation and long-term maintenance of sponge street interventions.
Considering the type of street network, the amount of space available and the level of stormwater management needed the stormwater elements and techniques are implemented.
- The city of Portland, Oregon, is a leading example of how streets can be transformed to manage stormwater effectively. The city’s Green Streets program has implemented a range of green infrastructure features, such as vegetated swales and stormwater planters, in streets throughout the city. These features not only help to manage stormwater but also enhance the streetscape and promote walking and cycling.
https://landperspectives.com/2011/06/02/rivereast-center-a-sustainable-site/
- In Philadelphia, Pennsylvania, the city’s Green City, Clean Waters program has transformed streets into green corridors that manage stormwater and provide multiple benefits. By incorporating features such as rain gardens, tree trenches, and porous pavement, Philadelphia has been able to reduce stormwater runoff, improve water quality, and enhance the urban environment.
- Vancouver, Canada – Rain City Strategy: Vancouver’s Rain City Strategy is a comprehensive approach to managing stormwater using green infrastructure. The city has implemented Sponge Street interventions, including Bioswales, green roofs, and permeable pavement, to reduce runoff and improve water quality. The Rain City Strategy has transformed Vancouver’s streetscapes, making them more resilient to climate change impacts.
- In India, the revitalization of Ring Road in New Delhi and Race Course Road in Coimbatore showcases the remarkable impact of integrating bioswales as a means of stormwater management. Ring Road in New Delhi has recently undergone a transformative redevelopment, featuring bioswales along its length. These bioswales effectively mitigate stormwater and reduce instances of flooding, while also enhancing the road’s aesthetic appeal with lush greenery. This rejuvenation effort has not only contributed to environmental improvements but has also bolstered property values and enhanced the overall quality of life for residents. Similarly, Coimbatore’s Race Course Road has experienced significant transformation, emphasizing sustainable urban development principles. Adorned with greenery and strategically placed bioswales, the road incorporates rainwater harvesting techniques to preserve valuable water resources. This makeover has successfully addressed stormwater challenges and notably augmented groundwater recharge rates, underscoring the project’s multifaceted benefits for the community and the environment.
Way forward
The transformation of streets through the integration sponge street (green infrastructure) tools and measures is a significant step towards creating more sustainable and liveable cities. To replicate the success of such streets, city planners should consider:
Community Engagement: Involve the local community in the planning and design process to ensure streets reflect the needs and desires of residents.
Sustainability: Prioritize sustainable practices by incorporating green infrastructure, rain gardens, and swales into street design to manage stormwater effectively.
Maintenance: Establish robust maintenance plans to ensure the longevity of urban landscaping elements and swales, preserving their aesthetic and functional value.
Embracing Sponge Streets represents a holistic approach to urban planning and design, integrating social, economic, and environmental goals. By transforming streets into multifunctional ecosystems capable of managing stormwater, cities can enhance their resilience to climate change, improve public health and well-being, and create vibrant, sustainable communities for generations to come.
As cities urbanize and face the challenges of rapid development, adopting Sponge Streets offers a path toward more equitable, inclusive, and resilient cities that thrive in adversity. These streets not only reduce flooding risks but also contribute to cleaner waterways, enhanced urban aesthetics, and a healthier environment.
However, achieving this requires a shift in mindset from viewing stormwater as waste to recognizing it as a valuable resource that can be managed sustainably. As cities evolve, it’s crucial to prioritize these design elements to minimize flooding, recharge groundwater, and transform streets into vibrant, resilient, and green urban hubs, ensuring a prosperous and harmonious future for urban communities.
Reference:
Cook, E. A. (2007). Green site design: Strategies for storm water management. Journal of Green Building, 2(4), 46-56.
National Association of City Transportation Officials. (2017). Urban Street Stormwater Guide. Island Press.
Team Sponge. (2021). Sponge Handbook: Transforming Chennai into a Water-Sensitive City. Retrieved from https://static1.squarespace.com/static/60b3cc8bdd6dc9347750dc27/t/60c5206d0fe1634fe83910c5/1623531644768/Team+Sponge_Sponge+Handbook-Chennai.pdf
