By Professor Dr Atif Amin Al Hussaini
Africa-Press – Gambia. What is a Sponge City?
A “Sponge City” is an innovative urban planning and design concept that aims to enhance a city’s resilience to water-related challenges, particularly flooding and water scarcity, by mimicking natural hydrological processes. Instead of rapidly channelling stormwater away through conventional “grey infrastructure” (pipes, drains), a sponge city absorbs, stores, filters, and slowly releases rainwater, much like a natural sponge. This is achieved through a combination of “green infrastructure” (for example, permeable pavements, rain gardens, green roofs, wetlands, urban forests) and “blue infrastructure” (for example, rehabilitated natural waterways, retention ponds).
The core objectives are:
Flood mitigation: Reducing the risk and severity of urban flooding during heavy rainfall.
Water resource management: Increasing groundwater recharge, conserving water, and providing alternative water sources for non-potable uses.
Water quality improvement: Naturally filtering pollutants from stormwater runoff.
Urban greening and biodiversity: Enhancing urban ecosystems, creating green spaces, and fostering biodiversity.
Climate change Aadaptation: Building resilience to extreme weather events, including both floods and droughts, which are increasingly common due to climate change.
The case for Greater Banjul as a Sponge City: Context and challenges
Greater Banjul, encompassing Banjul, Kanifing Region, and parts of the West Coast Region, is The Gambia’s most densely populated and economically vital area. However, it faces significant urban and environmental challenges that make the sponge city concept highly relevant.
Vulnerability to flooding: The low-lying topography of Banjul and parts of the Greater Banjul Area, combined with an outdated and inadequate drainage system, makes it highly susceptible to flash floods during the rainy season. Recent years have seen devastating floods, displacing thousands and causing significant economic losses.
Climate change impacts: The Gambia is highly vulnerable to climate change. Rising sea levels pose an existential threat to Banjul, with projections indicating that a one-meter rise could submerge a significant portion of the city. Increased intensity of rainfall events, even if overall rainfall decreases, exacerbates flood risks. Saltwater intrusion into freshwater aquifers is also a growing concern.
Aging infrastructure: The existing drainage and sewage systems are largely outdated, insufficient, and poorly maintained, leading to a host of public health and environmental issues, including the discharge of untreated wastewater into the River Gambia estuary.
Urbanisation and uncontrolled development: Rapid urbanisation and often unplanned development contribute to the loss of natural permeable surfaces (for example, mangroves, wetlands), increasing runoff and exacerbating flooding.
Water scarcity concerns: While floods are a major issue, there are also concerns about freshwater availability, particularly with increased salinity due to saltwater intrusion and reduced groundwater recharge.
Implementing sponge city principles in Greater Banjul is not merely an urban planning choice but a critical strategy for the long-term sustainability, resilience, and prosperity of The Gambia as an emerging nation.
Roadmap for The Gambia Government to convert Greater Banjul into a Sponge City
Phase 1: Planning and capacity building (1-2 years) Policy and regulatory framework
National Sponge City policy: Develop a national policy framework to guide the initiative, integrating it with existing climate change adaptation, urban development, and water management policies.
Legislation and by-laws: Enact or amend building codes, zoning regulations, and environmental laws to mandate sponge city elements in new developments and incentivise retrofitting.
Institutional coordination: Establish a dedicated inter-ministerial task force (for example, Ministries of Urban Development, Environment, Water Resources, Works, Local Government) and a technical working group to oversee and coordinate the initiative.
Assessment and masterplan development
Detailed hydrological study: Conduct a comprehensive study of Greater Banjul’s hydrology, including rainfall patterns, soil permeability, groundwater levels, and existing drainage infrastructure.
Vulnerability mapping: Identify areas most prone to flooding and vulnerable to sea-level rise.
Sponge City master plan: Develop a strategic master plan for Greater Banjul, outlining specific interventions, target areas, timelines, and responsible agencies. This plan should integrate with the Greater Banjul Area Sustainable Urban Development Programme 2020-40 (GBA-SUDP).
Capacity building and awareness
Training programmes: Provide extensive training for government officials, urban planners, engineers, architects, landscape designers, and construction workers on sponge city principles, design, implementation, and maintenance.
Public awareness campaigns: Launch nationwide campaigns to educate citizens about the benefits of sponge cities, encourage household-level interventions (for example, rain barrels, small rain gardens), and foster community participation.
Knowledge exchange: Foster partnerships with international organisations and cities experienced in sponge city implementation (for example, Chinese cities, Rotterdam, Singapore).
Phase 2: Pilot Projects and Scaled Implementation (3-7 Years) pilot projects
Demonstration areas: Select a few highly vulnerable or rapidly developing areas within Greater Banjul for pilot sponge city projects. These could include specific neighbourhoods, public parks, or commercial zones.
Diverse interventions: Implement a range of green and blue infrastructure solutions, such as:
Permeable pavements: Replace impermeable roads, sidewalks, and parking lots with permeable materials.
Rain gardens and bioswales: Create landscaped depressions that collect and filter stormwater.
Green roofs and walls: Install vegetation on rooftops and vertical surfaces to absorb rainwater and reduce heat.
Constructed wetlands: Develop small-scale wetlands for natural water purification and storage.
Urban parks and green spaces: Design parks to function as retention areas during heavy rainfall.
Rainwater harvesting: Promote and incentivise rainwater harvesting systems for homes and public buildings.
Rehabilitation of natural waterways: Restore and protect natural streams and mangrove areas.
Financing strategy
Budget allocation: Dedicate significant national budget allocations for sponge city projects.
International funding: Actively seek grants and loans from multilateral development banks (for example, African Development Bank, World Bank), climate funds (for example, Green Climate Fund), and bilateral donors.
Public-private partnerships (PPPs): Explore PPP models for financing and implementing large-scale projects.
Local revenue generation: Consider mechanisms like stormwater fees or environmental levies to support long-term maintenance.
Monitoring and Evaluation: Establish robust monitoring and evaluation frameworks to track the effectiveness of interventions in reducing flooding, improving water quality, and increasing groundwater levels.
Regularly assess the socio-economic and environmental impacts.
Phase 3: Scaling up and long-term sustainability (beyond 7 years)
Full-scale implementation: Gradually expand sponge city interventions across the entire Greater Banjul area, integrating the principles into all new urban development projects and retrofitting existing infrastructure.
Maintenance and operation: Develop clear guidelines and allocate dedicated resources for the long-term maintenance and operation of sponge city infrastructure. This often involves community engagement and local ownership.
Innovation and research: Encourage local research and innovation in sustainable water management solutions tailored to The Gambia’s specific context.
Replication: Explore the possibility of replicating successful sponge city models in other vulnerable urban and peri-urban areas across The Gambia.
Impact for The Gambia and lives of its people
Converting Greater Banjul into a sponge city would have profound positive impacts:
Reduced waterborne diseases: Less stagnant water reduces breeding grounds for mosquitoes (malaria, dengue) and minimises contamination of water sources from overflowing sewage during floods, leading to a decrease in waterborne diseases like cholera and typhoid.
Better sanitation: Improved drainage and reduced flooding will alleviate pressure on inadequate sanitation systems, leading to healthier living conditions.
Enhanced safety and security
Reduced flood risk: Most direct impact is significantly lower risk of flash floods, protecting homes, businesses, and lives. This reduces displacement and trauma associated with severe flooding.
Safer commutes: Roads will be less prone to inundation, ensuring smoother movement of people and goods.
Improved quality of life
Greener and cooler cities: Increased green spaces, trees, and permeable surfaces will reduce the urban heat island effect, making the city cooler and more comfortable, especially during hot seasons.
Aesthetic appeal: More parks, green spaces, and natural waterways will enhance the beauty and livability of the urban environment.
Recreational opportunities: Well-designed green and blue spaces can provide valuable recreational areas for residents.
Food security (indirect): By reducing flooding in low-lying areas, especially those used for urban agriculture, it can indirectly support local food production.
Source: The Standard Newspaper | Gambia
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