Bioswales are a method of using soil and vegetation to slow the arrival of water into storm drains, while also ensuring the roads don’t flood. They convey stormwater at a slow, controlled rate, and the flood-tolerant vegetation and soil act as a filter, cleaning runoff and allowing infiltration.
Already in use in Portland, USA, bioswales are designed to handle larger quantities of water that flow from impervious surfaces like parking lots and city streets. In locations with low infiltration rates, underdrains can be used to collect excess water and discharge the treated runoff to another green infrastructure practice or storm sewer system.
The image below, is an example image of a Bioswales that can be applied to a constantly flood road network in Lagos.
Permeable pavements include both pavements and pavers with void space for greenery. Runoff can flow through and be temporarily stored in an underground stone base prior to infiltrating into the ground or discharging from an underdrain. Permeable pavers use blocks of brick, stone, or concrete in a grid; permeable sand or gravel in spaces between the blocks; and a gravel or aggregate sublayer.
These permeable pavements reduce annual runoff volumes by approximately 60 per cent, reduce peak flows, and improve water quality by removing oil and grease, metals, and suspended solids have already been installed in Denmark.
Singapore uses detention basins to deal with heavy rainfall. Grassed depressions or basins are dug which then fill with water during heavy rainfall. They play an important role in regulating water flows and maintaining water quality by retaining sediments and reducing nutrients and metals because of the settling of particulate pollutants and their uptake by vegetation. Detention basins are usually dry except in periods of heavy rainfall, and this makes it possible to be used for other functions (e.g. recreation), hence have the potential to provide multiple amenity benefits.
By learning from successful implementations of green infrastructure in other cities such as Portland’s Grey to Green Initiative, Copenhagen’s Cloudburst Management Plan, and Singapore’s ABC Waters Program, Lagos State can also develop a robust and adaptive flood management strategy. Investing in green infrastructure will not only reduce the frequency and impact of floods but will also contribute to the overall improvement of urban life through enhanced biodiversity, recreational spaces, and cleaner air and water.
As Lagos continues to grow and evolve, it is essential for policymakers, urban planners, and the community to work collaboratively in implementing these green solutions. Embracing a holistic approach that combines both traditional and green infrastructure will be key to building a resilient, sustainable, and thriving city capable of withstanding the challenges posed by pluvial flooding and climate change.
Photo credit: Wikicommons used with permission CC BY-SA 4.0