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Sponge basin could help prevent flooding

Stunning images of a flash flood in the region between Nepal and Tibet in Asia made headlines around the world. In Brazil, they brought to mind the floods that have occurred in various regions in recent years. Occurring with increasing frequency and intensity, these extreme weather events share the same root cause: global warming. According to Cecília Herzog, a Brazilian urban landscape architect with the Network of Experts in Nature Conservation (RECN), climate change requires adaptations that go beyond urban areas. “We need to consider the hydrological process as a whole and adapt watersheds,” she says. Notícias relacionadas:Desertification in Brazil threatens food and water security.Heat waves still neglected in Brazil, says researcher.Restaura Biomas to restore 600,000 ha of native vegetation in Brazil.“Water does not respect political decisions, conventions, or borders; nature’s boundaries are diferente - it has its own processes and flows across the landscape,” she notes. Based on this idea, the expert proposes adopting a model called the “sponge watershed,” an adaptation of the “sponge city” concept popularized by Chinese architect Yu Kongjian in the early 2000s. The approach focuses on managing river courses themselves rather than adapting cities to absorb, retain, and reuse rainwater through nature-based solutions. “When you start treating the watershed as a planning unit - which is the ideal unit - you have to begin at the headwaters and extend all the way to the mouth, encompassing the entire watershed - not just the river itself, but also all the surrounding areas that will, in some way, affect what happens,” she explains. For Juliana Baladelli Ribeiro, an expert in nature-based solutions and a manager at the Boticário Group Foundation, slowing runoff within the river system itself is more effective than focusing solely on the effects of rainfall in cities. “The excess rainfall that causes disruptions in cities often doesn’t fall directly there. The water accumulates throughout the watershed and flows in via the rivers,” she points out. In practice, the main interventions would be to protect the headwaters in the upper parts of watersheds and restore forests along riverbanks to maintain the natural connectivity of vegetation across the landscape. Ribeiro believes that interventions in watersheds do not preclude action in cities, where it is also necessary to ensure that the increased volumes of water accumulating during heavy rains can drain properly. She proposes “having spaces such as urban parks, rain gardens, and wet squares, which help retain this water and thus allow it to gradually return to its natural course.” According to experts, integrated watershed management based on the “sponge watershed” concept has produced successful results in several countries, but solutions must be tailored to local conditions. “We can’t just think about importing models. We need to figure out how to transform these landscapes from extremely vulnerable to more resilient by co-creating solutions with local knowledge,” Cecília Herzog argues.