The South Zone of Rio de Janeiro, nestled between the Atlantic coastline and the slopes of the Maciço da Tijuca, is home to small-scale river basins that are nonetheless fast-flowing and of great ecological importance. These are watercourses that run down steep hillsides, through narrow valleys, forming waterfalls, pools, and rapids, before reaching the narrow coastal plains where densely urbanized neighborhoods such as Cosme Velho, Laranjeiras, Flamengo, Botafogo, Copacabana, Ipanema, Leblon, Jardim Botânico, Gávea, and São Conrado are now located.
On the steepest slopes of the Maciço da Tijuca, drainage patterns are highly controlled by ancient fractures and faults in the rocks. Heavily fractured, these rock formations channel water into rivers with angular patterns, often forming abrupt drops in the higher stretches, where the formations favor the occurrence of natural steps.
Image description: This is a photograph of a waterfall located in a forested area. On the left side, we see darkened rocks covered with green moss. Moving toward the center, we see the main waterfall, with water flowing in three distinct strands. The water forms a small pool at the base of the waterfall. On the right, more rocks and dense vegetation are visible. In the foreground, stones of different sizes and shapes are arranged, some covered with green moss.Cachoeira do Chuveiro or do Box waterfall, formed within the rock fractures, in Horto, Tijuca National Park (PNT-ICMBio)
Among the best-known springs is that of the Carioca river, which rises on the slopes of Tijuca National Park, between Serra da Carioca and Corcovado Hill. In its upper course, the Carioca forms beautiful stretches with lush forest and riparian vegetation, rapids and waterfalls before flowing on, channeled between the neighborhoods of Cosme Velho, with its stretch honored by plaques at Largo do Boticário, and Laranjeiras, emptying into the Flamengo inlet. Despite intense urbanization, this river still holds symbolic importance, being one of the city's oldest water landmarks, having supplied the famous Arcos da Lapa aqueduct all the way to Largo da Carioca, with its waters distributed through the public fountains of the historic beginnings of urban settlement.
In the neighborhood of Botafogo, two small rivers run through the sandy lowland beneath the now densely occupied district. They are the Bengó and Banana Podre rivers, which flow through underground galleries beneath the neighborhood's main streets, with no points where they can be seen.
In the neighborhood of Copacabana, the original waterways, such as the Inhangá stream, were largely suppressed or channeled, but their valleys can still be perceived in the urban morphology, in the road cuts, and in the layout of the streets. These small watercourses descend from the amphitheater formed by the alignment of the Cantagalo and Pavão-Pavãozinho, Cabritos, Saudade, São João, Babilônia, and Pedra do Leme hills, and formed waterfalls and temporary water veils during rainy periods, functioning as important natural drainage routes down to the beach. The narrow plain squeezed between the sea and these lowered sugarloaf-shaped hills gave rise to one of the densest neighborhoods in the city, the stage for various international and national moments related to carioca and Brazilian culture. Today, highly populated, it manifests itself as a complex amalgam of cosmopolitan diversity and clear social contradictions.
Image description: This is a photograph of a waterfall located in the South Zone. The waterfall is positioned on the left side of the image, with water flowing gently over darkened rocks. On the right, there is an area covered with dense green vegetation, including plants and shrubs. The background features a rock formation with varied textures. In the foreground, there is a calm lake where the water reflects the sunlight. The color of the lake is a beige tone, contrasting with the green vegetation. In the upper right corner of the image, there is text that reads "Relato Oliveira 2022".Cachoeira do Chuveiro
In the area surrounding Lagoa Rodrigo de Freitas, rivers descend from the steep slopes of the Serra da Carioca in beautiful and famous waterfalls until they reach shallow plains before emptying into the brackish lagoon. The largest are the Macacos river, the Rainha river, and the Fonte da Saudade, all with crystal-clear waters that remain relatively well preserved down to their mouths. The Macacos river is among the historic rivers used to supply the city with water, through the Cachoeira dos Macacos dam. Its basin is one of the few where more continuous stretches of forest and crystal-clear flows are still available to the urban eye. The Rainha river, which rises in Parque da Cidade, a protected area, flows well until it meets the urban area, where contamination from domestic sewage already compromises it. The Fonte da Saudade, in turn, is a fast-flowing drainage stream that descends between the Morro do Cabrito and Morro da Saudade hills, and is immediately channeled once it reaches the urban area.
All of these drainages, despite their modest length, are vital as bodies of water that sustain important forest ecosystems along their courses and help maintain the water quality of the Lagoa Rodrigo de Freitas. Because they are polluted, during dry weather, the water management carried out by the city government diverts these drainages into the canal system of the Jockey Clube and Avenida Visconde de Albuquerque, all the way to Leblon beach.
Already in the neighborhood of São Conrado, two small basins are significant and discharge their flows directly into the sea: the Pires River and the Canoas River, one on each end of Gávea beach (the name of the beach in the São Conrado neighborhood). The Pires River converges the flow from the entire Rocinha neighborhood, one of the largest favelas in the world, which occupies almost the entirety of the slopes descending between the Andorinhas and Dois Irmãos hills. This community, with more than seventy thousand inhabitants, has no domestic sewage sanitation, turning the network of channels, drainages, and streams into veritable open-air sewage canals or ones running beneath the cluster of houses. Such a scenario is a shame, for besides directly impacting the Pires River, it expresses the entire history of the absence of housing policy in our municipality, which should indeed be concerned with allowing decent housing for all its residents. The social exclusion of the working class -- worth mentioning, given the minimum significant income needed to live in such a space in Rio's South Zone -- led to the self-construction of these dwellings, leaving this population with precarious conditions.
On the other side, descending from the foothills of Pedra Bonita and Pedra da Gávea, the drainage of the Canoas river plunges abruptly down the rocky cliffs through steep channels until it reaches the timid coastal plain. The entrenched channels demonstrate the power of the flows descending the slopes, with blocks from old avalanches commonly found in its riverbed, the result of successive slope landslides. However, at the mountain's foot, the presence of blocks demonstrating the flow of landslides channeled by the river course did not deter the construction of houses in the small favela known as Vila Canoas. Here too, the excluded working class self-built their homes, and the lack of sanitation contributes to the river pollution of this drainage.
Even so, these Zona Sul basins are examples of small-scale but high-energy hydrographic systems, shaped by the interaction between resistant lithology, abrupt relief, and the moisture brought by winds from the Atlantic coast. Although channeled along their lower courses, their headwaters and upper and middle stretches still preserve the original hydrological logic, protected under conservation units.
