The watershed basins of the Baixada de Jacarepaguá make up one of the most extensive and complex drainage systems in the city of Rio de Janeiro. Nestled between the foothills of the Maciço da Tijuca to the east and the extensive Maciço da Pedra Branca to the west, these basins outline a broad coastal plain shaped over time by fluvial and marine processes — where rivers, lagoons, and channels intertwine in a delicate network of water and sediment.
Important rivers flow down from the Maciço da Tijuca, especially from its northern and western slopes, from the Floresta da Tijuca to the neighborhoods of Freguesia and Anil, all the way to Gardênia Azul. Three rivers -- Olho D'água, Fortaleza, and Ciganos -- come together to feed the Sangrador river's drainage in a single channel that collects the runoff descending from the northern face of Pico da Tijuca. Worth noting is the Ciganos dam, built there to supply the city with water. Just on the western slope of the Maciço da Tijuca, descending from Bico do Papagaio, the Cantagalo, Quitite, and Papagaio rivers flow, one after another, in cascades until they reach the sedimentary lowlands. All these rivers have their headwaters within protected areas of the Parque Nacional da Tijuca, ensuring pure, crystal-clear sources. Once again, upon reaching the urbanized lowlands in the neighborhoods mentioned, the rivers are channeled and polluted, flowing through the main channels of Anil and Arroio Fundo until they reach the Lagoa da Tijuca. This same lagoon body also receives, further downstream, the rio das Pedras -- with a well-known community at its mouth --, the small Muzema river, and the important Cachoeira river, which comes down along the main axis of the Maciço da Tijuca in cascades, running alongside the Estrada de Furnas. The Cachoeira river deserves further comment, as it contains the two largest waterfalls in the Maciço da Tijuca: the Cascatinha Taunay, in the heart of the Parque Nacional da Tijuca, and the Cachoeira Grande da Tijuca, once an area for recreation and swimming, now polluted, near Furnas de Agassiz -- a former geological attraction of the Floresta da Tijuca that today is little explored by public management.
Image description: This is a photograph of a waterfall in the middle of a forest. On the left, we see green plants and shrubs, while on the right there are large rocks covered in green moss. The center of the image highlights a small waterfall cascading over these rocks, forming a small pool at the base. The ground is made up of stones and soil, with some dry branches scattered about. The natural lighting creates interesting shadows on the rocks and the pool.Baronesa Waterfall, in the Floresta da Tijuca (PNT-ICMBio), Rio Cachoeira
All these drainages do not escape the same pattern, imposed by the fractures, faults and planes of weakness of the geological bedrock, draining water from the fissure aquifers that increase the volume of water downstream until they reach the plain. This, in turn, densely urbanized and paved, frequently suffers from flooding problems.
On the opposite side, in the Maciço da Pedra Branca, a series of vigorous rivers originate from high headwaters on steep slopes, descending in sequences of waterfalls, rapids and small cascades through environments that are also forests protected by the Parque Estadual da Pedra Branca. These are: the Grande river and the Arroio Pavuna, collecting the waters of the eastern slope of the Maciço da Pedra Branca.
Further to the southeast, the Rio do Camorim basin stands out. Confined within a suspended valley, its course reflects the resistance of the rocks and the steep slope, creating a narrow fluvial passage that was used to build a reservoir. This dam has historical and ecological importance, having once supplied colonial mills and still being used today as a water source in the Camorim and Vargem Pequena region.
These rivers flow through deep valleys and directly feed the Jacarepaguá lagoon and its connection to the Tijuca lagoon, forming the lagoon complex of the Baixada de Jacarepaguá, which are joined by the Curicica marsh systems and, further on, only through the water table, by the Marapendi lagoon. In this transition from the mountains to the plain, a change in the river regime can be observed: from the rapids and waterfalls of the mountainous stretch to the meanders, marshes, and wetlands of the lowlands, where drainage becomes slower and influenced by the high level of the water table and the tide.
The plain of the Baixada de Jacarepaguá is, therefore, the product of the encounter between the energy of the mountain massifs and the marine-lagoon environment of the coastal plain. This plain was formed by fluvial and marine sedimentation, creating low-lying, poorly drained terrain, rich in organic matter and highly sensitive to the impermeabilization caused by recent urbanization.
Image description: This is a photograph of a waterfall in the midst of a dense forest. On the left side, we see vibrant green vegetation, while on the right, water flows gently over darkened rocks. At the center, the waterfall splits into two parts, with droplets of water spraying across the rock. The background features more rocks and vegetation, creating a natural and serene setting.Waterfall on the Camorim River, just below the Camorim Dam
The southern slope of the Maciço da Pedra Branca brings together one of the region's most abundant drainage networks, forming an expressive system of wetlands, known by the names of the neighborhoods of Vargem Grande and Vargem Pequena. As a toponymy remaining from its hydrological functionality, what is expected is, without a doubt, extensive floodplains, with marsh systems and old swamp forests, of which rare examples remain.
The vargens (lowland plains) are expressed at the foot of the massif that gathers rivers flowing down as sequential waterfalls of crystalline waters beneath a forest environment. From the Sacarrão river to the Cabungui and Morgado, the drainages add up to feed the Canal do Rio Morto, laid out in a straight line to the sea by the works of DNOS (the former Departamento Nacional de Obras de Saneamento) in the early 20th century. In fact, the entire vargem is cut through by a sequence of straight canals that also collect the flows coming from the alignment of the Serra de Guaratiba, all the way to the Vale do Rio Piabas.
Image description: This is an aerial photograph of an urban area overlooking the sea. On the left side, we see an extensive stretch of buildings and green areas extending to the horizon, where the sea is visible. Moving to the right, we notice a series of mountains that form a natural arc. The sky is clear blue with a few scattered clouds.Sernambetiba Canal that artificially drains Vargem Grande
Image description: This is an aerial photograph of a coastal beach. On the left side, there is a road running parallel to the coastline, surrounded by dense green vegetation. Moving toward the right, we see a strip of sand extending toward the sea. In the central part of the beach, there are buildings and a small recreational center with a large concrete ring. On the right, the sea shows waves breaking on the sand, with colors ranging from light green to dark blue.Mouth of the Sernambetiba Canal
The waterfalls that flow down from the massifs, once central to daily life and the local imagination — places for bathing, resting, and connecting with the forest — now survive as ecological refuges within the boundaries of Pedra Branca Park and the surrounding protected areas. They are watermarks of the city's deep geography, carrying living memories of territories that passed through slavery, charcoal production, and agriculture.
With the accelerated urban expansion in recent decades, many of the rivers were channeled or straightened, radically altering the hydrological functioning of the region. Complaining about the floods in this region will be the recurring theme of future news reports.
Image description: This is a photograph of a cityscape during sunset. On the left side, we see a darkened area, possibly a mountain or cliff. In the center, the city is lit up with yellow and red lights, creating a contrast with the sky. On the right, there is a large mass of low clouds covering much of the city. The horizon is tinged with orange and blue, indicating that the sun is setting.Sandy strip of Barra da Tijuca, densely occupied after the 1980s, on a beautiful evening.
