Diversion Tunnel for Flood Control in Rio De Janeiro, Joana River Watershed (PAP014740)
Aluisio Pardo Canholi, Melissa Cristina Pereira Graciosa, Ruy Juji Kubota, Marcelo Vidal, Claudia Maria Miranda de Andrade
Flood risk management in mega cities
Joana River, in Rio de Janeiro, Brazil, and its exutory watercourse, Maracanã River, are responsible for most of floods that occur in Canal do Mangue watershed, a frequent inundation region in the city. The structural solution adopted for flood control in this watershed were planned in the context of Rio de Janeiro Urban Drainage Masterplan - PDMAP (2013), and encompasses detention basins, channel enlargement and a diversion tunnel with 38 m² cross section, for the transportation of 100 m³/s, which concept and design criteria are hereby presented. Canal do Mangue watershed, with its 45 km² of drainage area, encompasses Rio de Janeiro downtown and many important urban elements of the city, such as Maracanã stadium, the Carnival center Marquês de Sapucaí, the City Hall and Bandeira Square, an important transportation axis that connects south and north regions of the city. Every year floods cause several damage and disruption on traffic, commerce and public services. Canal do Mangue is an artificial channel, built in the 1850's for draining a large mangrove area, in order to enable urban development. This place, nowadays encloses Rio de Janeiro harbor. All the rivers of the watershed, that previously flew to Guanabara Bay, had their exutory changed to Mangue Channel. This concentration of flow has deeply changed the hydrological behavior of the watershed, with several consequences on urban drainage and flood occurrence. The main goal of the proposed structural facilities for flood control in Canal do Mangue watershed was to decentralize the flow. Thus, a diversion of Joana River was planned, through a tunnel that could change its course back to Guanabara Bay. Detention basins were also planned in the upper part of the watershed, in order to guarantee the transportation of the 25-years flood. It has been decided to adopt the NATM (New Austrian Tunneling Method) tunnel construction methodology, that integrates the principles of the behaviour of rock masses under load and monitoring the performance of underground construction during construction, due to: the large needed cross section (38m²); the topographical conditions (great range of tunnel coverings); the geological conditions of the sites crossed by the tunnel that implied different sections to be perforated in both soil and rock sections and the workableness to make the site adjustment of the tunnel treatments (like the horizontal deep drains, jet grouting injections) and on the excavation progress velocity. At the small tunnel covering trenches (in soil), it has been necessary to consider other design adjustments as under a railway existing track, (construction of 2 single tunnels), and under the Bartolomeu de Gusmão and Brasil Avenues (special treatments with jet grouting columns) that aimed to reduce the settlements and stabilizing the tunnel excavation front. Besides, under the railway, it has been planned to start up the works with a tunnel pilot (smaller diameter) to be further involved by the entire final section.