Real-Time and Forecasted Flood Inundation Extents in Sao Paulo, Brazil

Floods are natural events that can cause victims and various social and economic losses. These events are originated from intense rainfall that exceeds soil infiltration capacity leading to major water runoff that surpasses the capacity of drainage systems causing flooding and overflows. In particular, at highly urbanized basins, the problem becomes even more complex since it involves land use issues, not only by raised flood peaks caused by broadened impervious surface areas, but also by increased vulnerability to flooding due to highest population densities located in flood prone areas. Yet there are frequent cases when the impacts of these floods are aggravated by lack of consistent information, which implies poorly conceived projects, bad maintenance and faulty decisions by public officials, investors and society in general.

Based on this scenario, the São Paulo City Hall (PMSP) has invested in a flood management system centered on a system for evaluation, monitoring, forecasting and warning in order to promote stormwater management efficiency and effectiveness of preventive and corrective actions. Therefore, PMSP maintains a technical assistance contract with the Hydraulics Technology Center Foundation (FCTH). This partnership addresses activities of atmospheric monitoring of precipitation using radar and also land precipitation monitoring, as well as channel and reservoir levels through telemetric network, weather forecast, outflow and flood prediction in critical watersheds and supervision of major drainage structures performance, in order to support the management of the impacts of hydrological events.

A more detailed treatment is given to five municipal watersheds: Aricanduva, Água Espraiada, Cabuçu de Baixo, Mandaqui and Morro do S, and to the Pirajuçara basin, which also lies in the municipalities of Taboão da Serra and Embu. The developed system allows fast access to subcatchment data and grants models that simulate conditions of flooding risk in advance so that preventive or contingency measures can be taken. Rainfall data and prediction are obtained, processed and disclosed by the Flooding Alert System of São Paulo (SAISP) that operates Meteorological Radar that belongs to Department of Water and Energy of the State of São Paulo (DAEE) as well as over 200 telemetric stations responsible for the collection and transmission of water depth and rainfall data, and the rain forecast is taken every 10 minutes to a prediction horizon of 3 hours.

Hydrological modeling of the subcatchments and hydraulic modeling of the main channels were performed employing PCSWMM. Watershed calibrated projects for extreme events are available to PMSP specialists so they can evaluate and carry out new projects. In addition, there is a version of PCSWMM Real-Time disclosing prediction results for flood inundation sites addressed to the Emergency Management Center (CGE) in real time on the internet, with an intuitive graphical web-interface, easily allowing access to information and analysis of complex problems by technicians.