Predicting floods from urban development scenarios: case study of the Dilúvio Basin, Porto Alegre, Brazil

It is well known that urbanization increases the hydrograph peak and overland flow volume from drainage basins, and that the concentration time of flood flows is diminished. To predict the effects of future urban development on the flood regime, the design hydrograph must be estimated. Nevertheless, the information from which to estimate a design hydrograph is limited where planning procedures (such as the `Urban Master Plan' of some Brazilian cities) specify only the type of urban land use (residential, industrial, etc.) and the recommended population density in areas where development is planned. This paper presents the relationship between parameters of a hydrologic model and urban development characteristics as set out in the Urban Master Plan. A hydrologic model IPH IV [C. E. M. Tucci, B. Braga, A. L. L. Silveira, RBE Caderno de Recursos Hı́dricos 7 (1) (1989)] was used together with a GIS to predict the hydrograph corresponding to alternative urbanization scenarios. Model parameters were fitted and verified using recorded data from the Dilúvio Creek in Porto Alegre, Brazil. The model was applied to predict the design hydrograph for different risks in accordance with the city's Urban Master Plan. Flooded areas corresponding to a storm rainfall with return period 25 years were calculated by simulation, the flooding being mainly due to flow obstruction by bridges.