Structural Alternatives for Flood Control in the City of Tubarão, Southern Brazil

Historically the city of Tubarão (Santa Catarina State, Brazil), located in the Tubarão River Basin, has suffered losses for society and public infrastructure due to floods. Seeking alternatives to minimize the impacts of urban floods, structural control alternatives were proposed as part of the Drainage Master Plan for the city of Tubarão-SC.

The model SWMM 5.1 was applied for simulations of the different scenarios of the drainage network. The elements of the drainage network were obtained from the public management, including indications of areas suitable for implementation of detention basins. The urban area was divided into 39 sub-catchments, based on the existing drainage network. All the simulations were developed using a 24-hour duration rainfall with 25-years return period, calculated by the local IDF curve.

Three development scenarios were simulated in this research. The proposed scenarios comprised different structural measures and , in accordance to the urban expansion proposed by the Urban Development Master Plan. The scenarios established for evaluation were: (i) S1 – enlargement of the drainage network to convey runoff with 25-years return period; (ii) S2 – enlargement of the drainage network to convey runoff with 10-years return period, combined with detention basins located according to the availability of area in the sub-catchment, allowing capacity to control runoff with 25-years return period; and (iii) S3 – optimized scenario, combining the alternatives S1 and S2, with the selection of the best economic choice (S1 or S2) for each of the 39 sub-catchments.

The estimated total value for implementation of the three scenarios were very similar, with a 3 % difference between the costs for the most and the last expensive alternatives (S1 and S3, respectively). An important note is that, as the areas for detention were available and had no cost, it may increase cost for control by detention measures. Also, the high estimated total costs point out to the importance of includingnon-structural measures such as source control, for example.