Planning and Design of Urban Flood Control Measures: Assessing Effects Combination

Different approaches related with urban flood problems treatment are evolving and there is a large set of possible engineering measures that can be applied. Lately, the traditional approach, focusing on improving channel conveyance, is being complemented by distributed structural measures and nonstructural measures, considering the basin under a systemic point of view and aiming to recover natural flow patterns prior to urbanization. In this context, it becomes necessary to evaluate the potential use of different combinations of the possible interventions, in such a way that the efficacy of these sets in terms of flood mitigation can be optimized. This kind of analysis is of crucial importance and involves technical and economic aspects. Combined effects of the chosen measures may produce a result that is not equivalent to what would be expected from the summation of its individual effects. The systemic behavior of an urban watershed, especially when the drainage system works jointly with flooded urban landscape elements, makes it possible that some design solutions become to act in a noneffective way. Sometimes, different interventions just superimpose concurrent results. On the other hand, it is possible to generate better results, with extra benefits, when proposing adequate combinations capable to join efforts. Mathematical models may act as valuable tools that are able to simulate floods in complex urban watersheds and provide an integrated assessment capability. In this context, mathematical models can evaluate the efficacy of flood control measures sets. In this paper, a mathematical model, based on the flow cell concept, was applied to study the use of a wide range of different flood control measures in the Joana River watershed, located at the northern region of Rio de Janeiro City, Brazil. This model is composed by a hydrodynamic core that works together with a distributed hydrologic model. According to the achieved results, it is possible to notice that distributed detention reservoirs—located at upstream reaches, parks and public squares, and also at urban sites—are very important flood control alternatives. It is also noticed that reforestation of slope areas, although some of which are nowadays occupied by lower income communities, is a desirable alternative. Finally, it must be stressed that even traditional flood control measures, presently avoided in many design situations as they may transfer downstream inundation problems, can be important in an integrated flood control project, if adequately combined with other measures.