Avaliação de práticas de desenvolvimento de baixo impacto (LID) em sistema de drenagem sob simulação temporal contínua

Abstract

Due to the growth of urbanized areas, there is a significant change in the use and occupation of the land in the watersheds, which alters their hydrological responses to rainfall events. Among these changes, we can mention the reduction of water infiltration into the soil, an increase in the speed and volume of surface runoff, and a reduction in the watershed concentration time, which generates higher surface runoff peaks. For rainwater management in urban areas, it is common to employ stormwater drainage systems. However, to ensure that the increase in the surface runoff flow rate to be drained, or the hydraulic efficiency reduction that occurs over time, does not make them obsolete, drainage systems require expensive expansions, which increases their maintenance and operation costs. In this sense, Low Impact Development (LID) practices have been widely used to prevent stormwater drainage systems’ obsolescence by mitigating surface runoff. Several previous studies have proven LID practices efficiency in reducing surface runoff in urban watersheds, however, the LIDs spatial distribution within the watershed, which may alter its efficiency, has not yet been sufficiently analyzed under continuous temporal simulation, which can increase the simulation representativeness and accuracy. Thus, the present study simulated, for the stormwater drainage system of part of the urbanized area of the Universidade Federal de Lavras Campus, under a continuous rainfall time series of 2 years, the impact of the implementation of five LID practices (bioretention cell, rain garden, infiltration trench, permeable pavement and vegetated swale), as well as combinations between them, employing four LID placement strategies (downstream, center, upstream, and uniformly). Also, for the most efficient placement strategy, the implementation of these LID practices was evaluated, acting individually, in four implemented area percentages (10, 15, 20, and 25% of the impervious area). Under the analyzed conditions, it was found that, for the same placement strategy, except for the vegetated swale, the capacity of LID practices to reduce flow rate, peak flow rate, and flood volume do not differ under rainfalls with low return period. Also, for rainfalls with a low return period, the implemented LID increase is not proportional to the percentage reductions of the variables evaluated. The LID practices placed following the uniform strategy proved to be more efficient, but, on the other hand, in places where there were higher values of conductivity, the center strategy obtained better performance. Despite the significant reduction in the flood volume, LID practices implementation has not been able to completely prevent its occurrence. Thus, it is essential to associate LID practices with conventional drainage methods for urban flood management.