Monitoramento e modelagem de um sistema filtro - vala - trincheira de infiltração em escala real
Lucas, Alessandro Hirata
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Infiltration systems aim to reduce the effects of urbanization, waterproofing and runoff, acting at the origin of the runoff. The objective of this project was to monitor a Filter - Swale Trench (FVT) system, built at UFSCar s campus in real scale by retaining the runoff produced by waterproofed areas. The FVT system was built in soil described as sandy loam, with infiltration capacity between 2,30x10-5 and 6,05x10-6 meters/second, and was obtained by doing testes in field using double ring infiltrometer and inverted well, respectively. The FVT system was monitored by measuring the precipitation, the inflow system, the level of water stored, and by verifying that the system functioned during the rainfalls. Sixty rainfalls were monitored, with up to a 48 year return period, with no extravasations. We observed differences between the design and operation of the system, such as the catchment area, the infiltration area and losses in the channel distribution. This shows that the structure is larger than actual scenario. We compared the fine content of the gravel and sand filter and the geotextile s permeability of the infiltration trench, sampled after construction and after about a year of system operation. After the period of operation, the gravel and sand filter showed an average reduction in fine content of 29% and 52%, respectively. The geotextile showed partial clogging, which reduced its permeability by an average of 45%. The system has been modeled using the PULS method and SWMM model. The PULS modeling method allowed us to determine the water storage level satisfactorily. Graphically, the storage level curves are similar, with average values of the Nahs - Sutcliffe coefficient (NS) of 0,43, a mean maximum storage level error of 29% and mean empting time absolute error of 36%, obtained in the validation model. The SWMM model enabled the microbasin simulation to run a Departmento de Medicina bulding and the FVT system performed unsatisfactorily and demonstrated some limitations. The model validation presented absolute mean errors of peak runoff at 58%, accumulated inflow volume of 35%, mean error of the maximum storage level of 72%, mean error of emptying time of 79%, mean NS values of inflow of 0,02 and mean NS values of storage level of - 0,79. Using the SWMM model resulted in lower levels of storage and smaller emptying times than those using the PULS model. The system maintenance summed up in cleaning the land, removing sediments from the measurement channel, and performing gardening services. The system maintenance cost in the first year of operation was R$ 85,00 / month or R$ 0,67 for each square foot of impervious drained area, considered high compared to maintenance costs of conventional drainage systems.