Coeficiente de extravasamento calculado em base mensal para reservatórios de aproveitamento de águas pluviais em municípios brasileiros

Abstract

Water is a vital resource for human life, with the world's population increasing its water consumption also increases, especially in large urban centers. Therefore, alternatives to the rational consumption of treated water are sought, highlighting concrete and economically viable projects. The objective of this work is to determine the extravasation coefficient for rainwater harvesting systems using the Ripple method, which is generally used to measure the volume of the rainwater harvesting system reservoir and is obtained through historical series of daily rains or monthly. The coefficient of extravasation is given by the ratio between the volume of water used, on a daily basis, and that on a monthly basis, with the function of correcting the volumes of the accumulation reservoirs calculated for a new volume of rainwater used more precise, being presented monthly or annually. In order to obtain the Extravasation Coefficient, daily rainfall series were used in a continuous period of 30 years (1984 to 2013), obtained from INMET and ANA for 5 Brazilian municipalities (Brasília-DF, Curitiba-PR, Manaus-AM, Quixeramobim CE and Recife-PE). The volumes of the reservoirs (40, 30, 20, 15, 10 and 5m³), the Runoff coefficient values (0.85 and 0.90) were pre-established and divided into 3 distinct patterns of water consumption in the residence and size of the catchment area (Popular, Medium, and High). Using the daily and monthly Ripple method, one can find the Monthly Extravasation Coefficient for all years included in the study, so the EC value for each month will be determined by the average of that month, throughout the study period. 18 graphs of the extravasation coefficients were obtained for each city, relating the reservoir volumes to the catchment and consumption areas of each residence pattern, where three were found, with the two Runoff coefficients. With these graphs, it became possible to use historical monthly rainfall series, correcting monthly values of the volumes obtained using the monthly Ripple method, reaching values close to the values obtained in the daily Ripple method, resulting in better-sized reservoirs that have greater annual volumes of water. The case study used monthly 10-year rainfall series from the city of Joao Pessoa-PB, withdrawn from INMET and studied conditions to demonstrate the effect when using the coefficient of extravasation in the design of the rainwater reservoir. The difference between the volume of water used using Ripple with the EC is approximately 1.24% or 2.10m³ (2100 liters) higher each year, in the total volume overflowed, the difference is 6.67% lower. With these results presented, it is possible to conclude a more precise estimate of the volume of rainwater used, in relation to the use of only the monthly means of precipitation in the design. This higher precision provides more realistic values of the amount of water used and the economic viability analysis of the alternative.