Proposal of coefficients for performance analysis of reservoirs for rainwater storage

Abstract

In Brazil, the existing regional disparity in water availability makes it essential to search for alternative solutions that guarantee the supply complies with water quality parameters, affordable cost and adaptation to local conditions and needs. Rainwater may satisfy these requirements. The existence, however, of numerous methods for sizing the reservoir of the system adds some subjectivity to the calculation of the storage volume and can lead to the determination of a storage value that does not meet the project's needs. In this context, this work aims to propose two coefficients, the Volumetric Idleness Coefficient (VIC) and the Volumetric Overflow Coefficient (VOC), which can be used as criteria for determining optimal volumes of reservoirs for rainwater storage. To this end, we considered three reservoir sizing methodologies, already existing in the literature, in different scenarios of catchment area and demand, with data from daily rainfall series of 37 years throughout the Brazilian territory. Additionally, an algorithm in Python was developed to obtain the values of these coefficients for the selected reservoir sizing methods for any point in Brazil, considering different scenarios of catchment area and demand. Results showed that the rainfall characteristics influence the values obtained for VIC and VOC, especially when the reservoirs are sized by a method that considers a water balance. Furthermore, an increase in demand in the catchment area causes a decrease in the values of both coefficients. Both coefficients presented in this article can be applied as reservoir sizing criteria through the comparative analysis between different sizing methods within a scenario since the method that allows a minimum coefficient is associated with an optimal reservoir volume, either for the project that aims to maximize the use of the useful storage volume (VIC) or maximize the use of the volume of water captured by the system (VOC).