Rule curve for seasonal increasing of water concessions in reservoirs with low regularized discharges

Abstract

Regions with high hydrological variability are usually supplied by reservoirs that regularize discharges inter-annually, with low discharge of regularization, seasonally subject to large overflow and evaporation losses in their periods of high water levels. The Brazilian semiarid is one of such regions. This work looks at the possibility of using water that would be evaporated and/or spilled, in regions with such characteristics, to supply demands that would not be otherwise provided by the maximum legally allowed withdrawal discharge. The proposed method was applied to the operation of a large reservoir, located in the semiarid region of Brazil. Through simulation of the water budget and optimization, a rule curve was developed for reservoir operation for achieving the maximum exploitable reservoir withdrawal in rainy periods. The results show that it is possible to use the excess water in periods of large inflows with no damage to water supply during dry periods.Keywords: Concession discharge; Reservoir operation; Rule curve. RESUMORegiões com alta variabilidade hidrológica são, geralmente, abastecidas por reservatórios plurianuais com baixas vazões de regularização, sujeitos, sazonalmente, a grandes vertimentos e a perdas por evaporação em seus períodos de cotas altas. O semiárido brasileiro é uma dessas regiões. Este trabalho levanta a hipótese do aproveitamento da água vertida e/ou evaporada, em regiões com estas características, para suprir demandas não atendidas pela vazão outorgável dos reservatórios, utilizando uma vazão máxima excedente para incrementar a vazão outorgável. Como caso de estudo, foi efetuada a operação de um reservatório de grande porte, localizado no semiárido brasileiro. Por meio de simulação do balanço hídrico e otimização, foi desenvolvida uma curva-guia para operação do reservatório e encontrada a vazão excedente máxima explorável em períodos de cheia. Com os resultados encontrados, pode-se concluir que há a possibilidade de utilizar uma vazão excedente em períodos de grandes afluências sem que o abastecimento em períodos secos seja prejudicado.Palavras-chave: Vazão outorgável; Operação de reservatórios; Curva-guia.

Building a System Dynamics Model to Support Water Management: A Case Study of the Semiarid Region in the Brazilian Northeast

“…The population of the region under study consists of approximately 650,000 people with a current and future growth rate of 1%, which was taken into consideration [12]. The cities receiving their water supply from this reservoir face an array of challenges, occurring principally due to hydroclimatic aspects in the Paraíba River region-the main source of the reservoir (Table 1) [13,14]-as well as factors linked to municipal water management (e.g., the high rate of 33% water loss) [15]. The water loss considered in this study was a result of real losses (leaks in pipes) and apparent losses (theft, and hydrometers with calibration problems).…”

“…Another worrying factor was the high average of water consumption that corresponded to approximately 222 L/p/d (liters per person per day) (131 domestic + 91 industrial/other) [16,17], although this index was considerably lower than most industrialized countries [18]. Information concerning inflow and evaporation flux of the Epitácio Pessoa Reservoir, which complements the water balance needed to realize the simulations in this study, was acquired from Nunes et al [14]. Therefore, for inflow, a series of discharges between 2004 and 2015 was employed based on daily volume measurements ( Figure 2).…”

“…Information concerning inflow and evaporation flux of the Epitácio Pessoa Reservoir, which complements the water balance needed to realize the simulations in this study, was acquired from Nunes et al [14]. Therefore, for inflow, a series of discharges between 2004 and 2015 was employed based on daily volume measurements ( Figure 2).…”

“…The series was considered representative due to its proximity to the reservoir, similar weather characteristics, vegetation, and terrain. Coefficients (Kp) calculated by Nunes et al [14] were used to correct the measured values in the Class A tank. In the Epiácio Pessoa Reservoir, coefficients other than the commonly employed value of 0.7 were used seasonally, given that each season of the year brings its own climatic conditions, radiation, humidity, wind, and air temperature, among other attributes associated to the exclusive climate of each locality.…”

“…The Epitácio Pessoa Reservoir is a stock of surface water, being the only supply source for the region delimited in this study. Equation (3) shows the formulation of the water balance adapted to the Epitácio Pessoa Reservoir [14]. All variables were measured using MCM (million cubic meters).…”