Disponibilidade hídrica da região hidrográfica dos sertões de Crateús: a regularização de vazões por reservatórios estratégicos

Abstract

The state of Ceará is geographically located in an intertropical zone of the planet. Among the main characteristics of this zone are the seasonality of the rains and the intense solar incidence, which results in two hydrologically distinct seasons, one rainy and the other dry, in addition to high evaporation rates during the year. The region, located in the crystalline basement, is characterized by shallow and compact soils, favoring the formation of intermittent and ephemeral rivers. Thus, natural surface waters are insufficient to meet the demands, making it necessary to build artificial surface reservoirs in order to increase water availability, in terms of regularized flows. The present work has as general objective to determine the regularized flows, with different levels of guarantee, for 11 strategic reservoirs of the Hydrographic Region of backlands de Crateús (RHSC), in addition to the impact on the flow regularization capacity of the integrated systems of reservoirs in series. The simulation of the operation of the reservoirs was carried out using the SIMRES hydrological model. To this end, the reservoirs were classified into two groups according to the existence of strategic reservoirs in their hydrographic basin. The group without the presence of an upstream reservoir was simulated in parallel. For those with upstream reservoirs, two types of simulations were performed, one in parallel, considering their natural watershed, and another in series, considering the cascade reservoirs as a water system. It was found that the RHSC has the capacity to regulate a flow of 218.5 l/s, with 90% guarantee, disregarding the Fronteiras reservoir (still under construction), with 78% of this flow corresponding to the sum of three reservoirs: Carnaubal, Barra Velha and the Barragem do Batalhão. With Fronteiras, the total regularization flow of the RHSC will be 2,358.5 l/s, for a 90% guarantee. This was the only one to have a flow regulation capacity with 100% guarantee. As a result of the simulations, it was possible to verify the efficiency of the reservoirs through the water balance, relating the inflows with the values of the outflows in regularized, poured and evaporated plots, where two were extremely inefficient, four inefficient, four efficient and one extremely efficient. Regarding the impact on the flow regulation capacity in integrated systems, two of the reservoirs present losses in relation to the hypothesis of the existence of only the main reservoir, and two present gains in the flow regulation capacities when operated together.