Hydrological methodologies analysis to obtaining ecological and grantable flows, considering annual and monthly criteria for Doce river, Brazil

Abstract

Grant is the National Water Resources Policy legal instrument responsible for guaranteeing water to meet human needs and maintain aquatic life. However, attention should be paid to the method used to obtain grantable volumes, as they are determined through minimum flows on an annual basis studies. This study aims to comparatively analyze methodologies for determining grantable and ecological flows and, seasonality influence in obtaining them for Doce river water regime, Southeast Brazil. Seasonal component was identified by frequency analysis. Log-Pearson type III distribution was the one that best fit the data. Considering 50% of the monthly Q7,10, it is possible to increase the grantable volume in every month, while, for 50% of Q90 and 70% of Q95 criteria, there is a decrease in the volume subject to granting between July and October. The currently method adopted in the basin, 70% of the annual Q95, presents ecological flows lowest values and, in September month, allows granting a volume 21% greater when compared to the monthly basis. It is concluded that ecological and grantable flows determination considering seasonal characteristic allows a better management of the studied watercourse.