Ferramentas para a determinação de vazões ecológicas em trechos de vazão reduzida: destaque para aplicação do método do perímetro molhado no caso de Capim Branco I

Abstract

For the best management of the water resources, professionals of different knowledge areas have investigated the water courses characteristics. One of the goals of these studies is to establish minimal flows: the amount of water that must remain in the stream bed after thewater diversion for multiple purposes such as irrigation, industrial and public supplying, generation of power, etc. This flow is denominated minimal, residual, environmental or ecological. The establishing of a value for the minimal flow involves defining, taking in account thecharacteristics of the rivers, the necessary amount of water for maintenance of the aquatic biota. Many methods have been used based on hydraulic, hydrologic, habitats classification, holistic approaches and others parameters. Some of these methods intend to maintain satisfactory water quality downstream, without any biological analysis.The present work aims to analyze the different methods for minimal flow determination described in literature, focusing on the Wet Perimeter methodology. This method is based on hydraulic criteria linked to the availability of habitats for the aquatic fauna. The method wasapplied to the stretch between the powerhouse and the dam of the Capim Branco Power Plant - AHECB I. Initialy, a bibliographical revision was carried out on the methods of estimating minimal flows, detaching advantages and disadvantages of each one. For the application of the Wet Perimeter Method, the computational program HEC RAS was applied. The relation between the wet perimeter and the flow was estimated for 37 river sections. The results have show that the wet perimeter method defines bigger minimal flows values, than the usualy employed methods, such as the Tennant and the Permanence curve methods. A tentative to correlate fish abundance and wet perimeter was also made, using recent fish samples and the estimated values of wet perimeter.