Morfometria, compartimentação e hidrodinâmica de um reservatório periurbano tropical: prognósticos sobre o tempo de vida útil do Reservatório de Vargem das Flores, Minas Gerais Brasil

Abstract

This study was conducted in an urban reservoir, in the metropolitan region of Belo Horizonte (BHMA), MG - Brazil, Vargem das Flores Reservoir. The major objectives of this investigation were: (a) conducting a morphometric study with an identification of sources of siltation in the catchment basin and delivering a new bathymetry inventory of the reservoir; (b) performing a limnological study, with a focus on water quality, characterization of the trophic level of the reservoir and in proposing a model of limnological compartiments, based on physical and chemical parameters of the water; (c) investigating the role of hydrodynamics (residence time and wind forcing) on the horizontal distribution of planktonic organisms. The Vargem das Flores reservoir was selected because it is one of the most important sources of water supply for the metropolitan area of Belo Horizonte. Neverthless, the reservoir has been threatened by different human activities in its basin. It also has a history of cyanobacterial blooms. Morphometric characterization is obtained by performing a new bathymetry, using an echo sounder SonarLite (Ohmnex Ltd.), coupled to a D-GPS (Differential Global Positioning System) to obtain the geographical coordinates of each measured depth. The limnological characterization of the ecosystem was studied with emphasis on the horizontal variation of several variables used for the typology of water quality in reservoirs. For generation of the hydrodynamic model, the SisBAHIA software was used, it was also used in generating the residence time of water. The present investigation estimated areas and volumes considerable different than existing data from the literature. According to our new estimates, Vargem das Flores reservoir is a small reservoir with an area of 5.15 x106m ² and volume of 29x106 m³, with relative depth (Zr = 0.83%). In the last decade, the reservoir has experienced an extraordinary increase in sedimentation rates. In just nine years, it has received the same amount of sediment as it has received in its first 28 years of operation. The rate of sedimentation increased about 2.5 times, thus, reducing its useful life time equally. The study of longitudinal variation of limnological parameters showed that the reservoir is eutrophic and its water quality varies strongly according the different horizontal compartments. Finally, this study showed that the horizontal distribution of zooplankton and phytoplankton were associated with hydrodynamics and local pulses of nutrient and suspended solids.