Análise experimental em modelo físico de estruturas hidráulicas de remoção de sedimentos em barragens: descarregadores de fundo

Abstract

Bottom outlets are hydraulic structures present in a large number of small and medium size dams, essential for sediment removal in these enterprises. They are incorporated to the upstream facing and in the lower portion of the useful volume of the reservoirs in order to increase the water storage capacity and the useful life of the enterprise in question. The operation of the bottom outlets occurs through the removal of sediment by the dragging capacity of the flow, being the phenomenon of silting, originating from anthropic and natural activities of the hydrographic basins, a gradual process inherent to the different uses of water reservation. In several places around the world, due to its importance, are being developed different methodologies of dimensional analysis and estimation of the cone of sediment removal deposited in reservoirs considering the limited efficiency of the bottom outlet structures. In this way, the present work aims to experimentally identify the hydrodynamic behavior of the bottom outlets and their main hydraulic and sedimentological parameters that favor the removal of unconsolidated bottom sediments. Three distinctive physical-experimental models were used with different geometry characteristics proposed for the dischargers, assay flows and hydraulic load under these structures, having been evaluated the new bottom conformations in 4 (four) different types of materials: sand, processed rubber, Cardiff coal and CATA coal. Through the bathymetric profiles, extracted after the activation of the removal structures, new dimensionless parameters were developed that estimate the reach and maximum width of the removal cone representative of the desilting process of the reservoirs under Pressure Flushing conditions. In addition, were verified the estimates defined in literature by Meshkatiet al. (2010a) and (2010b), Meshkati et al. (2010) in Emamgholizadeh et al. (2013), Fathi-Moghadam et al. (2010) and Emamgholizadeh and Fathi-Moghadam (2014), for the maximum dimensions of the removal cone, as well as the maximum volume of sediments removed. The dimensionless of estimate depth ( ), length ( ) and width ( ) maximum presented good correlations when applied to the results obtained from the essays performed in the 3 (three) models analyzed, within the dispersion usually verified in sediment studies, being the characteristics of the particles one of the most important parameters for the future applicability of the dimensionless in scale of prototype.