Proposta de uma metodologia para obtenção de parâmetros de brechas em rupturas de barragens em cascata utilizando modelagem física

Abstract

Environmental, economic and social consequences of a dam break are catastrophic. Geometric and breach formation parameters, such as formation time, breach width, breach height and breach lateral slope must be adequately estimated to obtain a rupture hydrograph (duration, shape, volume and peak flow) closest to that one which would occur in case of a real rupture. Therefore, dimensional evaluations are required to properly reproduce breach formation mechanisms adequately. By increasing the representativeness of the consequences estimated, the effectiveness of the respective emergency plan is also increased, reducing associated risks. This research evaluates the hypothetical breach formation parameters specifically for reservoirs which fail in cascade. To determine these parameters, the methodology uses reduced models to simulate the failure of two sequential dams, based on existing dams, to determine the outcoming hydrographs. Outflow hydrographs were determined using hydrological modelling software, considering the breach parameters determined on the reduced model of the cascade reservoirs’ failure. The same simulations were carried out with breach parameters from empirical methodologies available in the literature e.g. MacDonald and Langridge-Monopolis (1984), Von Thun and Gillette (1990) and Froehlich (1987, 1995, 2008). These outflow hydrographs were used as input to a two-dimensional computational hydraulic model, from which the respective flood levels were obtained. By analysis of the parameters of these flood maps, depth, flow velocity, shear stress and hydrodynamic risk, the discrepancies between the breach parameters related to each methodology were evaluated. Results indicated a reduction of 30% on breach formation time and a 40% widening on breach width for the downstream dam. For the tests a standardized synthetic material was developed, replacing the soils.