Study of key aspects in simplified modelling of man-made earthen dams breaching: breach shape, erosion process and hydraulics
Francesco Macchione, Gianluca De Lorenzo, Andrea Antonella Graziano
Abstract
The physical process of man-made earthen dams breaching has many aspects that are still poorly understood and under investigation. In this context, dam-breach simplified physically based models are very valuable as they provide quick and accurate solutions that have an application value, although the phenomenon is not yet fully clarified at a theoretical level. This work intends to evaluate the validity and the mutual interaction of the suggested assumptions regarding the following key aspects for a simplified modelling: (1) the geometry of the breach cross-section; (2) the characteristics of the water flow through the breach; (3) the breach erosion law; (4) the morphology of the reservoir. The main findings of this study, in relation to the outlined key aspects, are the following. (1) The breach geometry, assumed of triangular/trapezoidal shape, plays an important role in the computation of the outflow hydrograph, but in this work a dimensionless analysis was performed, from which it was found that there is a low sensitivity region, identified by medium values of a dimensionless parameter which characterizes the dam-reservoir system. (2) The water flow through the breach can be considered in a critical state, with convincing results in terms of numerical reconstruction of the entire discharge hydrographs. (3) The breach erosion law can be related to the mean shear stress of the water flow, by means of a parameter that needs to be calibrated. In this regard, the calibration has been performed choosing a number of historical cases falling in the low sensitivity region identified in point 1, so that the results of the calibration were not affected by the shape assumed for the breach. (4) The morphology of the reservoir affects the evolution of the dam breaching process and, therefore, the shape of the calculated hydrograph; thus, it must be taken into consideration by introducing a level-volume curve into the calculation.