Evolution of Dam Breach and Routing of the Flood Waves at the Downstream Reaches

Abstract

Historical failure of dams and then impact on the environment created immense disaster in terms of loss of human life and property. A disaster is associated with risk and therefore needs a thorough investigation for its possible outcomes and safeguards. Therefore, study of risk associated with each dam is becoming an important activity to prevent and mitigate the consequences of its failure. To understand the dam break process, many researchers have investigated the work by using distorted physical model, numerical simulations or experimental coupled with numerical based approaches. To quantify the risk associated with dam break, one needs to understand the breaching process that leads to predict breaching parameters. This research is focused on three main objectives, empirical equations are proposed for estimation of breach parameters and peak outflows by using data of past dam failures. It is known fact that the resultant flooding at the downstream reaches due to an overtopping failure of the earthen dam is reliant on breach formation process and the erosion rate of compacted soil. Therefore, the second objective is to carry out the overtopping failure of 22 embankments that are experimentally investigated that are constructed with different soil properties, compaction moisture content and compaction energy. The purpose is to understand, how these breach parameters are affected by the change of soil properties, compaction moisture content and compaction energy. The final breach shape and parameters recorded in the experiments show remarkable change for each failure. The results testify a high correlation between compaction moisture content with the erosion process. Also, the effect of embankment cracks on over topping breach failure is studied. It is seen that embankments with large dry density erode faster as compared to the embankment with low dry density because of the developments of deep and long cracks in the former. Further, MIKE 11 (1-D) hydrodynamic model is used to estimate the consequences of over topping breach failure for four earthen dams in the Brahmani River besin in term of water levels, travel time of flood waves, flow velocities and flood inundation. The dams included in this study are Mandira, Kansbhal, Pitamahal, and Rukura. Location of these dams is such that release of water from these dams directly affects the flow in Brahmani River, leading to Rengali dam. For this analysis, breach equations developed in the present study is used to predict the breach parameters. Failure of these dams shows sudden rise in flow and water level at Brahmani River that gives rise to dangerous situation at the downstream coastal areas. Further, the Rengali dam gate operation and its impact on downstream areas are also investigated. The flood inundation maps are prepared and presented which helps in making the emergency action plan for dam break scenarios.