Author(s): Ninger Kong; Asaad Y. Shamseldin; Bruce W. Melville; Colin N. Whittaker
Linked Author(s): Bruce W. Melville
Keywords: Dual breach erosion; Dam overtopping; Non-cohesive dam; Breach merging; Inflow discharge threshold
Abstract: Due to the increased flood events during the past two decades, the frequency of dam failures caused by overtopping has increased around the world. The significant fatalities and economic losses of these failures highlight the need for understanding the dam breaching process induced by overtopping. Most previous research projects focus on the single breach development on overtopping dam failures, whereas the damage to a failed earthen dam is potentially impacted by the location, size, and number of breaches along the dam crest. The study of multiple breaches has received less attention even though the earth fissures, uneven dam crest level and weak sections (e.g., sluice gate and pipes) could lead to this phenomenon. Compared to single breach evolution, the development of multiple breaches is more complicated and may cause higher damage as large volumes of water simultaneously flow into the downstream area. A series of dual breach dam tests with four different breach separation distances was conducted to systematically study the effects of dual breaches and breach separation distance on the breach erosion. Based on quantitative analysis of the non-cohesive dual breach erosion, three types of breach evolution are observed, namely no breach merging process, spatial breach process with merging and plane breach process with merging. Compared to the single breach model of non-cohesive dams, the inflow discharge threshold of the plane breach erosion increases significantly in the dual breaches model. This result indicates that the model with two breaches has a larger capability to discharge flow than that of the model with a single breach. In the non-cohesive dual breach model, the threshold of the inflow discharge for the plane breach mode increases with an increase of the breach separation distance. However, the threshold stabilises around a constant value (i.e., 20.0 l/s for the presented test setup) once the breach separation distance is longer than four times the dam height. This study improves our understanding of the fundamental mechanisms of dual breach erosion caused by overtopping.
Year: 2023