Dimensionless Assessment Method of Landslide Dam Formation Caused by Tributary Debris Flow Events

Abstract

In this study, we develop a dimensionless assessment method to evaluate landslide dam formation by considering the relationship between the run-out distance of a tributary debris flow and the width of the main stream, deposition thickness of the tributary debris flow, and the water depth of the main stream. Based on the theory of debris flow run-out distance and fan formation, landslide dam formation may result from a tributary debris flow as a result of two concurrent formation processes: (1) the runout distance of the tributary debris flow must be greater than the width of the main stream, and (2) the minimum deposition thickness of the tributary debris flow must be higher than the in situ water depth of the main stream. At the confluence, one of four types of depositional scenarios may result: (1) the tributary debris flow enters into the main stream and forms a landslide dam; (2) the tributary debris flow enters into the main stream but overflow occurs, thus preventing complete blockage of the main stream; (3) the tributary debris flow enters into the main stream, does not reach the far bank, and sediment remains partially above the water elevation of the main stream; or (4) the tributary debris flow enters into the main stream, does not reach the far bank, and sediment is fully submerged in the main stream. This method was applied to the analysis of 11 tributary debris flow events during Typhoon Morakot, and the results indicate that the dimensionless assessment method can be used to estimate potential areas of landslide dam formation caused by tributary debris flows. Based on this method, government authorities can determine potential areas of landslide dam formation caused by debris flows and mitigate possible disasters accordingly through a properly prepared response plan, especially for early identification.

Influence of Internal Structure on Breaking Process of Short-Lived Landslide Dams

“…Through analysis, an empirical formula to evaluate the breaking form of the landslide dam on the spot was presented, the relationship between the growth rate of the dam breach area and the growth rate of the saturation degree, and the final dam breach area and the final saturation degree were proposed, as well as the mechanism of the moment when the peak flow occurs was found. Combined with early identification of highrisk areas of landslide dam and life prediction of landslide dam (Chen et al, 2019a;Chen et al, 2019b;Nian et al, 2020), the pre-burst disaster assessment of the short-lived landslide dams could be more effective.…”

Deposition characteristics of debris flows in a lateral flume considering upstream entrainment

“…Debris flow injections from gullies into a river generate sediment deposits which can create a significant degree of obstruction of the river section or even a debris dam (Dong et al, 2011;Tang et al, 2011a;Ni et al, 2014;Liu et al, 2014;Shi et al, 2018;Peng et al, 2021;Zheng et al, 2021). The morphology and hydraulic regime of a river are disrupted during the deposition process and a specific type of disruption is the formation of a deposit lobe (Peng and Zhang, 2013;Chen et al, 2019). The deposition characteristics and features of debris flows in a river are far from being understood due to the complexity of the interactions between the incoming solidliquid mixture conveyed by the debris flow and the receiving river.…”

“…The influences of confluence angle, tributary slope, and debris-flow density on the formation process of a deposit lobe have been analyzed. Three blockage types -complete, partial and submersed blockages can be distinguished from the momentum ratio between flows in the tributary and the mainstream (Dang et al, 2009;Chen et al, 2019). Nevertheless, the effect of the water depth in the lateral flume on the deposit morphology has rarely been investigated .…”

Engineering Planning Method and Control Modes for Debris Flow Disasters in Scenic Areas

“…Post-earthquake debris flows are characterized by their high destructive power, large scale, and the ease with which they form disaster chains (e.g., debris flows block river channels, causing river diversion and flooding of surrounding areas). Therefore, they seriously threaten human safety and endanger roads, bridges, houses, and other facilities Chen et al, 2015;Chen K.-T. et al, 2018;Chen et al, 2019a;Chen et al, 2019b;Xiong et al, 2020). Wenjia Gully, in Qingping Township, Mianzhu, Sichuan Province, China, was not a debris flow gully prior to the Wenchuan earthquake.…”