Analysis of River Blocking Induced by a Debris Flow

Abstract

many coseismic landslides along the Nanya River in Shimian City. Subsequent debris flows that initiated from these landslides and are triggered by intense rainfall become the secondary hazard in the years after the earthquake; in particular, some debris flows led to a serious river blocking event. For example, the Guangyuanbao debris flow which occurred on July 04, 2013, partly blocked the Nanya River, presenting a major threat to the national highway and residential areas. To analyze the pattern of landslide damming, we analyzed numerical simulations of the movement characteristics of the Guangyuanbao debris flow using rainfall intensities with varying recurrence periods of 5, 20, and 50 years. The accuracy of the spreading of the numerical simulation is about 90%. The simulation indicated a small volume of sediment entering the river for a rainfall under 5-year return period. A debris flow induced by rainfall under 20-year return period partly blocked the river, while rainfall under 50-year return period has potential to block the river completely. This proposed analysis of river blocking induced by a debris flow could be used for disaster prevention in earthquake-stricken area.

Review of Investigations on Hazard Chains Triggered by River-Blocking Debris Flows and Dam-Break Floods

“…Liu and Zhou (2015) D 21.18 When the head of the debris flows reaches the opposite bank and a large volume continues to flow into the river, the main river can be completely blocked; thus, a dam is formed (Wang et al, 2017).…”

“…The internal composition of debris flows and the dynamic process of river blockage are complex. There are great differences between the dams induced by debris flows and the ones induced by the landslides (or maimora dam) (Wang et al, 2017;Wu et al, 2020). The former is difficult to maintain long-term stability and often bursts soon, and dam failure often occurs when there is an overtopping flow (Yan et al, 2009).…”

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

“…Stream. The formation of a landslide dam caused by a tributary debris flow occurs when two conditions are met: (1) the run-out distance of the tributary debris flow is greater than the width of the main stream, and (2) the minimum deposition thickness of the tributary debris flow is higher than the in situ water depth of the main stream [6,[11][12][13][14]. If the above two processes have not occurred simultaneously, we define any alteration to the course of the impacted river as a river change phenomenon.…”

“…However, two important issues were not considered in these studies, namely, (1) whether the tributary debris flow can reach the far bank of the main stream and (2) whether the minimum deposition thickness of the tributary debris flow is higher than the water depth of the main stream. Recently, consideration of the run-out distance of a tributary debris flow and its minimum deposition thickness was evaluated to establish a more accurate assessment method of landslide dam formation caused by tributary debris flows [6,[11][12][13][14]. Although the results of these studies satisfy the formation conditions of a dam, additional characteristics, such as the hydraulic interaction between the arriving debris flow and the receiving main river, which causes additional resistances to debris-flow propagation, have not been considered.…”

An Experimental Study on the Hydromechanical Behaviours of the Evolution of Postearthquake Landslide Deposits

“…In such a condition, shallow headward failures have occurred on both sides of the extensional rills and gullies in these landslide deposits. Mass remobilization provided a considerable amount of source materials for the initiation of debris flows, thereby directly causing postseismic debris flow outbreaks in the earthquake-stricken area [9][10][11] and seriously threatening local reconstruction and safety. Investigations of abrupt topographic transformations, rapid erosional processes, and changes in material source conditions have become new priorities for prevention and management of postseismic debris flow.…”