Waves and Sediment Transport Due to Granular Landslides Impacting Reservoirs

Abstract

Granular landslides impacting reservoirs may generate large waves and cause active sediment transport, and an increased understanding of these processes is important for public safety and effective reservoir management. This study investigates the waves and sediment transport caused by landslides impacting reservoirs using a two‐dimensional coupled double‐layer‐averaged shallow water hydro‐sediment‐morphodynamic model. In contrast to existing models, which cannot fully account for sediment transport, the model makes a physical step forward. The model is benchmarked against laboratory experiments of landslide‐generated waves in both two and three dimensions. Based on extended numerical cases, the capability of the model is further demonstrated by comparisons with empirical relationships of waves in 2‐D. In addition, sediment transport is resolved in terms of the sediment concentration and bed deformation. The results show that the wave types and amplitudes in 2‐D are dictated by the sediment transport speed, which also governs the landslide‐to‐wave momentum transfer and the landslide efficiency, which is defined as the ratio of the horizontal runout distance to the vertical fall height. With increasing sediment transport speed, landslide‐generated waves in 2‐D vary gradually from smaller nonlinear oscillatory waves to larger waves with solitary‐like wave characteristics, including nonlinear transition waves, solitary waves, and dissipative transient bores. In contrast to the momentum transfer ratio, the landslide efficiency increases with the sediment transport speed and decreases with the reservoir water depth and the lateral spreading in 3‐D cases.

Grain‐energy release governs mobility of debris flow due to solid–liquid mass release

“…This is significant and particularly timely, noting the acceleration in glacier melt and increasing trend in extreme precipitation amount, intensity, and frequency (Donat et al ., 2013), which are likely to trigger more debris flows. The study also has broad implications for unravelling a spectrum of earth surface processes, including heavily sediment‐laden floods due to storms and glacier lake outbursts (Laronne and Reid, 1993; Xiao et al ., 2010; Grinsted et al ., 2017; Cook et al ., 2018; Hook, 2019), and subaqueous debris flows and turbidity currents in rivers, reservoirs, estuaries, and the ocean (Weirich, 1988; Wright and Friedrichs, 2006; Talling et al ., 2007; Armanini, 2013; Cao et al ., 2015b; Paull et al ., 2018; Stevenson et al ., 2018; Li et al ., 2019).…”

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

“…As far as continuum models are concerned, double layer-averaged models hold great promise for resolving barrier lake formation due to their ability to reflect the two-way coupling between landslide motions and water flows [40] and the sensible balance between their theoretical integrity and applicability [22]. Double layer-averaged models employ two sets of governing equations to describe the lower water-sediment mixture flow (landslide) layer and the upper clear-water flow layer.…”

“…First, existing double layer-averaged models [22,[41][42][43] are based on a single-phase flow premise, in which the water-sediment mixture in the lower flow layer are regarded as a single-phase flow. Therefore, the velocities of the sediment phases in the lower flow layer are assumed to be equal to the mixture velocity.…”

“…Second, existing double layer-averaged models [22,[41][42][43] are confined to single-sized sediment transport (i.e., the sediment size is kept at a single value, normally the median or mean sediment diameter, throughout the simulation). Clearly, the models that assume a single sediment size do not reflect the nature of landslides, which are typically characterized by broad grain size distributions.…”

“…However, these experiments have mainly focused on landslide-generated-waves, while sediment transport and morphological evolution are sparsely observed [22]. Consequently, they are not able to fully reveal the complicated mechanism underlying barrier lake formation.…”