Scale effects in subaerial landslide generated impulse waves

Abstract

Hydraulic scale modelling involves scale effects. The limiting criteria for scale models of subaerial landslide generated impulse waves including solid, air, and water are discussed both based on a literature review and based on detailed two-dimensional experimentation. Seven scale series based on the Froude similitude were conducted involving the intermediate-water wave spectrum. Scale effects were primarily attributed to the impact crater formation, the air entrainment and detrainment, and the turbulent boundary layer as a function of surface tension and fluid viscosity. These effects reduce the relative wave amplitude and the wave attenuation as compared with reference experiments. Wave amplitude attenuation was found to be more than 70 times larger than predicted with the standard wave theory. Limitations for plane impulse wave generation on the basis of the present research are given by which scale effects can be avoided.

Composite modelling of subaerial landslide–tsunamis in different water body geometries and novel insight into slide and wave kinematics

“…To obtain the underlying empirical equations, the slide characteristics have been systematically varied in a number of subaerial landslide studies. This includes a substantial body of research conducted in wave channels (2D) (Noda, 1970;Wiegel et al, 1970;Kamphuis and Bowering, 1972;Slingerland and Voight, 1979;Huber and Hager, 1997;Monaghan et al, 2003;Walder et al, 2003;Fritz et al, 2004;Quecedo et al, 2004;Liu et al, 2005;Lynett and Liu, 2005;Zweifel et al, 2006;Ataie-Ashtiani and Nik-Khah, 2008;Heller et al, 2008;Abadie et al, 2010;Heller and Hager, 2010Fuchs et al, 2013;Heller andSpinneken, 2013, 2015) with fewer studies undertaken in wave basins (3D) (Huber and Hager, 1997;Panizzo et al, 2005;Mohammed and Fritz, 2012;Heller and Spinneken, 2015). All of the above studies are based on idealisations including a horizontal bottom, a fully-granular or fully-rigid slide, as well as wave generation and propagation in either 2D or 3D.…”

“…The geometry and bathymetry can be reproduced in great detail such that accurate results may be expected for a given slide scenario, provided that the model size is sufficiently large to rule out significant scale effects (Heller et al, 2008) and an appropriate slide model is selected. Disadvantages of method (iii) are that significant resources (laboratory space, measurement equipment) are required and that a typical time frame for an investigation exceeds one year.…”

“…The origin of the coordinate along the hill slope x' is placed at the same location. The most crucial unknown wave parameters are the wave amplitude a, the wave height H and the wave period T. Table 1 includes also the relevant dimensionless parameters, which can be derived with a dimensional analysis, as demonstrated by Heller et al (2008). These include the slide Froude number F = V s /(gh) 1/2 ≈ 1.51 (scenario 1) and 1.17 (scenario 2) with gravitational acceleration g and relative slide thickness S = s/h = 0.50 and 0.25.…”

On the effect of the water body geometry on landslide–tsunamis: Physical insight from laboratory tests and 2D to 3D wave parameter transformation

“…The tests programme was designed to vary the dimensional parameters in wide ranges and to include all four wave types Stokes-, cnoidal-, solitary-and bore-like waves as described in Heller and Hager (2011) and similar wave type classifications (Noda, 1970;Fritz et al, 2004;Zweifel et al, 2006). The test programme included three slides ( wave amplitude due to the Reynolds and Weber numbers may be considered negligible (Heller et al, 2008). Each slide was released from 3 different release positions x', resulting in three slide impact velocities V s (Table 1).…”

“…This is reflected in the large number of generic studies investigating subaerial landslide-tsunamis in 2D such as Noda (1970), Wiegel et al (1970), Kamphuis and Bowering (1972), Slingerland and Voight (1979), Huber and Hager (1997), Monaghan et al (2003), Walder et al (2003), Fritz et al (2004), Quecedo et al (2004), Liu et al (2005), Lynett and Liu (2005), Panizzo et al (2005), Zweifel et al (2006), Ataie-Ashtiani and Nik-Khah (2008), Heller et al (2008), Saelevik et al (2009), Abadie et al (2010), Hager (2010, 2011), Fuchs et al (2013) and Heller and Spinneken (2013). The number of generic studies conducted in 3D is considerably smaller, with Huber and Hager (1997), Liu et al (2005), Panizzo et al (2005) and Mohammed and Fritz (2012) as main contributors.…”