Mechanism of Tsunami-Induced Erosion of Bridge-Abutment Backfill and Its Countermeasures

Tsunamis can destroy bridges in coastal areas. Studies have attempted to unravel the mechanism of tsunami-induced damage and develop effective countermeasures against future tsunamis. However, the mechanisms of tsunami-induced erosion of bridge-abutment backfill and its countermeasures have not been studied adequately. This study investigates this topic using numerical analysis. The results show that the tsunami flowing down along the downstream wing of the abutment induces bedload sediment transport on the ogive section of the backfill on the downstream side of the abutment, resulting in the onset of backfill erosion. Sediment suspension and bedload sediment transportation occur when the backfill inside the abutment starts to flow out from below the downstream wing. This leads to subsidence of the backfill at the upstream side of the downstream wing. The subsequent backfill erosion is mainly caused by bedload sediment transport. Numerical experiments on countermeasures show that extending the wings downward can prevent the acceleration of backfill erosion in the presence of the abutment. A combination of multiple countermeasures, including extended wings, would be more effective in maintaining the stability of the abutment after a tsunami. This suggests the application of such countermeasures to actual bridges as an effective countermeasure against backfill erosion.

Analysis of Changes in Land Use/Land Cover and Hydrological Processes Caused by Earthquakes in the Atsuma River Basin in Japan

The 2018 Hokkaido Eastern Iburi earthquake and its landslides threaten the safety and stability of the Atsuma River basin. This study investigates land use and land cover (LULC) change by analyzing the 2015 and 2020 LULC maps of the basin, and its impact on runoff and sediment transport in the basin by using the soil and water assessment tool (SWAT) model to accurately simulate the runoff and sediment transport process. This study finds that the earthquake and landslide transformed nearly 10% of the forest into bare land in the basin. The simulation results showed that the runoff, which was simulated based on the 2020 LULC data, was slightly higher than that based on the 2015 LULC data, and the sediment transport after the earthquake is significantly higher than before. The rate of sediment transportation after the earthquake, adjusted according to the runoff, was about 3.42 times more than before. This shows that as the forest land decreased, the bare land increased. Conversely, the runoff increased slightly, whereas the sediment transport rate increased significantly in the Atsuma River basin after the earthquake. In future, active governance activities performed by humans can reduce the amount of sediment transport in the basin.

Estimating rill erosion and sediment transport processes along a saturated purple soil slope

A plough pan with reduced permeability always accumulates infiltrated water along slopes then saturates the cultivated layer under continuous rain. Topsoil saturation is a frequent phenomenon and an important process of the special soil slopes. A methodology and device system was used in this study to keep cultivated purple soil saturated. Strands of scouring tests were developed to quantify the rill erosion and sediment transport processes along a saturated purple soil slope at four experiment slopes (5°, 10°, 15°, and 20°) and three flow discharges (2, 4 and 8 L min−1). The experimental results indicated that the sediment transport capacity on a saturated purple soil slope ranged from 0.03 to 1.56 kg s−1 m−1 with the increasing trend along the slope gradient and flow discharge, and the increasing trend could be well matched by a nonlinear multivariable equation. The sediment concentration of the saturated purple soil slope exponentially increased with rill length and decreased with the increment rate and the maximum sediment concentrations observed in this study in different hydraulic events ranged from 108.13 to 1174.20 kg m-3. Saturated and non-saturated purple soil slopes erode differently with the maximum sediment concentration of saturated purple soil slope recorded at approximately 1.42-2.10 times the values for non-saturated purple soil slope. The findings of this research help illustrate the sediment transportation and erosion behaviors of a saturated purple soil slope, and serve as the basis for determining the parameters in the erosion models of the purple soil slope.

Surface processes control on orogenic evolution: inferences from 3D coupled numerical models and observations from the India-Eurasia collision zone

<p>The inherent links between tectonics, surface processes and climatic variations have long since been recognised as the main drivers for the evolution of orogens. Oceanic and continental subduction and collision processes lead to distinct topographic signals. Simultaneously, different climatic forcing factors and denudation rates substantially modify the style of deformation leading to different stress and thermal fields, strain localisation and even deep mantle evolution. An ideal area where the above-mentioned processes and their connections can be studied is the India-Eurasia collision zone.</p><p>Understanding the complex interplay between tectonics, erosion, sediment transportation and deposition requires the coupled application of thermo-mechanical and surface processes modelling techniques. To this aim, we used a 3D coupled numerical modelling approach. The influence of different plate convergence, erosion and sedimentation rates has been tested by the thermo-mechanical code I3ELVIS (Gerya and Yuen, 2007) coupled to the diffusion-advection based (FDSPM) surface processes model.</p><p>We show preliminary results to demonstrate  that the diffusion-advection erosion implementation has significant effects on local and regional mass redistribution and topographic evolution within narrow, curved, high orogens such as the Himalayas and their syntaxes, where erosion is a dominant forcing factor. We also discuss possible implications from different erosion/sedimentation implementations such as DAC (Ueda et al., 2015; Goren et al., 2014) in combination with the reference thermo-mechanical model to analyse changes in orogenic development as a consequence of different erosional processes in more detail.</p><p>References:</p><p>Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1-4), 83-105. <br>Ueda, K., Willett, S. D., Gerya, T., & Ruh, J. (2015). Geomorphological–thermo-mechanical modeling: Application to orogenic wedge dynamics. Tectonophysics, 659, 12-30.<br>Goren, L., Willett, S. D., Herman, F., & Braun, J. (2014). Coupled numerical–analytical approach to landscape evolution modeling. Earth Surface Processes and Landforms, 39(4), 522-545.</p>

Typical debris-flow barrier dams and associated outburst floods in the southeastern Tibet

<p>Large-magnitude debris flows up to a volume of 1.0 million m3 happen frequently in the southeastern margin of Tibetan plateau due to rapid rock uplift, high relief and abundant rainfall. These flows with high bulk density can easily block main rivers. Such debris-flow barrier dams fail very quickly, resulting in outburst floods and intensive sed-iment transport. We collect data of four recent large-scale debris-flow damming events at Peilong, Yigong, Tianmo and Sedongpu catch-ments, and examine the process of riverbank erosion and sediment transportation under dam narrowing and outburst flooding. More than 10% of debris mass was delivered downstream when the dams breached. It is concluded that debris flow is main erosion way in this area, and the very high erosion rate play a key role on river morpholo-gy in southeast Tibet.</p>

Estimation of Water Erosion and the Sediment Transportation in the Upper Basin of Cuxtepeques River, Chiapas, Mexico

Changes in land use and increased intensity of rainfall are factors of greater influence that accelerate the soil erosion process. The application of basin scale sedimentological models integrated to Geographic Information Systems (GIS), is a tool that allows the definition of critical zones, and of this the establishment of measures of control of processes of production and transport of sediments. This study evaluates the water erosion using the Universal Soil Loss Equation (USLE), five scenarios were studied: corresponding to the start of operations of the El Portillo II (1980) dam, and the before and after the two extreme events in the basin (September 1998 and October 2005). The transport of sediments was evaluated by regression, using full annually records (eight years) of flows of two gauging stations in the basin. Overall, variations in erosion rates were observed with changes in the vegetal coverage and statistical homogeneity in the gauging data, which allowed adjust them to a regression model, with correlation coefficient upper to 88%.

Sedimentology, depositional environment and classification of Karkheh River’s Delta, West of Khuzestan Plain (SW of Iran)

Karkheh river’s Delta is located in the west of Khuzestan Plain and can be divided into two smaller deltas; northern delta named as Karkheh Delta (including Bostan, Sableh and Neisan Deltas) and southern delta named as Karkheh -e- Noor Delta. Based on Galloway7 classification, Karkheh Delta is river-dominated type (type 1). Considering activity, this delta is divided to two parts; an active part in north and an inactive part in south. Based on Orton and Reading 16 classification, Karkheh Delta is placed in fine-grained (muddy) delta category due to prevailing silt and clay. In terms of sediment transportation and deposition process, this delta is a constructive delta. To recognize changes of Karkheh Delta’s area, Landsat images 5, 7 and 8 were studied and compared using 13 satellite images from 1973 to 2016 which shows an increase in the delta’s area particularly in northern part. In order to study sedimentology of this delta, 25 samples were taken. Sediment sizing analysis results show that silt is the most abundant sediment on average in this delta whereas clay, sand and gravel are in next abundance. Due to Shepard 17 classification, in Karkheh delta, silty clay, clay silt, silt, sandy silt and clay-silt-sand were identified. Also, channel, flood plain, crevasse, levee and sabkha depositional environments could be recognized in this delta.

Improved Coastal Erosion Prevention Using a Hybrid Method with an Artificial Coral Reef: Large-Scale 3D Hydraulic Experiment

Coastal erosion, a worldwide social issue, has garnered substantial attention. Numerous methods have been implemented to control coastal erosion problems; however, the presence of rigid structures limits erosion mitigation, thereby causing various challenges. For instance, in the case of submerged breakwaters, local scour in front of the structure and scour caused by the flow occurring in open inlets affect the subsidence and stability of the structure and can also cause structural failure. To solve these problems, this paper proposes a hybrid method of using a submerged breakwater with an artificial coral reef installation; further, this study evaluates the attenuation of waves and mitigation of sediment transportation through large-scale 3D hydraulic experiments. We found that the hybrid method with an artificial coral reef installed in the open inlet shows excellent wave control and plays a clearly beneficial role in the advancement of the shoreline. The artificial coral reef method reduced the return flow generated by the drag force at the breakwater shoulder and open inlet. In addition, scour at the breakwater shoulder was inhibited by collecting the sand escaping offshore. Simultaneously, scour at the open inlet was also mitigated. The application of the hybrid method compensated for the problems caused by local scour and erosion in the submerged breakwater, thereby leading to the improvement of its function. Therefore, the hybrid method proposed in this paper was determined to be applicable not only for submerged breakwaters, but also for various structures for controlling coastal erosion.