Material erosion under a multiphase flow is a very complex process influenced by many parameters. Understanding physical mechanisms and establishing governing laws for predicting the erosion rate are ...of great importance to alleviate or even avoid erosion damage in engineering applications. In this paper, we perform a combined numerical and experimental study to understand how the evolution of material surface induced by erosion can inversely affect the multiphase flow characteristics and erosion mechanisms on the surface. A water–sand erosion test-rig system is used to obtain the surface profiles, erosion rates and surface patterns of stainless steel under a water–sand multiphase flow. A multiphase flow model and an erosion model are combined to obtain the flow profile, erosion rate and erosion pattern. To gain insights into the multiphase flow and erosion mechanism changes due to the surface evolution induced by the erosion process, we take the surface profiles obtained from our testing samples at different stages of experiments to create geometry models for our numerical simulations. The numerical results are in good agreement with experimental results for erosion rate and erosion pattern as well as erosion mechanism. Through systematic numerical simulations, we clearly reveal the detailed changes in multiphase flow characteristics and erosion mechanisms arising from the surface evolution. The present work shows that the erosion process is very sensitive to the change of the test sample surface resulting from the change in erosion mechanism, highlighting the need to include the surface evolution in erosion modeling.
•A combined numerical–experimental study was performed to studyerosion process.•Water–sand erosion test-rig was used to obtain surface profiles and erosion rates.•Sample geometry models in simulations were created from measurement profiles.•Flow characteristics and erosion mechanism changes due to the surface evolution.•It is necessary to include the surface evolution in the erosion numerical modeling.
Debris flows are common geological hazards in mountainous regions worldwide. The scale of debris flows can be significantly enhanced by basal erosion and bank collapse in the transportation process, ...resulting in an increase in casualties and property losses. However, the mechanisms of this growth are largely unclear. Here, we conduct a series of experiments to investigate the erosion of two different bed sediments (coarse‐grained and widely graded) by released flows with three different densities and two different volumes. The erosion mechanisms of bed sediments are revealed by comparing detailed sensor data for flow level, pore pressure and total normal stress. A flow nose develops on the coarse‐grained bed sediment, resulting in a high flow depth and low velocity, while a tabular flow develops on the widely graded bed sediment, leading to a low flow depth and high velocity. The mean erosion rates of the coarse‐grained bed sediment are generally higher than those of the widely graded bed sediment due to significant pore pressure developed in coarse‐grained bed sediment. The feedback effect of bed sediment on the erosion process strongly influences the flow depth and velocity, which in turn affects the mean erosion rate of bed sediment. The interaction between the overlying flow and sediment bed controls the erosion pattern: coarse‐grained bed sediment is eroded by a layer of mass movement whereas widely graded bed sediment is progressively scoured. The interaction between debris flow and bed sediment during erosion is principally attributed to pore‐pressure transmission.
Key Points
Flow depth and velocity over a coarse‐grained sediment (d50 = 2.4 mm) and a widely graded sediment (d50 = 0.9 mm) differed substantially
The coarse‐grained bed sediment was eroded by mass movement while the widely graded bed sediment was progressively scoured
The interaction between the overlying flow and sediment bed controlled the erosion pattern
Understanding processes governing coastal erosion is becoming increasingly urgent because highly valued ecosystems like salt marshes are being lost at accelerating rates. Here we examine the role of ...biotic interactions in mediating marsh shoreline erosion under wind wave forces. We parameterized analytical and cellular automata models with field data to assess how soil heterogeneity among clonal patches of an ecosystem engineer mediates spatiotemporal patterns of marsh shoreline erosion. We found that spatial heterogeneity accelerates erosion, especially when it is organized in patches of intermediate size. Patch size also mediated interannual variability in erosion and strongly controlled shoreline roughness. Our results indicate that shoreline roughness can be diagnostic of internal biological structure and spatiotemporal variability in erosion. Hence, measures of shoreline roughness may inform the timeframe and spatial extent needed to accurately monitor erosion. These findings highlight how the physical response of marsh shorelines to wind wave erosion is a function of landscape ecology.
Plain Language Summary
Understanding processes governing coastal erosion is becoming increasingly urgent as highly valued ecosystems like salt marshes are being lost at accelerating rates. This paper investigates how marsh shoreline erosion is affected by the spatial composition of clonal plants. Plant “engineer” species are known to increase soil shear strength, decreasing rates of erosion. Consequently, phenotypic variation among clonal individuals may affect shoreline erosion. Because erosion proceeds as an advancing front, it may be influenced by how soil resistance is spatially organized. We found that, while random variation increased erosion rates, the effect was stronger when variation was organized into clonal patches—particularly ones that were intermediately sized. With increasing clone size, shoreline shape became rougher, and the variability of annual erosion rates increased. Not only does this highlight how a physical process is shaped by biotic attributes, it also shows how the resulting shoreline shape may be diagnostic of biological structure and influence.
Key Points
Analytical and simulation models show the role of biogeomorphic heterogeneity in mediating marsh shoreline erosion under wind wave forces
Acceleration of marsh erosion is greatest when soil spatial heterogeneity is organized by clonal vegetation patches of intermediate size
The variability of annual erosion rates and roughness of marsh shorelines increase with the size of clonal vegetation patches
Soil erosion is a major global soil degradation threat to land, freshwater, and oceans. Wind and water are the major drivers, with water erosion over land being the focus of this work; excluding ...gullying and river bank erosion. Improving knowledge of the probable future rates of soil erosion, accelerated by human activity, is important both for policy makers engaged in land use decision-making and for earth-system modelers seeking to reduce uncertainty on global predictions. Here we predict future rates of erosion by modeling change in potential global soil erosion by water using three alternative (2.6, 4.5, and 8.5) Shared Socioeconomic Pathway and Representative Concentration Pathway (SSP-RCP) scenarios. Global predictions rely on a high spatial resolution Revised Universal Soil Loss Equation (RUSLE)-based semiempirical modeling approach (GloSEM). The baseline model (2015) predicts global potential soil erosion rates of
43
−
7
+
9.2
Pg yr−1, with current conservation agriculture (CA) practices estimated to reduce this by ∼5%. Our future scenarios suggest that socioeconomic developments impacting land use will either decrease (SSP1-RCP2.6–10%) or increase (SSP2-RCP4.5 +2%, SSP5-RCP8.5 +10%) water erosion by 2070. Climate projections, for all global dynamics scenarios, indicate a trend, moving toward a more vigorous hydrological cycle, which could increase global water erosion (+30 to +66%). Accepting some degrees of uncertainty, our findings provide insights into how possible future socioeconomic development will affect soil erosion by water using a globally consistent approach. This preliminary evidence seeks to inform efforts such as those of the United Nations to assess global soil erosion and inform decision makers developing national strategies for soil conservation.
Margin lateral erosion is arguably the main mechanism leading to marsh loss in estuaries and lagoons worldwide. Our understanding of the mechanisms controlling marsh edge erosion is currently quite ...limited and current predictive models rely on empirical laws with limited general applicability. We propose here a simple theoretical treatment of the problem based on dimensional analysis. The identification of the variables controlling the problem and the application of Buckingham's theorem show, purely on dimensional grounds, that the rate of edge erosion and the incident wave power density are linearly related. The predictive ability of the derived relationship is then evaluated, positively, using new long‐term observations from the Venice lagoon (Italy) and by re‐interpreting data available in previous literature.
Key Points
Marsh edge erosion rate is a linear function of wave power density
Marsh edge erosion rate is a function of marsh cliff height
Traditional, power‐law, formulas are inconsistent with theory and observations
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