An official website of the United States government
ABSTRACT Backward erosion piping (BEP) is a leading internal erosion mechanism for flood protection system failures. A model capable of predicting critical hydraulic conditions for BEP initiation at multiple scales while also incorporating soil variability is a pressing need. This study formulates and validates a novel multiscale probabilistic BEP initiation framework with incorporation of soil variability. The framework is based on a grain‐scale probabilistic model and the weakest link theory, and the theory of rate processes. The multiscale framework proposed herein is validated through a wide range of available experimental data from independent sources, encompassing tests performed at multiple scales. Following calibration with small‐scale experimental data, the model demonstrates accurate prediction of critical hydraulic gradients at larger scales (3–6 orders of magnitude difference), including the ability to capture the grain size dependence of BEP initiation and providing uncertainty estimates. A systematic analysis is performed to uncover the effects of different soil properties on multiscale critical hydraulic conditions.
more »
« less
A Unified Phenomenological Model Captures Water Equilibrium and Kinetic Processes in Soil
Abstract Soil water sustains life on Earth, and how to quantify water equilibrium and kinetics in soil remains a challenge for over a century despite significant efforts. For example, various models were proposed to interpret non‐Darcian flow in saturated soils, but none of them can capture the full range of non‐Darcian flow. To unify the different models into one overall framework and improve them if needed, this technical note proposes a theory based on the tempered stable density (TSD) assumption for the soil‐hydraulic property distribution, recognizing that the underlying hydrologic processes all occur in the same, albeit very complex and not measurable at all the relevant scales, soil‐water system. The TSD assumption forms a unified fractional‐derivative equation (FDE) using subordination. Preliminary applications show that simplified FDEs, with proposed hydrological interpretations and TSD distributed properties, effectively capture core equilibrium and kinetic water processes, spanning non‐Darcian flow, water retention, moisture movement, infiltration, and wetting/drying, in the soil‐water system with various degrees and scales of system heterogeneity. Model comparisons and evaluations suggest that the TSD may serve as a unified density for the properties of a broad range of soil‐water systems, driving multi‐rate mass, momentum, and energy equilibrium/kinetic processes often oversimplified by classical models as single‐rate processes.
more »
« less
- Award ID(s):
- 2305141
- PAR ID:
- 10495915
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 60
- Issue:
- 3
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
It has been established that Newton’s law of viscosity fails for fluids under strong confinement as the strain-rate varies significantly over molecular length-scales. We thereby investigate if a nonlocal shear stress accounting for the strain-rate of an adjoining region by a convolution relation with a nonlocal viscosity kernel can be employed to predict the gravity-driven isothermal flow of a Weeks–Chandler–Andersen fluid in a nanochannel. We estimate, using the local average density model, the fluid’s viscosity kernel from isotropic bulk systems of corresponding state points by the sinusoidal transverse force method. A continuum model is proposed to solve the nonlocal hydrodynamics whose solutions capture the key features and agree qualitatively with the results of non-equilibrium molecular dynamics simulations, with deviations observed mostly near the fluid–channel interface.more » « less
-
A widely used approach to modeling discrete‐time network data assumes that discrete‐time network data are generated by an unobserved continuous‐time Markov process. While such models can capture a wide range of network phenomena and are popular in social network analysis, the models are based on the homogeneity assumption that all nodes share the same parameters. We remove the homogeneity assumption by allowing nodes to belong to unobserved subsets of nodes, called blocks, and assuming that nodes in the same block have the same parameters, whereas nodes in distinct blocks have distinct parameters. The resulting models capture unobserved heterogeneity across nodes and admit model‐based clustering of nodes based on network properties chosen by researchers. We develop Bayesian data‐augmentation methods and apply them to discrete‐time observations of an ownership network of non‐financial companies in Slovenia in its critical transition from a socialist economy to a market economy. We detect a small subset of shadow‐financial companies that outpaces others in terms of the rate of change and the desire to accumulate stocks of other companies.more » « less
-
Abstract Several new methods are proposed that can diagnose the interscale transfer (or spectral flux) of kinetic energy (KE) and other properties in oceanic and broader geophysical systems, using integrals of advective structure functions and Bessel functions (herein “Bessel methods”). The utility of the Bessel methods is evaluated using simulations of anisotropic flow within two-dimensional (2D), surface quasigeostrophic (SQG), and two-layer QG systems. The Bessel methods diagnose various spectral fluxes within all of these systems, even under strong anisotropy and complex dynamics (e.g., multiple cascaded variables, coincident and opposing spectral fluxes, and nonstationary systems). In 2D turbulence, the Bessel methods capture the inverse KE cascade at large scales and the downscale enstrophy cascade (and associated downscale energy flux) at small scales. In SQG turbulence, the Bessel methods capture the downscale buoyancy variance cascade and the coincident upscale wavenumber-dependent KE flux. In QG turbulence, the Bessel methods capture the upscale kinetic energy flux. It is shown that these Bessel methods can be applied to data with limited extent or resolution, provided the scales of interest are captured by the range of separation distances. The Bessel methods are shown to have several advantages over other flux-estimation methods, including the ability to diagnose downscale energy cascades and to identify sharp transition scales. Analogous Bessel methods are also discussed for third-order structure functions, along with some caveats due to boundary terms. Significance StatementBig ocean eddies play an important role in Earth’s energy cycle by moving energy to both larger and smaller scales, but it is difficult to measure these “eddy energy fluxes” from oceanic observations. We develop a new method to estimate eddy energy fluxes that utilizes spatial differences between pairs of points and can be applied to various ocean data. This new method accurately diagnoses key eddy energy flux properties, as we demonstrate using idealized numerical simulations of various large-scale ocean systems.more » « less
-
Soil piping (concentrated leak erosion) is a major contributor to soil erosion in many parts of the world, and collapse of eroded pipes can result in the formation of gullies and sinkholes or trigger slope instability. Despite these significant impacts, there is little understanding of factors controlling pipe collapse, and how water within the pipe influences moisture levels within a slope. In this study, physical models were employed on unsaturated model slopes with pre-formed macropores to investigate how soil properties, pipe characteristics, and hydraulic conditions govern internal erosion processes and slope stability. Experiments simulated shallow field conditions (0.45 m overburden) using 4 mm and 12 mm pipes to establish preferential flow paths, while varying model parameters including initial compaction moisture content and density, pipe condition (absent, closed, or open), slope angle, and model width. Volumetric water content sensors monitored moisture evolution, while cameras captured slope responses to subsurface flow. Results demonstrate that initial compaction conditions (water content and density), pipe size, hydraulic connectivity, and pipe condition control internal erosion processes and slope stability.more » « less
