Threshold phenomena in erosion driven by subsurface flow

Lobkovsky, Alexander E.; Jensen, Bill; Kudrolli, Arshad; Rothman, Daniel H.

doi:10.1029/2004jf000172

Cited by 94 publications

(55 citation statements)

References 29 publications

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“…where f ϭfluid density; gϭgravitational acceleration; dϭgrain Lobkovsky et al 2004͒. This research extends such seepage erosion experiments for simulating natural streambank profiles with much larger slopes and investigated the combined erosion of seepage and bank failure.…”

Section: Introductionmentioning

confidence: 99%

“…Accumulated sediment from subsurface induced streambank failure must be removed for continued subsurface flow erosion. Research has begun to investigate the interaction of surface erosion, fluidization, and slumping whereby the onset of erosion is controlled not only by surficial flows but also hydrodynamic stress from groundwater seepage ͑Lobkovsky et al 2004;Worman 1993͒. Indoor flume studies indicate that surface erosion rates increase by an order of magnitude when unsaturated pore-water pressures increase to near saturation, thereby decreasing the soil shear strength ͑Rockwell 2002; Owoputi and Stolte 2001͒.…”

Section: Introductionmentioning

confidence: 99%

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Sediment Transport Model for Seepage Erosion of Streambank Sediment

et al. 2006

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Erosion by lateral, subsurface flow is known to erode streambank sediment in numerous geographical locations; however, the role of seepage erosion on mass failure of streambanks is not well understood. In the absence of an established sediment transport model for seepage erosion, the objectives of this research were to investigate the mechanisms of erosion due to concentrated, lateral subsurface flow and develop an empirical sediment transport model for seepage erosion of noncohesive sediment on near-vertical streambanks. Laboratory experiments were performed using a two-dimensional soil lysimeter of a reconstructed streambank profile packed with three different soil layers to mimic seepage erosion occurring at Little Topashaw Creek ͑LTC͒ in northern Mississippi. Soil samples from LTC streambanks indicated considerable hydraulic conductivity contrast between an overlying silt loam layer ͑SiL͒, highly permeable loamy sand, and confining clay loam layer. Lysimeter experiments were conducted with various upstream water table heads, overburden heights, and lysimeter slopes. Bank failure occurred prior to the total release of negative pore-water pressures in the SiL layer suggesting that such a mechanism was not critical for bank collapse due to seepage erosion. A seepage erosion transport model for conductive, noncohesive soil layers was derived based on a dimensionless sediment discharge and dimensionless seepage flow shear stress. The advantage of this sediment transport model is that it relates sediment flux to seepage discharge from the streambank.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sediment Transport Model for Seepage Erosion of Streambank Sediment

et al. 2006

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“…These types of failures are often referred to as pop out or tension failures. Lobkovsky et al (2004) showed that seepage force is proportional to the hydraulic gradient with the following relationship:…”

Section: Introductionmentioning

confidence: 99%

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

et al. 2013

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The effects of seepage on streambank erosion and failure are less understood compared to fluvial processes, especially the linkage between surface water and groundwater mechanisms. Field data are needed to validate laboratory seepage erosion and instability conclusions and to understand how engineering tools and methods may be applied to field conditions. An innovative trench injection system was utilized to provide a constant head on a near-streambank groundwater system when filled with stream water. This research was performed on a streambank of Dry Creek, a deeply incised stream with near-vertical banks located in Mississippi. Experiments included installing a trench (2.8 m from the bank and 2 m below ground surface) and a network of tensiometers and observation wells to measure soil-water pressures and water table elevations. Bank stratigraphy consisted of a sloping, conductive loamy sand layer between cohesive streambank layers. Groundwater conditions were monitored during a series of induced-seepage experiments. The bank face was outfitted with a seepage collection device to measure seep flow rates and sediment concentrations. Seepage flow rates (as high as 0.4 L=min) and corresponding erosion rates (as high as 0.86 kg=min) were proportional to estimated hydraulic gradients in the near-streambank region and followed an excess flow rate equation. However, flow paths and hydraulic gradients were largely nonuniform due to local variability in streambank stratigraphy, suggesting difficulty when attempting to apply engineering analyses of bank erosion and stability for seepage processes without accounting for this heterogeneity. Seepage flow and erosion became restricted when small-scale bank failures due to undercutting blocked flow pathways and limited particle mobilization, termed temporary self-healing. Seepage erosion was shown to be an important mechanism of streambank failure, especially when acting in concert with fluvial erosion processes that prevent permanent self-healing of seeps.

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“…When seepage occurs, seepage gradient forces (SF) exert body forces on streambank sediment proportional to the hydraulic gradient (Lobkovsky et al, 2004;Chu-Agor et al, 2009):…”

Section: Introductionmentioning

confidence: 99%

Numerically predicting seepage gradient forces and erosion: Sensitivity to soil hydraulic properties

Fox

Heeren

Wilson

et al. 2010

Journal of Hydrology

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s u m m a r yResearch has suggested that streambank seepage can be an important mechanism of bank instability; however, limited information is available on the level of soil characterization necessary to accurately predict seepage gradient forces and erosion. The objective of this research was to quantify the expected range of predicted seepage gradients for various degrees of site characterization. Uncertainty analysis on seepage gradient predictions was performed relative to variability in soil hydraulic properties. A two-dimensional unsaturated/saturated groundwater flow model was used to simulate a homogeneous soil layer for sand and loamy sand soils packed at various bulk densities, q b . A pedotransfer function (ROSETTA), designed to estimate unsaturated hydraulic properties from surrogate soil data (i.e., texture and bulk density), was used to derive the saturated hydraulic conductivity, K s , and water retention parameters for various levels of site information (i.e., only textural class; percent sand, silt, and clay (%SSC); %SSC and q b ; and %SSC, q b , and K s ). Statistical distributions were derived for each soil hydraulic parameter and Monte Carlo simulations were performed to generate distributions of maximum seepage gradient. The deviation in predicted seepage gradient was calculated using assumed baseline conditions. Ranges in predicted soil hydraulic parameters and maximum seepage gradients were considerably reduced when using %SSC as compared to soil texture. Therefore, at a minimum, soil samples should be taken for particle size analysis. For q b between 1450 and 1500 kg m À3, soil hydraulic parameters could be derived using ROSETTA and inputting %SSC, with little additional benefit provided by measuring q b and/or K s . When the q b was less than 1450-1500 kg m À3, inputting q b and/or K s consistently reduced the magnitude of deviations from the baseline and therefore should be measured from undisturbed soil samples. The opposite was observed for q b greater than 1450-1500 kg m À3 due to discrepancies between ROSETTA-derived and actual values of soil hydraulic parameters other than K s . Considerable deviations (i.e., around 20%) were observed in seepage gradients under this scenario. When ROSETTA-derived and actual values of soil hydraulic parameters more closely matched, inputting q b and/or K s benefitted seepage gradient predictions as deviations in seepage gradients were less than 5% for the sand and loamy sand soils. Therefore, it is vital to quantify all soil hydraulic parameters for high q b soils and textures with a wide range in %SSC.

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Threshold phenomena in erosion driven by subsurface flow

Cited by 94 publications

References 29 publications

Sediment Transport Model for Seepage Erosion of Streambank Sediment

Sediment Transport Model for Seepage Erosion of Streambank Sediment

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

Numerically predicting seepage gradient forces and erosion: Sensitivity to soil hydraulic properties

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