Progress 06/01/06 to 08/31/09
Outputs
OUTPUTS: This research has demonstrated the importance of seepage erosion processes in leading to streambank erosion and failure and sediment loading to streams. Hydrologic, soil and geotechnical characteristics and processes for seepage gradient forces and erosion undercutting have been quantified at two stream sites in Mississippi. Two-dimensional lysimeter experiments of repacked banks exposed to seepage forces were performed and data collected under controlled laboratory settings. Using this data, the role of seepage erosion relative to other streambank failure processes has been investigated using numerical models. An investigation has also been completed on the importance of seepage undercutting relative to root reinforcement by vegetation using the USDA-ARS Bank Stability and Toe Erosion Model (BSTEM). Innovative three-dimensional soil block experiments, with and without vegetation and experiencing instability by seepage, have also been performed. Improved sediment transport functions were developed using data from the three-dimensional soil block experiments. Uncertainty analyses were performed using the seepage erosion sediment transport function relative to variability in soil hydraulic properties using Monte Carlo analysis. The uncertainty analyses were performed to determine which soil properties were most critical for identifying potential seepage locations and quantifying seepage flow rates. Routines for incorporating seepage gradient forces and seepage erosion undercutting into existing process-based models of streambank stability have been completed. Dissemination of research findings occurred through presentations at local, state, and national meetings and publication of peer-reviewed journal articles and conference proceedings during the project period. Nine peer-reviewed journal publications were published during the funding period with two more journal manuscripts currently in review. Two of these peer-reviewed publications have been selected by separate journals as representing unique, innovative research efforts. Twelve conference proceedings paper were published along with numerous other conference presentations and posters. The PI was an invited speaker on seepage erosion at two different conferences. Graduate student papers and presentations on this topic have received state (Oklahoma Water Resources Conference) and national recognition (2007 and 2009 National ASABE Graduate Student Paper Awards). This research supported one Master of Science student (graduated in 2008 and now working with a stream restoration consulting firm in Sacramento, CA) and one Ph.D. student (graduated in 2009 and now working as a post-doctoral research associate at the University of Florida). Funds also supported undergraduate education through undergraduate research assistantships. Materials derived from the research have been incorporated into undergraduate and graduate courses at Oklahoma State University. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Select erosive events in areas across the United States lead to high sediment loading in rivers and streams. This must be addressed through riparian management. However, the range of possible solutions remains limited until we better understand the surface water/ground water interactions. This research has significantly extended theory on the role of ground water in erosion and provided new tools for multidisciplinary researchers to determine the importance of seepage flow gradients and erosion undercutting for numerous soil, hydrologic, and environmental conditions. Seepage leads to streambank instability through three interrelated mechanisms: (1) increased soil pore-water pressure reducing the shear strength of the soil, (2) seepage gradient forces, and (3) seepage particle mobilization and undercutting. The soil bulk density controlled the seepage failure mechanism: (1) tension or pop-out failures due to the seepage force exceeding the soil shear strength which was being concurrently reduced by increased soil pore-water pressure, or (2) particle entrainment in the seepage flow, particle mobilization, bank undercutting, and bank collapse when the initial seepage force gradient was less than the resistance of the soil block. Seepage erosion undercutting can be as important as increased soil pore-water pressure in leading to bank failure. It becomes a prominent bank failure mechanism, even with undercutting distances as small as 20 cm on root-reinforced streambanks. Visible root structures on the streambank face can control seepage undercut shapes. A seepage erosion sediment transport function was developed from three-dimensional soil block experiments. This was represented by an excess gradient function wherein the rate of erosion was related to the difference between the flow gradient and a critical gradient. The former was estimated from Darcy's Law with an adjustment to take into account the distance of seepage undercutting. Mechanistically, the critical gradient should be a function of the soil cohesion, and in this research the critical gradient was related to the effective cohesion through a logarithmic relationship. The relationship between the eroded volume per bank face area and the maximum distance of seepage undercutting was also derived based on an assumed Gaussian function for the undercut shape. Uncertainty analyses suggested that using soil texture alone to derive soil hydraulic parameters for seepage erosion prediction was insufficient. Inputting percent sand, silt, and clay consistently reduced variability in soil hydraulic parameters and corresponding errors in predicted seepage erosion rates. It is vital to have a complete quantification of soil hydraulic parameters when predicting seepage for higher bulk density soils and/or textures with a wide range in percent sand, silt, and clay. Routines for the integration of seepage undercutting into a bank stability model has lead to the development of a dynamic riparian simulation tool which will link bank stability with the adjacent, riparian groundwater system, leading to a critical tool for stability analyses in river rehabilitation.
Publications
- Fox, G.A., Heeren, D.M., G.V. Wilson, E. Langendoen, A.K. Fox, and M.L. Chu-Agor. 2009. Numerically predicting seepage erosion: Sensitivity to soil hydraulic properties. In Review.
- Fox, G.A. and G.V. Wilson. 2009. The role of subsurface flow in hillslope and streambank erosion: Status and research needs. In Review.
- Lindow, N., and G.A. Fox. 2009. Seepage erosion in fluviomarine stream bank material. Earth Surface Processes and Landforms (In Press).
- Chu-Agor, M.L., G.A. Fox, and G.V. Wilson. 2009. Empirical sediment transport function predicting seepage erosion undercutting for cohesive bank failure prediction. Journal of Hydrology 377: 155-164.
- Agor, M.L., G.A. Fox, and G.V. Wilson. 2009. Incorporating Seepage Processes into a Streambank Stability Model. ASABE Annual International Conference, Reno, NV, June 21-25, 10 pages.
- Heeren, D.M., G. A. Fox, M. Chu-Agor, and G. V. Wilson. 2009. Predicting Streambank Seepage Flows: Sensitivity to Soil Properties and Layering.
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Progress 06/01/07 to 05/31/08
Outputs
OUTPUTS: This research has demonstrated the importance of seepage erosion processes in leading to streambank erosion and failure and sediment loading to streams. Recent progress has demonstrated that seepage leads to streambank instability through three interrelated mechanisms: (1) increased soil pore-water pressure reducing the shear strength of the soil, (2) seepage gradient forces, and (3) seepage particle mobilization and undercutting (Chu-Agor et al., 2008, Journal of Hydrology and Journal of Hydrologic Engineering). Hydrologic, soil, and geotechnical characteristics and processes for seepage gradient forces and erosion undercutting have been quantified at an additional stream site in Mississippi (Fox et al., 2007, Earth Surface Processes and Landforms). Using two-dimensional lysimeter experiments of repacked banks exposed to seepage forces, a modified empirical sediment transport function was proposed and evaluated for seepage erosion (Fox et al., 2007, Soil Science Society of America Journal). Using data from previous lysimeter experiments, the role of seepage erosion relative to other streambank failure processes has been investigated. Seepage erosion undercutting can be as important as increased soil pore-water pressure in leading to bank failure (Chu-Agor et al., 2008, Journal of Hydrologic Engineering; Fox et al., 2007, Earth Surface Processes and Landforms). An investigation has also been completed on the importance of seepage undercutting relative to root reinforcement by vegetation using the USDA-ARS Bank Stability and Toe Erosion Model (BSTEM). This research demonstrated that seepage undercutting becomes a prominent bank failure mechanism, even with undercutting distances as small as 20 cm on root-reinforced streambanks (Cancienne et al., 2008, Earth Surface Processes and Landforms). Innovative three-dimensional soil block experiments, with and without vegetation and experiencing instability by seepage, have also been performed (Chu-Agor et al., 2008, Journal of Hydrology). The soil bulk density, which affected the soil's cohesion, controlled the seepage failure mechanism: (1) tension or "pop-out" failures due to the seepage force exceeding the soil shear strength which was being concurrently reduced by increased soil pore-water pressure, or (2) particle entrainment in the seepage flow, particle mobilization, bank undercutting, and bank collapse when the initial seepage force gradient was less than the resistance of the soil block. In the vegetated soil blocks, visible root structures on the bank face controlled the undercut shapes. Currently, research is underway to modify an existing process-based model of stream stability (BSTEM) to include seepage gradient forces and seepage erosion undercutting. Improved sediment transport functions are also under development using data from the three-dimensional soil block experiments along with routines for incorporating seepage erosion undercutting into bank stability models. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Select erosive events in many areas across the United States lead to high sediment loading in rivers and streams. This sediment loading must be addressed through riparian management. However, the range of possible solutions remains limited until we better understand the surface water/ground water interactions. This research has significantly extended theory on the role of ground water in erosion and provided new tools for multidisciplinary researchers to determine the importance of seepage erosion and undercutting for numerous soil, hydrologic, and environmental conditions. The initial integration of seepage undercutting into a bank stability model has provided guidance for developing a dynamic riparian simulation tool which will link bank stability with the adjacent, riparian groundwater system, leading to a critical tool for stability analyses in river rehabilitation.
Publications
- Agor, M.L., G.A. Fox, and G.V. Wilson. 2008. A seepage erosion sediment transport function and geometric headcut relationships for predicting seepage erosion undercutting. In Review.
- Chu-Agor, M., G.V. Wilson, and G.A. Fox. 2008. Numerical modeling of bank instability by seepage erosion undercutting of layered streambanks. Journal of Hydrologic Engineering 13(12): In Press (December 2008).
- Cancienne, R., G.A. Fox, and A. Simon. 2008. Influence of seepage undercutting on the root reinforcement of streambanks. Earth Surface Processes and Landforms 33(11): 1769-1786, DOI: 10.1002/esp.1657.
- Chu-Agor, M.L., G.A. Fox, R. Cancienne, and G.V. Wilson. 2008. Seepage caused tension failures and erosion undercutting of hillslopes. Journal of Hydrology 359 (3-4): 247-259, DOI: 10.1016/j.jhydrol.2008.07.005.
- Fox, G.A. 2008. Surface water and groundwater interactions: Investigating the connections. Centennial Session on Advances in Soil and Water Engineering, R.W. Skaggs (ed.), 2008 ASABE Annual International Meeting, June 30, 2008, 2 pages.
- Chu-Agor, M.L., R.M. Cancienne, G.A. Fox, and G.V. Wilson. 2008. Slope Failure Mechanisms due to Seepage: Three-Dimensional Soil Block Experiments. ASABE Paper No. 083771. St. Joseph, Mich.: ASABE.
- Cancienne, R.M., and G.A. Fox. 2008. Laboratory experiments on three-dimensional seepage erosion undercutting of vegetated banks. ASABE Paper No. 084107. St. Joseph, Mich.: ASABE.
- Fox, G.A., M.L. Chu-Agor, R.M. Cancienne, G.V. Wilson. 2008. Seepage Erosion Mechanisms of Bank Collapse: Three-Dimensional Seepage Particle Mobilization and Undercutting. American Society of Civil Engineers Environmental Water Resources Institute Annual Meeting, Honolulu, HI, May 12-17, 2008, 10 pages (CD-ROM).
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Progress 06/01/06 to 06/01/07
Outputs
Lysimeter experiments of groundwater seepage erosion have been performed with single layer noncohesive soils, layered bank profiles at Little Topshaw Creek, and layered bank profiles at Goodwin Creek. Lysimeter experiments have been performed with varying initial water content, hydraulic head, and bank slope conditions. The lysimeter experiments have resulted in the derivation of a seepage erosion sediment transport function which mimics excess shear stress equations. Predicting bank collapse due to seepage erosion undercutting has not been fully studied or modeled, even though its role in streambank erosion may be important. This research has developed a methodology for incorporating seepage erosion undercutting into bank stability models. A numerical finite element model, SEEP/W, was used to model soil-water pressure variations during seepage erosion observed in laboratory experiments with two-dimensional soil lysimeters. A general limit equilibrium bank stability
model called SLOPE/W was used to simulate bank stability with and without seepage erosion by comparing the computed factor of safety, Fs, at different stages of the seepage erosion process with regard to input parameter uncertainty using Monte Carlo analysis. The Fs converged to a specific value as undercutting progressed, suggesting that a stable bank can quickly become unstable when seepage undercutting is considered. For stable banks, the probability of failure reached 100% when the depth of the undercutting reached approximately 30 to 50 mm. This research verifies that the propensity of streambanks to fail during the recession limb of hydrographs may be the combined result of seepage erosion undercutting the streambanks and the reduced apparent cohesion of the bank. As a first attempt to evaluate the proposed seepage erosion sediment transport model and the proposed modeling strategy for seepage undercutting, slope destabilization driven by lateral, subsurface flow was studied
with uniform profile lysimeter experiments of two contrasting soil types (sieved sand and loamy sand) and with banks of varying slope. A slight modification of the existing sediment transport model adequately simulated seepage erosion in lysimeter experiments (especially for bank angles greater than 45 degrees) with both noncohesive soils without modifying the seepage parameters of the excess shear stress equation. The transport model was limited to predicting seepage erosion prior to small-scale bank failures on the bank slope. Integrated flow and bank stability models with the incorporation of bank geometry changes by seepage undercutting adequately represented large-scale bank collapse for banks with greater than 45 degree angles. For these lysimeter experiments, the role of seepage undercutting was equivalent to slightly greater than the role of increased soil pore-water pressure in leading to bank failure. The stability model could not predict small-scale sapping failures along
the bank slope due to the use of cylindrical or circular arc (in cross-section) slip surfaces. More complex stability approaches are needed to capture bank slope undermining.
Impacts
Select erosive events in many areas across the United States lead to high sediment loading in rivers and streams. This sediment loading must be addressed through riparian management. However, the range of possible solutions remains limited until we better understand the surface water/ground water interactions. This research has significantly extended theory on the role of ground water in erosion and provided new tools for multidisciplinary researchers to determine the importance of seepage erosion and undercutting for numerous soil, hydrologic, and environmental conditions. The initial integration of seepage undercutting into a bank stability model has provided guidance for developing a dynamic riparian simulation tool which will link bank stability with the adjacent, riparian groundwater system, leading to a critical tool for stability analyses in river rehabilitation.
Publications
- Wilson, G.V., R. Periketi, G.A. Fox, S. Dabney, D. Shields, and R.F. Cullum. 2007. Seepage erosion properties contributing to streambank failure. Earth Surface Processes and Landforms 32(3): 447-459.
- Fox, G.A., G.V. Wilson, A. Simon, E. Langendoen, O. Akay, and J.W. Fuchs. 2007. Measuring streambank erosion due to ground water seepage: Correlation to bank pore water pressure, precipitation, and stream stage. Earth Surface Processes and Landforms DOI: 10.1002/esp.1490.
- Fox, G.A., Chu-Agor, M.L., and G.V. Wilson. 2007. Erosion of noncohesive sediment by groundwater seepage flow: Experiments and numerical modeling. Soil Science Society of America Journal: In Press.
- Chu-Agor, M., G.V. Wilson, and G.A. Fox. 2007. Numerical modeling of bank instability by seepage erosion. Journal of Hydrologic Engineering (In Review).
- Wilson, G.V., G.A. Fox, and M.L. Chu-Agor. 2007. Seepage erosion impacts on edge-of-field gulley erosion. IV International Symposium on Gulley Erosion, Balboa, Spain, September 17-19, 2007, 2 pages.
- Fox, G.A., M. Chu-Agor, and G.V. Wilson. 2007. Seepage erosion: A significant mechanism of stream bank failure. American Society of Civil Engineers Environmental Water Resources Institute Annual Meeting, Tampa, FL, May 15-19, 2007, 14 pages.
- Fox, G.A., G.V. Wilson, R.K. Periketi and B.F. Cullum. 2006. A sediment transport model for seepage erosion of streambanks. Journal of Hydrologic Engineering, ASCE 11(6):603-611.
- Fox, G.A., M.L. Chu-Agor, and G.V. Wilson. 2007. Erosion of Noncohesive Sediment by Groundwater Seepage Flow: Experiments and Numerical Modeling. ASABE Paper No. 072235, ASABE: St. Joseph, MI.
- Chu-Agor, M.L., G.V. Wilson, G.A. Fox. 2007. Numerical modeling of bank instability by groundwater seepage flow. ASABE Paper No. 072117, ASABE: St. Joseph, MI.
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