Excessive sediment is one of the most common surface water pollutants across the world with a majority of sediment originated from streambanks in many watersheds. In predicting sediment transport, the interacting role between surface water and shallow ground water is not well understood. The importance of ground water seepage and piping is unknown with respect to other fundamental processes of river erosion, although seepage and piping features are observed on streambanks throughout the world that span a range of geomorphologic conditions. Specific seepage and piping mechanisms that cause bank failure may never manifest themselves as transparent features on unstable banks.
This research hypothesizes that multiple ground water flow mechanisms, combined with fluvial processes, affect the occurrence and timing of streambank erosion and failure. Ground water forces can act over extended periods to destabilize banks between flow events. Specific seepage mechanisms become prevalent under certain predictable streambank stratigraphy and hydrologic conditions. This research is currently conducting three-dimensional soil column experiments to accomplish the following objectives: (1) determine the occurrence and prevalence of different seepage erosion mechanisms (i.e., seepage gradient forces and undercutting); (2) derive a sediment transport equation for seepage erosion across a range of soil textures and cohesions; (3) identify typical undercut formations when seepage undercutting occurs; and (4) determine the sequence of erosion steps leading to failure by ground water flow through soil pipes. Laboratory experiments combining three-dimensional soil columns and small-scale, recirculating, indoor flumes are quantifying the impact of seepage on a bank?s resistance to fluvial erosion and determining the role of vegetation in preventing bank weakening by subsurface/fluvial processes. The hypotheses affirmed/falsified by the laboratory experiments are being examined at the field scale through innovative field experiments. Two field sites in Oklahoma are being instrumented to monitor natural fluvial shear stresses, pore-water pressures, and gradient forces over several months prior to a controlled seepage induced failure experiment.
This research has implications for understanding and implementing successful riparian management programs and erosion mitigation policies in the United States and abroad. Issues such as streambank stability and sediment load to streams have been major concerns for decades and billions of dollars have been spent on streambank protection and restoration. This sediment loading must be addressed through riparian management. However, the range of possible solutions remains limited until we better understand the surface/ground water interactions. This project aims to strengthen student research and mentoring skills as well as build faculty and student experience, publications, and networks in the United States and abroad. A primary strength of this proposal is the continuation of established partnerships between an academic institution (Oklahoma State University) and a federal government agency (USDA-ARS National Sedimentation Laboratory). This research is being disseminated to high school students across Oklahoma, including typically underrepresented students in engineering (i.e., rural, women, and Native American students), through a unique soil erosion contest associated with the Future Farmers of America (FFA) Career Development Events.
Intellectual Merit: Excessive sediment is one of the most common surface water pollutants, diminishing water quality in both the stream and river and especially in water supply reservoirs. In predicting erosion of streambanks, the interaction between surface water and shallow ground water is not well understood. This research investigates ground water, and more specifically seepage and piping, as causes of streambank erosion and failure. Seepage and piping features are observed on streambanks throughout the world. This research tested a state-of-the-art streambank erosion and failure computer model called the Bank Stability and Toe Erosion Model (BSTEM). The modeling capability demonstrated by this research further supports the use of computer-based modeling in streambank stabilization and river restoration projects. Groundwater erosion experiments were conducted in the laboratory to determine the occurrence of groundwater erosion in causing streambanks and hillslopes to erode and collapse. Procedures were derived and evaluated to help engineers and geomorphologists identify the prevalence of groundwater erosion on streambanks and hillslopes. Field sites in Mississippi and Oklahoma were instrumented to conduct controlled groundwater erosion and streambank failure experiments. Groundwater erosion was shown to be an important mechanism of streambank erosion and failure, especially when acting in concert with streamflow that eroded streambank sediment and prevented self-healing of the groundwater seeps. An improved erosion model for calculating streambank erosion by both streamflow and groundwater was developed and evaluated. Also, procedures to derive the parameters values for variables in this erosion model were also derived using a submerged jet erosion test (JET) device. This new erosion model has the potential to transform the estimation of erosion on hillslopes, embankments, gullies, streambeds, and streambanks. Broader Impacts: Streambanks are some of the most vulnerable geologic structures on earth. Riverbank erosion and land loss are resource management problems of global significance. Issues such as streambank stability and sediment load to streams have been major concerns for decades and billions of dollars have been spent on streambank protection and restoration. Too much sediment in our water results in taste and odor problems and can shield bacteria from the action of disinfectants during water treatment. Sediment deposition on streambeds and lake bottoms reduces spawning areas, aquatic organism food sources, and habitat complexity. An improved understanding of erosion processes generated from this work will aid in the design of improved stabilization practices for streambanks. Also, the research partially supported graduate degrees for two Ph.D. students and two Master of Science students at Oklahoma State University. Student water conferences were held in April 2012 and April 2013 where students presented their research in front of other students, faculty members, and guests. Approximately 40 students presented their research at the 2012 Student Water Conference on the Oklahoma State University (OSU) campus. Students from both OSU and outside of OSU, including Auburn University, Nebraska-Wesleyan, Texas A&M University, University of Arkansas, University of Kentucky, and the University of Missouri, participated in the conference. The conference included a keynote lecture by Dr. Glenn Brown, Regent’s Professor, OSU, on Henry Darcy. Approximately 45 undergraduate and graduate students presented their research at the 2013 Student Water Conference in April 2013. Students from both OSU and outside of OSU, including Auburn University, New Mexico State University, Penn State University, Tarleton State University, Texas A&M University, University of Arkansas, University of Hawaii, University of Kentucky, University of Nebraska, University of Oklahoma, and Virginia Tech University, participated in the conference. The conference was also supported by funds through the Orville L. and Helen L. Buchanan Endowed Chair in Biosystems and Agricultural Engineering. The conference included a keynote lecture called the Buchanan Lecture by Dr. Glenn Wilson, Soil Physicist/Hydrologist, at the USDA-ARS National Sedimentation Laboratory in Oxford, MS. The Buchanan Lecture was titled "From Soil Physicist to Research Hydrologist: Be Prepared for Non-Laminar Career Flow Paths". The conference also welcomed back Dr. Derek Heeren, a recent Ph.D. graduate from Oklahoma State University, for a presentation on "Perspectives on Different Phases of a Water Career". Dr. Heeren discussed his experiences in entering industry immediately after a B.S. degree, returning to graduate school and completing a Ph.D. degree, and his experiences as a first year faculty member in academia. Dr. Heeren joined the faculty at the University of Nebraska-Lincoln in August, 2012, as an Irrigation Engineer and Assistant Professor. A graduate student (Master of Science student) participated in a unique mentoring program with the USDA-ARS National Sedimentation Laboratory over a three-month period, gaining a wealth of experience related to monitoring and modeling sediment transport processes. Also, the project supported undergraduate research assistants in working with the graduate students on their projects, including several that are now pursuing advanced engineering degrees in graduate school.
