Ground Water Seepage and Piping Mechanisms of Streambank Erosion and Failure

Oklahoma State University, Stillwater OK

Investigators

Abstract

Ground Water Seepage and Piping Mechanisms of Streambank Erosion and Failure 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.