|NIEBER, JOHN - University Of Minnesota|
|SIDLE, R - Us Environmental Protection Agency (EPA)|
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 8/11/2012
Publication Date: 9/18/2012
Citation: Wilson, G.V., Nieber, J., Sidle, R.C. 2012. Internal erosion during soil pipe flow: Role in gully erosion and hillslope instability. ASABE Annual International Meeting. CD-Rom Proceedings of the 18-21 September 2011 Conference Hilton Anchorage, Anchorage Alaska. pp 1-8.
Interpretive Summary: Many people have observed dam and levee failures, landslides, and gully erosion and speculated that they were caused by water moving below the surface causing erosion below ground in a process called piping. While these reports agree on the general idea of piping, there has not been agreement on the specific subsurface flow and erosion processes involved and one of the problems has been that many different and confusing terms have been used to describe the processes. One piping process that has reported a lot from field observations involves flow through a large pore that erodes on the inside until it resembles a soil pipe. However, very little experimental research has been done to understand this process or measure the rats of flow the the soil pipe or the erosion taking place on the inside of the soil pipe. Questions exist as to the conditions under which flow through soil pipes: result in internal erosion, make hillslopes stable by acting as drain pipes, make hillslope unstable by causing pressure buildups in the soil, or result in gullies forming in new locations or reforming in old gullies that had been filled in with soil. The objective of this paper was to review differences in the term used to better explain the piping processes and highlight the experimental work that has been done on the specific processes of flow through soil pipe and erosion inside pipes. The studies reviewed include those that examined the process of slope stability as affected by the clogging of soil pipes, the process of gullies reforming due to mass failures caused by flow into soil pipes closed off by filling gullies with soil, and the process of gullies forming by the soil above a soil pipe collapsing because the pipe got so big by erosion inside that the soil above the pipe could not be supported. In some of these studies the soil pipes were created using tubes with holes in them placed in the soil, while in other studies the soil pipes were formed in the soil by removing a rod thereby leaving an open channel in the soil. These studies will be described and gaps in our understanding of pipe flow and internal erosion processes and our ability to model these processes will be discussed.
Technical Abstract: Many field observations have lead to speculation on the role of piping in embankment failures, landslides, and gully erosion. However, there has not been a consensus on the subsurface flow and erosion processes involved and inconsistent use of terms have exasperated the problem. One such piping process that has experienced a lot of field observations but very limited mechanistic experimental work involves flow through a discrete macropore or soil pipe. Questions exist as to the conditions under which preferential flow through soil pipes: result in internal erosion, stabilize hillslopes by acting as drains, result in hillslope instability by causing pressure buildups, result in ephemeral gully formation or reformation of filled-in gullies. The objective of this paper was to review discrepancies in terminology to better explain the piping processes and highlight the experimental work done to date on the specific processes of soil pipeflow and internal erosion. The studies reviewed include those that examined the process of slope stability as affected by the clogging of soil pipes, the process of gullies reforming due to mass failures caused by flow into discontinuous soil pipes, and the process of gully initiation by tunnel collapse due to pipes enlarging by internal erosion. In some of these studies the soil pipes were simulated with perforated tubes placed in the soil, while in other studies the soil pipes were formed out of the soil itself. These studies will be described and a discussion will ensue that considers the gaps in our understanding of pipe flow and internal erosion processes and our ability to model these processes.