Sediment detachment and transport processes associated with internal erosion of soil pipes

Abstract

Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd.

Rainfall Induced Erosion Assessment on Hill Slope of GCE

“…The disturbance of soil during construction activity is considered as a major non-point source (NPS) of water pollution by sedimentation [10][11][12]. Thus, construction activity is ultimately liable for the exclusion of topsoil, destruction of vegetation, surface runoff and soil erosion [13][14][15][16][17]. Based on the rate of sedimentation loading, surveyed throughout the US, the significance of erosion by construction sites was reported by the Azamathulla and Ghani [18].…”

Modeling Internal Erosion Processes in Soil Pipes: Capturing Geometry Dynamics

“…In fact, flow velocities in soil pipes have been shown by dye tracing to be in the range of streamflow velocities and, like streams, the flows can be highly turbulent (Wilson et al, 2016; Zhou et al, 2016). Wilson et al (2018) stated in a summary of hydrodynamic processes involved in pipe flow that “pipe flow velocities can exceed surface flow velocities because the flow is concentrated into a small conduit whereas surface flow can spread out with vegetation and other roughness features slowing the surface velocity.” As a result of these large pipe flow velocities, shear forces readily exceed the frictional strength binding soil, which results in detachment of particles and aggregates. The resultant internal erosion not only enlarges the pipe such that it can handle greater flow velocities but also can enhance the pipe network's contributing area and connectivity, which Wilson et al (2016) termed a self‐propagating process.…”

“…This is despite their finding that piping has been reported in “almost all climatic zones of the world,” all landforms, 20 of the 28 soil types, and “almost every soil texture.” Despite the ubiquitous nature of piping, very little work has been done on erosion by pipe flow (Fox and Wilson, 2010). In a review on internal erosion by pipe flow, Wilson et al (2018) reported that only 7% of the papers published in the last two decades on soil pipes dealt with sediment transport. They found that “none were controlled experimental studies on the processes involved, such as mechanisms of particle or aggregate detachment from pipe walls or transport, filtering (physical entrapment) or sorption/flocculation and sedimentation of the particles.”…”

“…Beven and Germann (2013) reviewed the progress made on preferential flow in the last 30 yr since their classic paper (Beven and Germann, 1982) on macropore flow. Despite the enormous body of work since that time on macropore flow and preferential flow in general, they concluded that “the topic has still not received the attention that its importance deserves.” Even with the proliferation of research on preferential flow in the last three decades, Wilson et al (2018) found that only 1% of the studies on macropores in the last two decades “dealt to any degree with particle detachment and sediment transport.” It is no wonder that erosion models do not include pipe flow processes; given the scarcity of studies on the processes involved, it is difficult to mathematically represent processes that are so poorly understood and quantified. Wilson et al (2018) supplemented the literature on sediment detachment and transport in macropores and soil pipes with extensive research conducted on streams and man‐made (industrial) pipes to better understand the processes involved.…”

“…Despite the enormous body of work since that time on macropore flow and preferential flow in general, they concluded that “the topic has still not received the attention that its importance deserves.” Even with the proliferation of research on preferential flow in the last three decades, Wilson et al (2018) found that only 1% of the studies on macropores in the last two decades “dealt to any degree with particle detachment and sediment transport.” It is no wonder that erosion models do not include pipe flow processes; given the scarcity of studies on the processes involved, it is difficult to mathematically represent processes that are so poorly understood and quantified. Wilson et al (2018) supplemented the literature on sediment detachment and transport in macropores and soil pipes with extensive research conducted on streams and man‐made (industrial) pipes to better understand the processes involved. From this review, they recommended that future research needs to: “develop mechanistic mathematical expressions for describing soil detachment within soil pipes that account for seepage gradient forces and effects of gravity on pipe walls and roofs; and develop models capable of simulating the mechanics of sediment detachment, transport, and deposition in soil pipes, and associated changes in the geometry of soil pipes, as well as collapse of pipes to form gullies.”…”