Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2006
Publication Date: 6/1/2007
Citation: Rieke-Zapp, D., Poesen, J., Nearing, M.A. 2007. Effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion. Earth Surface Processes and Landforms. 32:1063-1076. Interpretive Summary: Rocks in the soil profile have a dramatic effect on soil erosion, both in terms of how much erosion occurs during a rainstorm and where it occurs on the landscape. In certain environments the effect of rocks can be very dominant. In this study we looked quantitatively at the impacts of rocks on erosion rates. We did this by placing soil with different amounts of rocks added in a controlled laboratory flume and measuring the soil that was eroded and the shapes of the rill patterns that formed. We found that rate of erosion dropped dramatically with a very small presence of rocks. We also found that rills forms in the soil with rocks were much wider, and flow depths much less than in soil without rocks. We will use this information to develop algorithms for computer-based soil erosion models that are used to predict soil erosion in different environments. These models are used for helping farmers and ranchers develop soil conservation plans on the land, for engineering design purposes, and for implementing national soil conservation programs. Thus, this study will lead to better soil conservation planning tools for the United States.
Technical Abstract: Rock fragments can act as a controlling factor for erosional rates and patterns in the landscape. Thus, the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix have on concentrated flow hydraulics and erosion . Laboratory flume experiments were conducted with soil material that was mixed with rock fragments. Rock fragment content ranged from 0 to 40% by volume. Other treatments were slope (7 and 14%) and flow discharge (5.7 and 11.4 l min-1). The more rock fragments were mixed with the soil, the less sediment yield was observed at the outflow. Rock fragment cover at the soil surface, i.e. surface armour, increased with time in experiments with rock fragments. With increasing rock fragment content total sediment yield decreased and width of flow became wider. Flow energy was largely dissipated by rock fragment cover. For more turbulent flow conditions when roughness elements were submerged in the flow, hydraulic roughness was similar for different rock fragment contents. In experiments with little or no rock fragments a narrow rill incised. Flow energy was dissipated by headcuts. Total sediment yield was much larger than for experiments with rock fragments in the soil. Depending on inflow conditions, just a small amount of rock fragments was necessary to reduce sediment yield to a negligible amount.