Location: National Soil Erosion Research Lab
Title: Using fluidized bed and flume experiments to quantify cohesion development from aging and drainage Authors
Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2013
Publication Date: September 26, 2013
Citation: Nouwakpo, S.K., Huang, C., Weltz, M.A., Pimenta, F., Chagas, I., Lima, L. 2013. Using fluidized bed and flume experiments to quantify cohesion development from aging and drainage. Earth Surface Processes and Landforms. DOI: 10.1002/esp.3477. Interpretive Summary: Soil cohesion, a measure of how soil particles adhere or stick together, has been related to soil erodibility, which measures how easy it is for soil particles to be detached by erosive forces. It has been known that many processes affect the development of soil cohesion, but there are no systematic ways of quantifying soil cohesion and its development. We modified the fluidized bed technique to measure soil cohesion by precisely controlling water flow through the soil until the force of the flow breaks the soil cohesive bonding. Using this technique, we quantified two processes that affect soil cohesion: aging and drainage. Aging is basically the natural development of soil cohesion when we let the soil stay saturated in water for some period of time. Draining water from the soil pulls soil particles together, hence accelerates the cohesion development. Comparing aging and drainage, we found that soil drainage has a more profound effect on soil cohesion, i.e., drainage increased soil cohesion 3 times higher in 24 hours as compared to aging for the same period. We further confirmed the findings from fluidized bed data on soil cohesion with a mini-flume study where soil erodibility was directly measured under flowing water. This research shows that we can use a simple and low cost fluidized bed procedure to quantify processes affecting soil erodibility which, in the past, has been a very costly and labor intensive endeavor.
Technical Abstract: Temporal variations in soil erosion resistance are often the result of a decrease in soil cohesion due to physical disruption followed by a regain of soil cohesion through a process analogous to a thixotropic sol-gel reaction also called aging, stabilization or consolidation. The goal of this study was to test the effectiveness of the fluidized bed method to detect changes in soil cohesion due to aging and to measure the effect of subsurface hydrologic conditions on soil cohesion development. The study used a flume experiment to validate results obtained from the fluidized bed method. Tests were performed on three different soils (a Miami soil, a Cecil soil and Crosby-Miami soil complex). Changes in soil cohesion due to aging and drainage state were successfully detected by the fluidized bed technique. For all soils tested, cohesion followed a parabolic curve where an increase in cohesion with time immediately after the soil was rewetted, was followed by a decrease in cohesion which often started after 24h of aging. When soils were aged at field capacity, the resulting cohesion measured by the fluidized bed method was on average 3.13 times higher than that measured when aging was done at saturation. Trends in soil rill erodibility Kr with time measured in the flume experiment were consistent with the parabolic pattern observed in soil cohesion estimates but the legacy effect of suction applied at field capacity faded after 72h of aging.