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ARS Home » Research » Publications at this Location » Publication #84424
Title: STRESS MEASUREMENT UPSTREAM OF AN OVERFALL

Author
item Robinson, Kerry
item Cook, Kevin

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Gully erosion is a serious problem, and many factors influence the way gully erosion happens. The forces transmitted to the soil surface change as flowing water accelerates toward an abrupt drop or overfall. These forces or stresses can have a big influence on how quickly and in what manner an overfall moves upstream. Measuring these boundary stresses for different flow conditions helps provide an improved understanding of gully erosion. The stresses were found to increase as the flow increased, and these stresses were a maximum at the overfall. The stress changes were described for a number of different flow conditions, and an equation was developed to predict these stresses. While primarily of interest to researchers, this information should also be of interest to design engineers. This material can be used to determine the forces upstream of an overfall that contribute to gully erosion.

Technical Abstract: The hydraulic shear stress was measured in time and space on the channel bed upstream of an overfall brink. A hot-film anemometer was used to obtain stress measurements in a fixed-bed model for Froude numbers ranging between 1 and 4. The time-averaged stress was observed to increase as the flow accelerated toward the brink. The brink stress typically increased as the flow rate and Froude number increased. For a given flow condition the stress magnitude was a maximum at the brink. This stress decreased to a constant value relatively rapidly with movement away from the brink. The distance required to transition from the peak brink stress to the constant stress value decreased as the Froude number increased. A relationship was developed and validated that predicts the boundary stresses upstream of the overfall brink. The observed variations in stress magnitude can influence gully headcut erosion.