Design procedures and field monitoring of submerged barbs for streambank protection.
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2007-06-01
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OCLC Number:758675146
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Edition:Final report.
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Abstract:The main objective of this study was to evaluate the hydraulic performance of riprap spurs and weirs in controlling bank erosion at
the Southern part of the Raccoon River upstream U.S. Highway 169 Bridge utilizing the commercially available model FESWMS
and field monitoring. It was found based on a 2 year monitoring and numerical modeling that the design of structures was overall
successful, including their spacing and stability. The riprap material incorporated into the structures was directly and favorably
correlated to the flow transmission through the structure, or in other words, dictated the permeable nature of the structure. It was
found that the permeable dikes and weirs chosen in this study created less volume of scour in the vicinity of the structure toes and
thus have less risk comparatively to other impermeable structures to collapse. The fact that the structures permitted the
transmission of flow through them it allowed fine sand particles to fill in the gaps of the rock interstices and thus cement and better
stabilize the structures. During bank-full flows the maximum scour hole was recorded away from the structures toe and the scourhole
size was directly related to the protrusion angle of the structure to the flow. It was concluded that the proposed structure
inclination with respect to the main flow direction was appropriate since it provides maximum bank protection while creating the
largest volume of local scour away from the structure and towards the center of the channel. Furthermore, the lowest potential for
bank erosion also occurs with the present set-up design chosen by the IDOT. About 2 ft of new material was deposited in the area
located between the structures for the period extending from the construction day to May 2007. Surveys obtained by sonar and the
presence of vegetation indicate that new material has been added at the bank toes. Finally, the structures provided higher
variability in bed topography forming resting pools, creating flow shade on the leeward side of the structure, and separation of bed
substrate due to different flow conditions. Another notable environmental benefit to rock riprap weirs and dikes is the creation of
resting pools, especially in year 2007 (2nd year of the project). The magnitude of these benefits to aquatic habitat has been found in
the literature that is directly related to the induced scour-hole volume.
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