Study of Scour and Flow Patterns around Triangular-Shaped Spur Dikes
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-2261-x
Hydraulic Engineering
Study of Scour and Flow Patterns around Triangular-Shaped Spur Dikes Mohammad Bahrami-Yarahmadi
a
, Stefano Pagliara
b
, Elham Yabarehpour
c
, and Noushin Najafi
c
a
Dept. of Water Structures, Faculty of Water Science Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran DESTEC- Department of Energy, Systems, Territory and Construction Engineering, University of Pisa, Pisa 56122, Italy c Faculty of Water Science Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran b
ARTICLE HISTORY
ABSTRACT
Received 16 December 2019 Revised 23 April 2020 Accepted 29 May 2020 Published Online 24 August 2020
River bank erosion can upset the balance of the river and its aquatic habitat, as well as the lands and facilities adjacent to the river. As hydraulic structures, spur dikes are constructed perpendicularly to erodible river banks in an attempt to divert the flow toward the middle of the channel as a measure for reducing and controlling river bank erosion. The expansion of the scour hole at the tip of the spur dike can lead to structure failure. Inclining the horizontal crest of the rectangular spur dikes (called triangular-shaped spur dike) can reduce the scouring at their tips. There are limitations on the design criteria for this newly-introduced structure. In the present study, the scour patterns developed around triangular spur dikes were examined under different hydraulic conditions and compared these patterns with those obtained for common type of spur dikes (rectangular spur dikes). The three-dimensional velocity components around triangular and rectangular spur dikes were also measured. According to the results, maximum scour hole depth and volume were smaller in the triangular spur dikes than in their rectangular counterparts. Quantitatively, on average, maximum scour hole depth and volume in the former were, respectively, 44% and 70% less than those in the latter. Based on the analyzed the flow patterns, it is recommended that the spacing between the triangular spur dikes should not exceed 5.5 times the effective length of the structure.
KEYWORDS River bank erosion Scour hole Rectangular spur dike Triangular spur dike Straight river
1. Introduction Groins or spur dikes are built on river banks in an attempt to reduce river bank erosion, prevent lateral migration of the river, improve navigation conditions in the river, divert the flow toward river intakes, and revive or improve aquatic life in the river. They typically are constructed perpendicular to the river bank, thus diverting the flow away from the bank toward the middle of the channel and reducing the flow velocity near the bank. The Memphis and Vicksburg Districts in the United States use perpendicular spur dikes (Copeland, 1983; Klumpp and Baird, 1992; Julien, 2002; Zhang et al., 2012). Numerous studies have been conducted on spur dikes along straight and meandering rivers for the purpose of identifying the flow as well as
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