Experimental analysis of flow-altering countermeasures against local scour around spur-dike structures

Behshad Mohajer Iravanloo, Mojtaba Saneie, Hooman Hajikandi

Monday 29 june 2015

14:20 - 14:35h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 2A. Sediment - Erosion

Construction of spur-dike structures or bridge abutments in river streams may decrease the channel width and lead to a shear distribution change from upstream to downstream and result in bed erosion. The stability of spur-dike structures in rivers may be decreased due to a significant amount of local scour around them. High intensity turbulent flow and formation of wake vortices near the structure are main causes of local scour. Flow-altering devices could be used as scour countermeasures to reduce the strength of turbulent flow around these structures, by reducing approaching flow intensity. In the present study, roughening elements and sacrificial piles were experimentally investigated with different geometric arrangements for a spur-dike structure. The aims of this study are to reach the most desirable geometric parameters which would reduce the maximum scour depth and volume of scour. Three different spacings for roughening elements and three different kinds of sacrificial piles in number and distance from spur-dike upstream face were examined. Also, a comparison of these were presented. The experiments were conducted in clear water conditions with uniform sediment of d50 =1.86 mm. Results shows that under limitation of this study, sacrificial piles are more effective than the roughening elements in case of spur-dike countermeasures. Moreover, use of sacrificial piles reduced the maximum scour depth and scour volume from (34 % to 70 %) and (31 % to 74 %) respectively. Also, results indicate that the effectiveness of sacrificial piles is a strong function of their geometric arrangement.