An Experimental Investigation on the Effective Factors of Local Scouring Reduction around T-Shaped Bandal-Like Groynes

The ecosystem and equilibrium of rivers can be significantly affected by the river bank erosion which can also limit the human access to the rivers. Groyne is an important river restoration structure that prevents bank erosion through deviation of flow from the river banks to the main channel. From the permeability aspect, these structures can be classified into three types of permeable, impermeable, and bandal-like ( hybrid type which includes permeable and impermeable types ). Moreover, these structures can be categorized to straight, T-shaped, and L-shaped configurations. This research aims to investigate the local scour around a new type T-shaped bandal like groyne. The total number of 66 experiments were conducted through a straight flume ( 12 m length, 0.6 m width, and 0.6 m depth ) under non-submerged and clear water conditions. T-shaped bandal like and T-shaped impermeable groyne structures were fabricated in three web to wing length ratios of 0.5, 0.75, and 1. Also, three upstream to downstream wing ratios of 0.5, 1, and 2 and the permeabilities of 33%, 50%, and 60% were selected for the T-shaped banal like structure. The experiments were carried out at the flow discharge of 6 Ls-1, 9Ls-1, 12 Ls-1 and 15 Ls-1 in the presence of the T-shaped impermeable groynes and the T-shaped bandal-like groynes. It was revealed that, increasing the structure permeability resulted in decreasing of the maximum relative scour depth. Under 33%, 50%, and 60% permeabilities of the T-shaped bandal-like groynes, the maximum scour depth was decreased by 63%, 78%, and 83%, respectively compared to the T-shaped impermeable groynes. Moreover, it was observed that the maximum relative scour depth was increased by the average of 46% as for the greater values of structure length. The maximum relative scour depth was also increased for the greater values of flow discharge. It was found that there is no relationship between the maximum scour depth and the ratio of upstream wing length to the downstream wing length of groyne. Based on the results, the permeability and length of the groynes and the flow discharge are among the factors affecting local scouring around T-shaped bandal-like groyne. The significant decrease in the relative scour depth in T-shaped bandal-like groynes compared to T-shaped impermeable groynes indicates that the T-shaped bandal-like groynes have better performance than the impermeable ones in scouring control, structural stability and river bank protection.