Laboratory evaluation of permeable triangular vanes with six-pillar elements placed in the outer bend of a 180° flume

Abstract

Extending the dimensions of the scour hole in the riverbank near the outer bank of meandering river which usually developed in the flat area can cause river bank failure and thus extensive damage to the surrounding area. In this study, the permeable triangular vanes (PTVs) made by six-pillar elements were implemented to evaluate the scour and sediment deposition in a 180° flume bend. Vanes with three different effective lengths were attached to the outer bank with space equal to five times the effective length and angle of 60° to the upstream. Three different effective lengths were tested under two different hydraulic conditions with the Froude numbers = 0.227 and 0.261. At the end of each experiment, the flume bed topography with laser meter was measured. To better compare the effect of vanes on the pattern of sediment distribution, two control experiments without the presence of vanes were also performed under the defined hydraulic conditions. The results showed that the permeable triangular vanes with the ratio of the effective length of vane (L) to the flume width (B) equal to 0.20 reduced the maximum scour hole and shift the scour from the outer bank to the nose of the vanes. For this case, the maximum depths of the scour were measured to be 19% and 45% of the flow depth and occurred at the nose of the fifth vane (at 66.75° location) at Froude numbers of 0.227 and 0.261, respectively. Moreover, the maximum height of the point bar above the bed on the outer bank was found to be equal to 30% and 31% of the flow depth at Froude numbers = 0.227 and 0.261, respectively. The results of this study improved previous studies conducted in the 90° bend and can be used as a guide for design purposes as an environmentally friendly countermeasure against bank scour in the bend of meandering rivers with gentle slope.