SCOUR AROUND SUBMERGED VANES IN A CURVED CHANNEL

Abstract

Increasing capital costs, emerging environmental concerns and rising maintenance expenses of the conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured for control of sediment movement, scour and deposition. The submerged vane functions through generation of secondary circulation for bringing about desired sediment redistribution within the channel cross-section. The strength of secondary circulation is profoundly influenced by the magnitude of the incident angle of vane to the approach flow direction. All previous researches on submerged vanes were performed in either straight or mildly curved channels with single bend with band angle in the range of 90° to180°. No submerged vanes study, so far, has been done in the curved channel having two consecutive meanders which is generally observed in the field. In this dissertation work experiments were conducted in a curved channel having two consecutive meanders with the parallel and zigzag arrangements of the submerged vanes. Study of variation of scour around the vane and the effect of various vane parameters like Os (streamwise centre to centre vane spacing), 01, (vane edge to bank distance), 6„ (transverse centre to centre vane spacing), H/L (aspect ratio) etc. on the scour has been carried out. For this, 50 m wide mobile bed flume with two bends was constructed in the river model tray of the laboratory. The experimental programme was organized in three phases. In the first phase (Run 1A), experiments were performed in a 50 cm wide mobile bed flume, to study the scour in the bend portion in the transverse direction. In the second phase (Run 1B), experiments were performed in the flume using submerged vanes with parallel arrangement and studied the scour in the bend portion in the transverse directions with constant angle of attack (a =300), with varying degree of submergence, aspect ratio, streamwise spacing in an array of vanes, transverse spacing in the vane array and bank to vane spacing.