DIKE FORMATION WITH SUBMERGED VANE

1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f…

DIKE FORMATION WITH SUBMERGED VANE

Submerged vanes are submerged foils constructed in a river at an angle of attack to induce horizontal circulation in the downstream flow. The initial height of vanes is 0.2 - 0.4 times the local water depth (d) at the design stage. Its length expressed as a multiple of the height to length ratio (H/L) normally is 0.25 to 0.5. With the use of a submerged vane in straight channels, dikes (heaps of sediment) were formed downstream. At an optimal angle of attack of 40o and at a Froude number of 0.25, the formation of the dike starts at some distance from the trailing edge of the rectangular and trapezoidal submerged vanes with a collar. A significant scour hole results at the trailing edge of a vane with a collar. A typical dike formed along the vane on the suction side with a symmetric bell-shaped profile. The dike formation phenomenon triggered by a vane close to the bank-line at a flow with a relatively higher Froude number, such as 0.25, does not seem to follow a straight alignment, but has a sort of curvilinear shape bent towards the suction side. The dike formation process for a flow with a smaller Froude number, such as 0.13, is observed to not be appreciable. With the same installation height of H, a vane without a collar was dislodged by the flow at a Froude number of 0.25, whereas it was stable at a Froude number of 0.13.