Experimental Study on Scouring Depth by Free Overfall Downstream of Irrigation Weirs

Many weirs for irrigation are distributed in upstream area of river fans. They have risks of piping and structural unstableness by their downstream scouring from downstream riverbed declination that occurred by riverbed excavation. Severe damage of weirs is caused by less frequent large floods. It is required to make maximum scouring depth right downstream of the weir apron through less frequent large floods clear for the protection of weir from damages caused by the large floods. In this paper, the scouring depth and mechanism in site conditions of irrigation weirs was evaluated by two-dimensional hydraulic model experiments. Scouring proceeded with fluctuated scouring depth and flow regimes between wavy flow and submerged jet flow. Temporal changes in maximum scouring depth was calculated within an error of 10% by proposed experimental formulas in this paper.