Brink Depth in Nonaerated Overfalls

Abstract

Small drop structures employed in irrigation canals are often not ventilated. In this paper the importance of the residual pressure at the brink of a rectangular overfall is quantified by means of the 1‐D momentum equation. The pressure acting below the nappe under nonaerated conditions is studied experimentally and correlated to the drop height in nondimensional terms. Comparison is made with relevant results for ventilated drop structures and criterion for defining a low drop is proposed. The results of pressure estimates are then used for a theoretical evaluation of the brink depth ratio as a function of the nondimensional drop height. The theoretical predictions are found to be in good agreement with the experimental results.