Free Overfall for Discharge Measurement in Channels of Different Shapes: A Review

Abstract

The end drop in open channels can be considered as a simple and useful tool for the measurement of flow rates flowing in open channels of different shapes. The depth at channel end can be related to the critical depth in the approaching channel and denoted as (EDR). The (EDR) is an essential parameter for measuring end drop discharge (EDD) in open channels. The main target of this paper is to review the previous works done on the end drop in different shapes of channels using the properties of the free end drop flow as basic criteria for the estimation of (EDR) and (EDD). Useful relationships between (EDR) and channel slope are presented which are the outcome results of previous researches done on smooth and rough open channels of different shapes (rectangular, trapezoidal, circular and triangular). Moreover, the correlations of (EDD) depending on end drop depth and characteristics of the upstream approaching channel are presented for channels of different shapes for subcritical and supercritical states of flow. Still there is no unique theoretical solution for the problem of using end depth of free drop as a key for the estimation of flow rates in open channels which needs more theoretical and experimental studies and works on this important field of research.