Abstract
Many devices are fabricated to measure discharge in circular open channel. The flow over a free overall (brink phenomenon) can be used as a device to measure discharge in open channels with known the end depth. This paper presents mathematical and experimental studies to evaluate efficiency of the brink as device of measuring low flow rate in horizontal, mild and adverse circular open channels. The general mathematical model is derived using momentum, discharge and Froude number equations for horizontal, mild and adverse slopes for circular open channels. A proposed mathematical model is calibrated by previous and present experimental data. Equation gives accurate discharge from known end water depth is presented. The results of the laboratory experiments showed that the circular flumes can be successfully used to measure the low flow rate in open channels. A relationship of discharge to the end depth for horizontal smooth circular open channels is proposed.