Asian Journal of Water, Environment and Pollution, Vol. 13, No. 2 (2016), pp. 29–38. DOI 10.3233/AJW-160014 Open Channel Discharge Measurement Using 0.127 Metre (5 Inch) Long-Throat Flume Milan Nayek, Rajib Das*, Subhasish Das, Prasun Dutta and Asis Mazumdar School of Water Resources Engineering, Jadavpur University, Kolkata 700032, West Bengal, India * rajibdas79@gmail.com Received September 10, 2015; revised and accepted March 29, 2016 Abstract: Long-throat fumes are used in fow measurement by developing power curve relationship between water depth and discharge. This structure provides economical and fexible water measurement capabilities for a wide variety of open-channel fow situations. The advantage of these structures includes minimal head loss, low construction cost, adaptability to a variety of channel types, and ability to measure wide ranges of fows with custom-designed structures. A series of detailed laboratory measurements were made under steady-state fow conditions through a Long-throat fume of control section width 0.127 m (5′′) as there is no data available for 5′′ for any fume length. Free fow and submerged fow calibration were done within fow range 0.005 m 3 /s to 0.022 m 3 /s. The result of the calibration shows discharge within calibrated fow range. The proposed equation can determine accurately the discharge with maximum deviation of +6% and +8% for stilling well and gauge data respectively. Henceforth, using proposed equations Ditchrider’s table and rated graph was developed for feld implementation of the fume. Key words: Flume, submerged fow, free fow, Ditchrider’s table. Introduction Water demand increases with every step towards urbanization and industrialization. In agriculture sector, water requirement is also increased because of genetically modifed organisms and high yielding crops. Resulting to this, proper water distribution and measurement is necessary for ef fcient water management. To ensure accurate measure of supply water, measurement devices should be employed which are durable, low-cost, transportable and easy for installation. Structures like fumes are often used for the discharge measurement in open channels in the small irrigation canals and felds. Flumes can be categorized in two groups: • Short-throat fumes • Long-throat fumes *Corresponding Author Short-throat fumes are so called because they have small length of control section such as Parshall fume, cut-throat fume, H fume etc. They have lower head loss and of passing the sediment on through but are more costly to fabricate and install. Non-level fumes and improper installation (insuffcient crest height) are the most common problems. However, cut-throat fumes (Hyatt, 1965; Skogerboe, 1967; Temeepattanapongsa, 2012; Das et al., 2015) are simpler to construct and can operate as free fow conditions at a higher degree of submergence. Long-Throat Flumes Long-throat fumes are coming into general use because they can be easily ftted into complex channel shapes as well as simple shapes (Replogle, 1975; Bos et al., 1991). Long-throat fumes have many advantages compared to