development of a computer model for long-throated flumes based on manning equation and different side slopes of trapezoidal channels

Measurement of irrigation water in agricultural areas is necessary, especially, in arid and semi-arid regions. long-throated flumes have been used to measure irrigation water and are known to be inexpensive devices with high performances. in these structures, head-discharge tables are predicted theoretically with no need to calibrate. in this study, the model of lotf (long throated flumes) was developed in vb. net programming language, in which, friction head loss and h-q (h is head at measuring station and q is discharge) tables were predicted by using the manning's equation. the predicted tables of h-q by the lotf model were perfectly similar to the results of win flume and hec-ras model which are universally used for these flumes and open channel flow, respectively. calculated h-q tables in trapezoidal flumes with two different side slopes of 0 and 1, 0 and 2, and 0 and 4 were computed by the lotf and hec-ras models and were the same as those predicted by the winflume model with equal average of these side slopes of channel. at a water depth, in trapezoidal sections with different and equal average side slopes, the resulted h-q tables in the three models were the same.