عنوان مقاله [English]
Due tothe high cost and the need for Experts to use advanced flow measuring equipment in canals, the use of simple, inexpensive and low-cost methods has always been considered by researchers and operating companies of irrigation and drainage networks. In this study, flow measurement in canals has been investigated experimentally using trapezoidal flumes with cylindrical pier in four side slopes. By measuring the flow depth at upstream and downstream of the flume throat, separate relationships and graphs were obtained to calculate the discharge at each studied side slopes on the base of functional relationships (both in free and submerged flow conditions). Also for the studied side slopes, one relation for free flow conditions and two relations for submerged flow conditions were obtained. Mean absolute relative error (MARE) for calculation of dimentionaless discharge using the obtained relationships under free flow conditions was obtained 6.2, 4.6, 8.1 and 9.4%, and under submerged flow conditions was obtained 25.17, 22.9, 19 and 14% respectively in side slopes (z) of 1, 0.7, 0.4663 and 0.268. The value of MARE for calculation of dimensionless discharge using the obtained relation for all studied side slopes was obtained 8.2% under free flow conditions and 35.9 and 34.3% under submerged flow conditions (using two related equations). The maximum root mean square error (RMSE) for calculation of dimensionless discharge for the all studied side slopes, was obtained 0.078 under free flow conditions and 0.34 and 0.38 under submerged flow conditions (using two related equations). Then, using the related relation to each side slope (separately) has less error compared to using a relation for all side slopes.