Comments on “Discharge coefficient of rectangular sharp crested side weirs part I: Traditional weir equation” by Bagheri, Kabiri-Samani, AR, and Heidarpour, M. Mojtaba Mehraein a,n , Masoud Ghodsian b a Kharazmi University, Tehran, Iran b Water Engineering Research Institute, Tarbiat Modares University,Tehran, Iran article info Article history: Received 5 March 2014 Received in revised form 27 May 2015 Accepted 1 June 2015 Available online 7 June 2015 Highlights  We compare the original paper equations with available data.  New equation is presented to estimate the discharge coefficient.  New equation can predict the discharge coefficient with higher accuracy.  New equation can be used in a wider range of non dimensional effective parameters. The authors are appreciated for a useful contribution regarding the hydraulics of flow over rectangular side weir. They have con- ducted series of experiments and used dimensionless parameters (i.e. F 1 , h 1 /p, b/B and h 1 /b) to predict the discharge coefficient. The authors stated that their proposed equations (i.e Eqs. (12) and (14) of the original paper) can predict the discharge coefficient with acceptable accuracy. They used their experimental data and stated that “the discharge coefficient of side weir correlates con- siderably with the Froude number, but slightly with h 1 /P”. The discussers used the experimental data of the original paper along with other experiments reported in the literature to evaluate Eqs. (12) and (14) of the original paper. Moreover sensitive analysis is conducted to address the effect of different parameters on dis- charge coefficient. The effect of h 1 /P on the discharge coefficient is studied in more details. General characteristics of sharp crested rectangular side weir data used in this discussion are shown in Table 1. Fig. (1) shows the variations of discharge coefficient with F 1 . The scatter of data confirms that in addition of F 1 other non-di- mensional parameters such as h 1 /P, h 1 /b and b/B also may affect the discharge coefficient of rectangular side weir. Two different statistical parameters R 2 and AAE (Eq. (1)) were used to evaluate the accuracy of the equations. AAE n c c c 100 1 i n d mea i d cal i d mea i 1 , , , ∑ = − () = ( ) ( ) ( ) where c d(mea,i) and c d(cal,i) are measured and calculated values of c d respectively and n is the number of available data. Table 2 shows the accuracy of the authors proposed equations (Eqs. (12) and (14) of the original paper) for all the data of Table 1. It is clear that the authors proposed equations (Eqs. (12) and (14) of the original paper) do not predict accurately the discharge for all data sources, especially for data of [2]. According to the dimensional analysis of the original paper, the following relation was assumed to estimate the discharge coeffi- cient of a rectangular side weir. ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ C k k h b k h p k b B F 2 d c c c c 11 2 1 3 1 4 1 2 3 4 = + + + () where k 1 –k 4 and c 1 –c 4 are empirical constants obtained using the experimental data. The empirical constants were derived by maximizing R 2 and minimizing AAE. The discussers proposed Eq. (3) to estimate the discharge coefficient for rectangular side weir. This modified equation predicts the discharge with AAE ¼ 8, R 2 ¼ 0.97 and can be used in the wider range of effective para- meters (Fig. 2). Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/flowmeasinst Flow Measurement and Instrumentation http://dx.doi.org/10.1016/j.flowmeasinst.2015.06.013 0955-5986/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: Mehraein@khu.ac.ir (M. Mehraein), Ghods@modares.ac.ir (M. Ghodsian). Flow Measurement and Instrumentation 45 (2015) 408–410