Orouji et al. (2012) utilised simulated annealing (SA) and shuffled frog leaping algorithm (SFLA) algorithms to calibrate the parameters of the non-linear Muskingum model. The study is both appropriate and interesting, especially for the application of SFLA, but the discusser would like to draw attention to two points -flood routing model classification and storage equation selection. Orouji et al. (2012) indicated that there are two general procedures to route the hydrograph of flooding along river reaches -hydraulic (i.e. distributed) and hydrologic (i.e. lumped) routing procedures. However, not only one-dimensional (1D) and 2D distributed flood routing models (Akbari and Barati, 2012;Xia et al., 2012) and lumped flood routing models (Barati, 2011) can be used to route the hydrograph of the downstream section, but semi-distributed models such as Muskingum-Cunge procedures (Barati et al., 2013;Perumal and Sahoo, 2007) can also be used. et al. (2012) used the data of Karoon River as a real case study. However, the use of a non-linear model for this dataset is questionable. Selection of the storage equation is based on the relationship between weighted flow (i.e.
Classification of flood routing models
Selection of storage equationOrouji[XI t + (1 À X)O t ] where I t and O t are the inflow and outflow at time t, respectively, and X is the weighting factor) and storage volume (Yoon and Padmanabhan, 1993) by considering the features of catchments (e.g. area, shape, morphology, lithology and vegetation) and the features of flood and rainfall events (e.g. rainfall intensity and duration) that affect the relationship. Because the second case study of the original paper, unlike the first one, does not have a non-linear relationship (see Figure 9), use of a linear model might be more appropriate. The routing equation of the linear model can be developed by combining Equations 1 and 2 of the original paper. Although several methods are available for determining the parameters of the linear model (Yoon and Padmanabhan, 1993), the least-squares method (LSM) of Aldama (1990) is used here.In the original paper, the SFLA has better results than SA in terms of statistics. The best results of the SFLA, for the second case study, in ten runs were j sum of the square deviation of observed and computed outflows (SSQ) ¼ 130 928 . 6473, the absolute value of the deviations of the peak of computed and observed outflows (DPO) ¼ 12 . 9905 and the deviation of peak time of computed and observed outflows (DPOT) ¼ 0 j the sum of the absolute value of the deviations betweeen computed and observed outflows (SAD) ¼ 1835 .