Shahid Chamran University of AhvazIrrigation Sciences and Engineering2588-595243120200320Comparison of Different Methods Efficiency for Estimation of Nash Instantaneous Unit Hydrograph Parameters in Flood Simulation (Case Study: Aland-Chay, Gara-Chay, Mahabad-Chay and Zab Rivers)Comparison of Different Methods Efficiency for Estimation of Nash Instantaneous Unit Hydrograph Parameters in Flood Simulation (Case Study: Aland-Chay, Gara-Chay, Mahabad-Chay and Zab Rivers)15281557310.22055/jise.2017.18316.1330FANeda KhanmohammadiPh.D. in Water Resources Engineering, Urmia University, Iran.Javad BehmaneshProfessor, Department of Water Engineering, Urmia University, Iran.Journal Article20160620The Unit Hydrographic Theory, which was first proposed by Sherman in 1932, is used as one of the most important rainfall-runoff methods in hydrology. One of the most efficient models in simulating rainfall-runoff phenomenon is the conceptual model known as Nash Instantaneous Unit Hydrograph. In this model, the number of reservoirs and storage coefficients describes the complete shape of Instantaneous Unit Hydrograph (Ahmadin et al., 2010). <br />The model consists of two parameters including n and k. Different methods have been presented to estimate the mentioned parameters. Inaccurate estimation of the model parameters (n and k) causes an error in simulated hydrograph. Methods such as the moments, the least square and the maximum likelihood are some of the proposed ones (Snyder, 1955; Eagleson et al., 1966). The large number of parameters of these methods has limited their use (Rao and Tirtotjondro, 1995). Thus, the researchers tried to develop a model with lower number of parameters and more acceptable accuracy. <br />Some researchers such as Aron and White (1982), Collins (1983), Rosso (1984), Hann et al. (1994), Singh (1998), Singh (2000), Singh et al. (2007), and Bhunya et al. (2003) proposed relationships for estimating Nash Model’s parameters. Others, including Bahremand and Mostafazadeh (2010), Ahmadin et al. (2010) and Aslani et al. (2016) used the proposed relationships and estimated the parameters of Nash model in three different basins of Iran.The Unit Hydrographic Theory, which was first proposed by Sherman in 1932, is used as one of the most important rainfall-runoff methods in hydrology. One of the most efficient models in simulating rainfall-runoff phenomenon is the conceptual model known as Nash Instantaneous Unit Hydrograph. In this model, the number of reservoirs and storage coefficients describes the complete shape of Instantaneous Unit Hydrograph (Ahmadin et al., 2010). <br />The model consists of two parameters including n and k. Different methods have been presented to estimate the mentioned parameters. Inaccurate estimation of the model parameters (n and k) causes an error in simulated hydrograph. Methods such as the moments, the least square and the maximum likelihood are some of the proposed ones (Snyder, 1955; Eagleson et al., 1966). The large number of parameters of these methods has limited their use (Rao and Tirtotjondro, 1995). Thus, the researchers tried to develop a model with lower number of parameters and more acceptable accuracy. <br />Some researchers such as Aron and White (1982), Collins (1983), Rosso (1984), Hann et al. (1994), Singh (1998), Singh (2000), Singh et al. (2007), and Bhunya et al. (2003) proposed relationships for estimating Nash Model’s parameters. Others, including Bahremand and Mostafazadeh (2010), Ahmadin et al. (2010) and Aslani et al. (2016) used the proposed relationships and estimated the parameters of Nash model in three different basins of Iran.https://jise.scu.ac.ir/article_15573_1cb8833cf70ca6f2e5093951a2403965.pdf