Investigation of performance of instantaneous unit sediment graph (IUSG) in predicting flood events sediment graph of flood events of Gharachay River

Instantaneous unit sediment graph (IUSG) is one of the methods for predicting sediment graph of the flood events and its application needs to estimation of storage coefficient (Ks)، dimensionless shape factor (ns)، time to peak (tp) and instantaneous sediment supply. Investigation of relationships among the mentioned parameters and rainfall and water discharge characteristics could facilitates use of IUSG in ungaged drainage basins. In this research concurrent flow and sediment discharge of five flood events in Poledouab hydrometric station monitored hourly. IUSG parameters calculated using observed sediment graphs and rainfall hyetographs and their relationship investigated with excess rainfall and peak water discharge of flood events. The results show that correlation coefficient (r2) of power regression equation between Ks and rainfall excess is greater than peak flow (0. /79 and 0. /42). dimensionless shape factor of ns shows statistically weak relationship with rainfall excess and peak flow but its ratio to time to peak of sediment graph (ns/tp) resulted in statistically meaningful relationship with the rainfall excess and peak flow (respectively 0. /85 and 0. /67 of r2). application of the obtained equations in this research for predicting sediment graph of some flood hydrographs and comparing the results with the sediment rating curve methods show that rising limb of the sediment graph could be predicted more accurately than falling limb of sediment graph.