Comparison of unit hydrograph and Grey theory in flood hydrograph estimation (Case study: Shahrchay Watershed, Urmia, Iran)

The study and analysis of non-linear rainfall - runoff procedure to model and determine the different components of the flood hydrograph, including peak flow- the volume of runoff and etc. has long been of interest to hydrologists. In this study, two methods of unit hydrograph and Gary theory were analyzed to estimate flood hydrograph for Shahrchay basin located in West Azerbaijan. For this purpose, several flood hydrograph and precipitation observation data was used to model the mentioned basin. Based on observational data, the parameters of both the unit hydrograph and Grey models were estimated and then the developed model was used to determine the characteristics of the flood hydrograph. Evaluation and comparison of the different specifications of predicted and observed flood hydrograph showed that Grey theory compared to unit hydrograph method has more capabilities in modeling and predicting flood flow hydrograph in basin. Among them, we can note the average error in the volume of flood with values of 32 and 18 percent in the unit hydrograph method and Grey theory, respectively.