Dept. of Watershed Management, Science and Research Branch , Islamic Azad university, Tehran, Iran
With regard to the importance of instantaneous peak discharge estimation for watershed management study, and due to the lack of and unqualified climatic and hydrologic data for estimation and measurement in countries such as Iran, researchers were obliged to establish a link between constant parameters (geomorphologic) and variables (hydrologic) to present models with minimum dependence on climatic and hydrologic data in hydrologic estimations. This research has made an effort to use synthetic unit hydrographs at the drainage basin of Kan (Soleghan River) and to compare these results with recorded peak discharge at the watershed outlet, in order to derive the best model. Comparison of study models using relative mean error (RME) and root of mean square error (RMSE) in the study drainage basin located in central Alborz watershed showed that RME for the Geomorphologic model was 17.99 and RMSE was 15.49, for Snyder RME was 59.66, and RMSE was 29.83, for SCS RME was 162.63 and RMSE was 76.002 and finally triangular RME was 165.82 and RMSE was 77.44. Therefore the best estimation belonged to the Geomorphologic model followed by the Snyder, SCS and Triangular models. Owing to the lack of recorded instantaneous peak discharges in the hydrometric station of the Kan drainage basin (11 events) at Kan-Soleghan, we are not able to derive an instantaneous peak discharge model. Hence by using factors in each of the studied models, other effective factors and 283 recorded events of daily peak discharges, the daily peak discharge model can be derived.