Efficiency of Time- Area and Clark instantaneous unit hydrograph models in estimating flood discharge

One of the main objectives of hydrology is rainfall–runoff forecasting process for determination of flood hydrograph at the outlet of a watershed. The aim of this study was to investigate the consistency، accuracy and reliability of time–area and Clark instantaneous unit hydrograph models for estimating the shape، peak discharge، time to peak، base time and volume of flood resulting from a rainfall with certain intensity and duration. For this purpose، the topographic map of Bazoft watershed was digitized by using R2V package، the digital elevation model (DEM) and isochronal prepared with the ILWIS software. Finally، the flood hydrographs were estimated by Clark and time-area models for six selected storm events. The computed hydrographs then compared with those obtained by measured data an outlet of the basin. The results showed that while both methods have some errors، the Clark model gives a better estimation of outlet hydrograph in comparison with time-area model. The amount of relative error for peak discharge for Clark and Time- Area methods were 23. 3% and 32. 8%، respectively.