Changeability of simulated hydrograph from a steep watershed resulted from applying Clark’s IUH and different time–area histograms

Abstract

Reflecting the shape and drainage characteristics of the watershed, time–area histogram (TAH) seems to be the most important parameter for derivation of the transformation hydrograph. In this study, a semi-distributed instantaneous unit hydrograph was established and applied to the steep 103 km2-Galazchai watershed in Iran to improve the results of the rainfall–runoff modelling. Towards this attempt, twenty-three runoff producing events with wide different characteristics were used for the analysis. The direct surface runoff hydrographs (DSRHs) were obtained and consequently compared for the study area using Clark’s instantaneous unit hydrograph (IUH) and through applying different TAHs calculated based on channel profile, dimensionless TAH, average velocity and spatially distributed travel time methods. A weight grid developed from kinematic wave travel time equation for overland flow was prepared and used as input to derive the spatial TAH of the watershed. The results indicated that the different TAHs had noticeable impacts on the estimated hydrographs. The results also proved that the spatial TAH method performed well with efficiency criteria of 0.75 and 0.69 in calibration and validation steps. The implemented method also offered the advantages of flexibility, efficiency and physically powerful links to the spatial data set and GIS software.