Effect of Time-Area Percent Curves in Development of Clark Model Unit Hydrograph

Divisional Irrigation Engineer IESL, Part I, II & III, AMIE (SL), MTech. (Water Resources), Dip. Irrig. Eng (ITIG) Director General of Irrigation BSc.Eng (Hons)(Peradeniya), C.Eng, MIE (SL), MSc (Hydraulics)(Delft) Director of Irrigation (Assets Management) BSc. Eng (Hons)(Peradeniya), C.Eng, MIE (SL) This paper describes the effect of time – area percent curves in the development of Clark model unit hydrograph. This hydrology modelling study refers to event base modeling in order to derive the unit hydrograph from Clark instantaneous unit hydrograph. For this study, Kelani river basin up to Hanwella gauging site has been represented as the study area. Hydrologic Modelling System software developed by HEC, USA (HEC-HMS) has been used for the development of unit hydrographs under the Clark UH transform model. Three numbers of different time – area percent curves of Kelani river basin have been asynchronously used as input to the Clark UH transform model in order to obtain different simulations. The parameters, time of concentration Tc and storage coefficient R values were calibrated and validated individually, against the various percent curves for the future analysis. The best suitable percent curve is identified based on the goodness of fit criteria, Nash-Sutcliffe Efficiency (NSE) with high accuracy. For the Loss model, initial and constant rate method was preferred. In the Meteorological Model, Gaged weight was considered for rainfall analysis. For the Transform Model or Direct Runoff Model, Clark UH is considered. For the Base flow model Recession, constant option was preferred. The Calibration (manual and automatic) was conducted for the storm events of May 2017, December 2014 and November 2012.Validation was conducted for the storm event of June 2014. The calibration and validation process was conducted for analyzing the hourly rainfall-runoff data for storm events observed during the monsoon seasons of the relevant years. The conclusions of the study would be very much applicable for the key personnel for taking structural and non-structural measures against the flood menace which is a frequent challenge over the study area concerned