Prediction of geomorphologic parameters of catchment without GIS to estimate runoff using GIUH model

Abstract. Estimation of flood in ungauged catchments has great importance in the design of hydraulic structures. The geomorphologic instantaneous unit hydrograph (GIUH) technique uses geomorphologic parameters to estimate catchment runoff. In this research, regression equations were developed based on geometrical characteristics of nine catchments such as area, length and slope of the main river to estimate geomorphologic data of other catchments with no need for GIS and digital elevation model. These equations were used for verification of stream-order-law ratios as well as geomorphologic parameters corresponding to the Gagas, Heng-Chi and Kasilain catchments. In this study, the effect of stream-order-law ratios on the rate of runoff in Kasilian catchment was examined, and the sensitivity of each ratio was analyzed. The GIUH model was assessed in two cases of GIS-supported and GIS-unsupported. The mean errors of the regression equations in estimation of ratios R_B, R_L, R_A, R_S and R_SO in three study catchments were 4.7 %, 23.5 %, 7.1 %, 41.3 %, and 22.9 %, respectively. The direct runoff hydrograph for the Heng-Chi and the Kasilian catchments were computed by GIUH model and compared with observed runoff. According to the results, the errors of peak discharge for four rainfall-runoff events in GIS-unsupported case were, on average, 10 % more than the error in the case of GIS-supported GIUH. The results of GIUH for the two cases are very close to each other. The mean coefficient of efficiency of the model was computed as 0.87.