Estimation of stream-order-ratios of catchments without GIS for modeling of catchment's runoff using the GIUH method

The GIUH method is one method which deals with prediction of the catchment’s runoff based on the stream-order-ratios (SOR) data and the geomorphologic data of the catchments lacking statistics. Many of the catchments, lack digital DEM map and need GIS to provide them which requires GIS expertise and spending extra time in which may of the hydrologists are not interested and are looking for simpler runoff-rainfall models. In this study, based on the stream ordering data of nine different stream catchments in the world some equations have been provided to determine stream-orderratios. Five regression equations have been presented to measure the geomorphologic of the streams including bifurcation ratio (RB), length ratio, area ration(Ra), (RL), stream slope ratio (RS) and overland slope ratio (RSO). The results of SOR for three other catchments have been evaluated. Based on the regression equations, the surface runoff of the other catchments of Heng-Chi and Kasilian using the GIUH method were estimated. Based on the results, the peak error of the calculated runoff using GIUH model based on the regression equations was 10% more than the model’s measurements based on the real data obtained from GIS. The errors of the model in the estimation of RB, RL, RA, RS, and RSO in the three case study catchments were 4.7%, 23.5%, 7.1%. 41.3%, and 22.9%, respectively. The relative sensitivities of the ratios RB, RL, RA, RS, and RSO are shown to be 0.56, 0.01, 0.92, 0.042, and 1.33, respectively.