A GIS-Independent method for Stream-Order-Law Ratios Prediction in Catchments for Runoff Estimation

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Aim of the study(1) present equations that can predict the stream-order-law ratios on the basis of length, slope of the stream and area of the catchment; (2) apply predicted stream-order-law ratios to estimate direct runoff of catchments by GIUH method.Material and methodsIn order to use GIUH model, the stream network’s characteristics, such as bifurcation ratio (RB), stream-length ratio (RL), stream-area ratio (RA), stream-slope ratio (RS) and overland slope ratio (RSO) must be evaluated. For this purpose, accurate GIS based information of topography and hydrography is often necessary, but in many catchments such information could lack. In this study, equations have been presented that are related to geometrical information of the catchment, such as area, slope and length of the main river, which are available. The presented equations have been developed based on non-linear regressions of data from nine catchments.Results and conclusionsTo validate the proposed method, the data of three other catchments were used. Based on the presented equations, the runoff of Heng-Chi (Taiwan) and Kasilian (Iran) catchments was calculated by GIUH method. Based on the results, the peak runoff error calculated by GIUH model based on regression equations was 10% higher than model calculations based on data obtained from GIS. The average error of the regression equations in estimating the coefficients of RB, RL, RA, and RS in the three case study catchments are 4.7%, 23.5%, 7.1%, 41.3% and 22.9%, respectively. The relative sensitivity coefficient of RB, RL, RA, and RS ratios on peak flow was observed as 0.56, 0.01, 0.92, 0.042, and 1.33 respectively.