Document Type : Research Paper
Authors
1 Ph.D. Student of Soil Science, Department of Soil Science, Faculty of Agriculture, University of Zanjan.
2 Department of Soil Science, Faculty of Agriculture, University of Zanjan,. Zanjan, Iran.
Abstract
The concentration time of catchments is one of the most important and common effective features in hydrological studies, particularly in determining the flow discharge for designing watershed management projects. Most of the catchments in the world especially in Iran were not equipped with hydrometric stations, and project managers are forced to use traditional empirical models to estimate concentration time and peak flow. The aim of this study is to evaluate the efficiency of empirical models for estimating the concentration time in sub basins and to investigate its determining factors. The concentration time in eight sub basins from Urmia Lake and Araz River basins in Northwest Iran was calculated by examining the hydrograph of stream flows in a statistical period of 30 years (from 1367 to 1397). It was estimated through six empirical models including Kirpich (1940), Kerby (1959), Chow (1962), Federal Aviation Administration (1972), Bransby-Williams (1980) and Ventura (2007). The characteristics of the sub basins such as area, length, slope, height and shape were determined through field studies and drawing maps in GIS platform. According to the results, Shekaralichay sub basin has the shortest (66 minutes) and the Kalaleh sub basin has the longest concentration time (132 minutes). Bransby-Williams model had the lowest error (6.8 %) and the highest efficiency coefficient (73%); While the estimation error (36.2 %) and the efficiency of Federal Aviation Administration model was 36.2% and-14.4% respectively. The slope was the most important main factor on the estimation of concentration time of the assessment in the Kirpich model (r= 0.83), Chow (r= 0.82) and Bransby-Williams (r= 0.73). Considering the lower error of the Bransby-Williams model, this model has sufficient certainty in estimating the concentration time in the basins of the semi-arid region. Therefore, this model can be used in similar sub basins in terms of environmental characteristics.
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