Journal of Watershed Management Research

A flow-duration curve (FDC) illustrates the relationship between the frequency and magnitude of daily, weekly and monthly stream flow. Applications of FDC are of interest for many hydrological problems related to hydropower generation, river and reservoir sedimentation, water quality assessment, water-use assessment, water allocation and habitat suitability. This study was carried out in 33 selected watersheds for regional analysis of FDC in Namak Lake basin. The FDCs were drawn for 33 selected watersheds, discharges of two to 92 percent were determined and the best probability distribution was recognized among ten probability distributions. The discharges of two to 92 percent with two-year return period were estimated. Using factor analysis selected six factors, includes area, average height, main channel length, drainage density, and percentage of permeable formations among 18 physiographical, meteorological, geological and land use characteristics as independent variables for regional of analysis of FDC. The multiple regression technique and combination of cluster analysis for determination of the homogenous watersheds and multiple regression techniques were carried out regional analysis of FDC. Determination coefficient (R²), root mean square error (RMSE) and efficiency coefficient (CE) statistics are employed to evaluate the performance of the models in all region and homogeneous regions. The results showed that regional analysis with homogeneous regions causes higher efficiency and lower error. According to beta coefficient of the regression equations, the continuity of the main channel flow rate was the most important parameter in the FDC.