The Relationship between Physiographic Characteristics of Watershed with Runoff and Sediment Production‌ (Case Study: Selected Watersheds of Razavi Khorasan Province)

Sediment and runoff production depend on different factors and the recognition of effective factors helps significantly the issue of watershed management. The aim of this research is determination of the relation between sediment-runoff production and physiographic characteristics in 26 selected catchments in Razavi Khorasan. In this regard, after determining the catchments’ boarders, 13 physiographic characteristics, were calculated using ArcGIS9.3 software. A common hydrological data period of 20 years was considered from 1986 to 2006. Then the stations with missing data were recompleted using normal ratio method. In order to determine the correlation between physiographic characteristics and sediment-runoff factors, their correlation coefficients were obtained and in order to evaluate the relationships, the stepwise multiple regression was used using SPSS22 software and the selected models presented. Another aim of this research was to use cluster analysis as a tool to determine homogenous catchments, so that with classification, the catchments heterogeneity causing factor is determined. According to the correlation results, the most relevant characteristics in sediment production were determined as elevation, slope, main channel length, and drainage density and in runoff production were determined as shape and form factor, circularity ratio, elongation ratio and the diameter of the circle level. According to the results of the regression, the most effective characteristic in sediment production was the drainage density and in runoff production determined including the form factor, elongation ratio and shape factor, respectively. Cluster analysis was also done in 4 distinct steps based on physiographic characteristics, runoff indices, sediment indices and all the above mentioned factors. The results from cluster analysis in mentioned methods showed that using different input factors, different classification is obtained for studied catchments.