Abstract

Having an overall picture of the intensity of erosion and sediment yield in the watersheds of a country is an essential planning criterion for its land and water management. In this study ten suitably distributed hydrometric and sediment stations with availability of enough data were selected and the factors affecting sediment yield were measured to develop a suitable method for estimation of suspended load in sub watersheds of Nekarood and Gorgan Bay, in northern part of Iran. Twenty year average suspended load was calculated using sediment rating curve method. Multiple regressions were carried out using step by step method and by considering sediment load as dependent variable and characteristics of the watershed as independent variables. A total of 104 variables were used in simple linear, second degree and transformed equations. Among them, percentage of Pre-Quartner erosion–sensitive formations (R² = 0.996), Gravilius coefficient (R² = 0.997), percentage of land use as rangeland and dry land farming use (R² = 0.997), percentage of land as intensive and semi-intensive forests (R² = 0.993), and mean annual discharge rate (R² = 0.610), were effective on suspended sediment yield. Each of these factors describes over 99% of the suspended sediment yield variations in the equations.

Key words: Suspended load, multiple regression, watersheds of Nekarood, Gorgan Bay.