The adequacy of the SWAT model in the estimation of runoff, sediment yield and nitrate loss in the Gorganrood watershed was tested, using the existing spatial database as the primary data. The model was then executed for a 31-years’ time period. In combination with the SWAT model, the Sequential Uncertainty Fitting Program (SWAT-CUP and SUFI-2) was added used to calibrate and validate a hydrologic model of the watershed. The obtained values at 14 stations were between 0.48 to 0.83 for NS and 0.58 to 0.90 for R², respectively. The results showed that nitrate loss was higher in cultivated lands, and in the loess deposits. The maximum amounts of runoff and sediment yield were largely produced in steep areas of the watershed, where dry farming was practiced. In general, the results showed that SWAT could be a proper tool for simulating runoff, sediment yield and nitrate loss into the river.

Keywords: SWAT model, SUFI-2, runoff, Sediment, Nitrate loss

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