FACT
A software package called Fast Automatic Calibration Tool (FACT) was developed for SWAT to increase the calibration performance (Özdemir and Leloglu 2018). The optimization method applied to the FACT is the Sequential Uncertainty Conformity Algorithm (SUFI-2) since a large number of parameters in conjunction with uncertainty analysis can be performed by this algorithm. The FACT was developed to reduce some drawbacks of SUFI2 in SWAT-CUP which are the time consumption, user interaction requirement, and update problems of SWAT model files (Özdemir and Leloglu 2018). The FACT was applied by using 16 important parameters that reflect relevant processes of the system such as surface runoff, baseflow, lateral flow (Table 1). The stream gauge station on the Namazgah river was used to compare observed and measured flow rates. Since the observed flow rate values at the station were between 1991 and 2007, the model was performed between these years. The station has stayed under dam waters since 2007, so no measurements are available.

Data preparation

The data prepared for the model are divided into two different types, time series and spatial inputs. The hydrologic cycle of the basin is simulated in daily and monthly time steps by the model. Meteorological data sets, minimum and maximum temperatures, rainfall, average relative humidity, average wind speed, average solar radiation, are used as time series type inputs whereas land use and soil layers are spatial data type inputs. Daily time steps were used in this study.

The Digital Elevation Model

The Digital Elevation Model (DEM) of the Namazgah dam basin was produced from 1:25 000 scale topographic maps. The resolution of DEM is 30*30 meters. Universal Transverse Mercator (UTM) projection system and WGS_1984_35 N geographic coordinate were used in DEM. SWAT calculated minimum, maximum, mean and standard deviation elevation values which were 40, 350, 165.437 and 53.72, respectively. After preprocessing of DEM, minimum, maximum, and suggested sub-basin areas were calculated as 52, 10340, and 1000 in hectares, respectively. Based on streams and animal husbandry locations in the basin, 50 sub-basins outlets were defined (Fig. 1).

Soil map

SWAT model calculates hydrological processes in the basin using the physical and chemical properties of the soil. The most important of these features are; soil water availability capacity, hydraulic conductivity, organic carbon content, soil texture (sand, clay and gravel content) and thickness. Unfortunately, the soil map produced by the former Ministry of Food, Agriculture and Livestock (Oakes 1958) does not include these properties. It only includes Great Soil Groups and combination of soil properties, slope-depth, drainage-texture, drainage-salt-alkali combinations. The legend of the map is presented in the following: