Simulation of Runoff and sediment Yield in Haraz River Basin in Mazandaran using SWAT model

Simulations of rivers flow and better understanding of different components of hydrologic cycle are Important in order to programing the conservation aspects of water resources. Since the study area is located in the site of dam construction، and in order to better management of water resources، the estimation of rainfall runoff and sediment yield are very important. Therefore، in this study، the SWAT model was applied. SWAT model is one of the Multippurpose simulation models for management of the watershed. The main objective of hydrologic models is the simulation and prediction of the behavior of the catchment basin of the effect of the variable on the watershed system. Hydrologic models to simulate land surface hydrological processes are to improve water resources management. Today، GIS tools are commonly used in natural resource management; especially in watersheds with the several banks are linked information such as digital maps. GIS to predict the results of management activities designed and developed. For situation awareness systems، we need to add the elements of system dynamics. SWAT model is an advanced communication window، possible to combine a set of models and GIS data in groundwater and surface water flows and flood flows are provided. Study area between 539،022 to 622،236 Eastern longitude and 3،923،033 to 4،009،208 north latitude is located. Haraz watershed with an area of 328527/2 hectares is located to the south of the province and the Amole city. The minimum height of 300 meters and a maximum height of 5600 meters is the area. Calculating runoff in SWAT model Simulated runoff by SWAT model can be done in two ways: Grien Amped and SCS curve. SWAT model to simulate the hydrological cycle on the water balance equation is based. SWt=SWo+∑_ (i=1) ^t▒ (R_day-Q_surf-Ea-w_seep-Q_gw) Predict the rate of soil erosion caused by rainfall and runoff in SWAT model is based on equation MUSLE. In this method، surface runoff is used as an agent of erosion. Sediment transport lag in the effect of snow cover on erosion، sediment and groundwater lateral flow is also calculated. In order to improve the quality of model calibration and uncertainty analysis in SWAT-CAP software sufi2 method was used. SUFI2 program combined calibration uncertainty and tries to determine parameter uncertainty، so that most of the observed data in the region of uncertainty can be determined. Using ARC- SWAT software watershed study area was divided into 25 sub basin. Because of the diversity of land use map and soil the sub basins was divided in 91 hydrologic units (HRU). In the following the calibration and validation، during the first stage 20 variables were selected and the initial values are based on a list prepared by the guide table SWAT، the application entered SWAT CUP. After 600 iterations each algorithm separately SUFI2، 8 parameters for simulating runoff and sediment load parameter 5 as sensitive parameters were determined. Then model was calibrated to simulate runoff for years of 1995-2004، and evaluated using correlation coefficient (R2)، coefficient of Nash – Sutcliffe (NS) and Mean of Squared Error (MSE). The results showed that the values of mentioned coefficients in the Karehsang station are 0. 80، 0. 77، and 20. 93، in Chelav Station is 0. 75، 0. 73، and 1. 23; in Razan Station is 0. 80، 0. 79، and 5. 91 and in Panjab station are 0. 68، 0. 55، and 2. 7 respectively. Also sediment yield was calibrated in Karehsang station for years of 2002-2006 and statistical coefficients (R2) and NS obtained by 61 and 60 percent، respectively. In order to validation، the model was run for years of 2005-2009. Results showed that mentioned coefficients are 0. 87، 0. 75، 10. 17 for Karehsang station; 0. 83، 0. 77، 0. 88 for Chelav station; 0. 81، 0. 72، 1. 34 for Razan station، and 0. 75، 0. 70، 0. 17 for Panjab stations. Validation of sediment yield was done for years of 2007-2008 with coefficients of NS and R2 equal to 53 and 68 percent. The primary objective of this study was to evaluate the performance of SWAT model in simulating runoff and sediment yield Haraz watershed gauging stations within the basin. In the sensitivity analysis of various parameters for runoff curve number (CN)، base flow alpha factor for reserve side (ALPHA-BNK) and hydraulic conductivity effects (CH-K2) are of high sensitivity. The high sensitivity of the CN parameter in the domain studied the role of environmental factors and land use on runoff areas is studied. The results of the study whit results of studies Panagopoulos and colleagues (2011) and Parajuli and et al (2013) are consistent. For predicting sediment Parameters for the simulation of sediment load SPCON، SPEXP and SOL_AWC is more sensitive. According to the figures، the values of peak runoff and soil loss estimates are close to the observed value. Finally، results indicated that model has a high level of performance in simulation flow discharge and sediment yield simulation، and it can be used in order to operating watershed management strategies.