Hydrological modeling of Amaravila watershed in neyyar river basin using soil and water assessment tool (SWAT)

A hydrological model was developed using Soil and Water Assessment Tool (SWAT) for runoff estimation in Amaravila watershed of Neyyar river basin in the state of Kerala. 19 years (1991–2009) runoff data was used for the study in which 9 year (1991–1999) data was employed to develop and calibrate the model. However, 10 years monthly data (2000–2009) was used for the evaluation purpose. The entire watershed area was divided into five sub-basins comprising 142 hydrological response units through SWAT. Sensitivity analysis of SWAT model indicated most sensitive parameters influencing runoff are curve number (CN), soil evaporation compensation factor (ESCO), available water capacity of the soil layer (SOL_AWC) and threshold depth of water in the shallow aquifer to cause revamp (REVAPMN). Performance evaluation indicators were coefficient of determination (R²), Pearson correlation coefficient (r), Nash-Sutcliff efficiency (ENS) and root mean square error (RMSE). These were 0.89, 0.88, 0.72 and 0.14 respectively for calibration and 0.83, 0.88, 0.77 and 0.17, respectively for evaluation purpose. Water balance indicated that about 58 percent of rainfall flows out of the basin as surface runoff. It was observed that average annual groundwater flow is 2% of average annual rainfall and the annual evapotranspiration is 38% of the average annual rainfall in the watershed.