Determination of surface flow with SWAT model: A case study in the Akarsu Irrigation District

This study was conducted in the Lower Seyhan Plain located in the Çukurova Region of southern Turkey. In the study, SWAT (Soil and Water Assessment Tool) -a semi-distributed hydrological model- was applied to an agricultural catchment of 10 487 ha area including Akarsu Water User Association command area. The primary objectives of this research were: (1) to integrate the daily drainage flow data which was obtained from the flow gauging stations in the catchment into the SWAT model, (2) to simulate surface flow rates at the outlet of the agricultural catchment, and (3) to verify if the SWAT model might be applicable to the irrigated agricultural catchments. Flow and meteorological data observed from 2008 to 2014 was used in the study. Data related to the soil series and their properties, land use types, climate, land management practices, digital elevation model and man-made drainage network were used as the main material in the model domain. SUFI-2 parameter optimization algorithm in the SWAT-CUP program was employed for the calibration of the SWAT model. Model calibration and validation was done by evaluating model performance statistics of determination coefficient (R2), Nash-Sutcliffe model efficiency coefficient (NSE), and percent bias statistics (PBIAS) which measures the average tendency of the simulated data to be larger or smaller than their observed counterparts. Based on the model evaluation statistics, it was concluded that the coherence between observed and simulated values were good enough for acceptability of the SWAT model outputs, that model simulations were proven to be acceptable. Then, the calibrated and validated model was employed for estimating surface runoff, subsurface flow and base flow components in ungauged sub-catchments in the study area.