SWAT 2022 conference Prague, Praha, Czech Republic, 13 - 15 July 2022, pp.1
Many previous studies successfully applied the Soil and Water Assessment Tool (SWAT) model to mountainous areas. However, the performance of the model is still an important
research question in flat areas. This study aimed to evaluate the performance of the SWAT model in a flat agricultural plain to estimate the impacts of agricultural land use activities on water quality and quantity. Lower Seyhan Plain (LSP) is located in a downstream alluvial plain bounded by the Taurus Mountains in the north at the Eastern Mediterranean Part of Turkey where various crop schemes, including corn, wheat, cotton, soybean and citrus, are cultivated. The SWAT was run to model discharge and nitrogen potential of four gauged subcatchments in the LSP from 2015 to 2020, relying on remote sensing and in-situ inputs. It was calibrated for two years (2015-2016) and validated (2017-2020) using discharge measurements derived from four well-equipped gauging stations. Calibration efficiencies were examined by utilizing in-situ data from those stations to assess the response of the model to multi-site processes based on the Sequential Uncertainty Fitting procedure (SUFI-2). 41 relevant parameters for runoff and 15 parameters for nitrogen were determined using sensitivity analysis for the subcatchments. Results showed that the model performed well between 0.60 to 0.90 Nash-Sutcliffe Efficiency for flow while validation for nitrogen varied from 0.50 to 0.90. The multi-site validation revealed good agreement between predictions and observations; therefore, the SWAT approach captured the complex interactions between agricultural activities and hydrologic processes in a flat basin. In this case, the modelling framework presented in this study is the basis for future studies, which will address model response to irrigation schedules and agricultural trade-offs between the regional water resources in flat plains.