|Title:||Improving the Applicability of the SWAT model to simulate flow and nitrate dynamics in a flat data-scarce agricultural region in the Mediterranean |
|Authors:||Donmez, C., O. Sari, S. Berberoglu, A. Cilek, O. Satir and M. Volk |
|Volume (Issue):||12(12) |
|Article ID:|| |
|URL (non-DOI journals):|| |
|Broad Application Category:||data or component development |
|Primary Application Category:||GIS interface, GIS utility, or other type of interface/utility |
|Secondary Application Category:||nitrogen cycling/loss and transport |
|Watershed Description:||2132 km^2 Lower Seyhan Plain (LSP), which is located along the eastern Mediterranean coast of Turkey and is characterized by elevations ranging from 0 to 23 m. Around 81% of the entire basin area is irrigated. Open irrigation systems and drainage infrastructures are managed by the State Hydraulic Works (DSI) of Turkey. Mediterranean climate dominates the region with an annual total of 730 mm precipitation and a mean annual temperature of 30 ℃ for summer and 7 ℃ for winter. Due to the privileged climate and fertile soils, LSP is one of Turkey’s most productive agricultural areas, providing approximately 10% of the total agricultural production. Large-scale irrigated agriculture extends throughout the lower delta, where maize, citrus fruit, cotton, wheat, and vegetables are cultivated and exported to the European Union, Russia, and other neighboring countries. These crops depend on water provision supplied by reservoirs that store the runoff of winter, rain, and snow in the upper mountainous areas.
The Seyhan Dam supplies irrigation water to the LSP through a two-conveyance canal and the Seyhan River. The flow downstream of the diversion dam is used as one of the main sources for irrigation and is deficient. This water deficiency will be increased according to the rising demand to maintain the river ecosystem in the future . Besides, the impacts of fertilizer load on salinity, water pollution, and other environmental issues are still unclear, especially on the Ramsar wetlands, including Akyatan and Agyatan Lagoons of Cukurova Delta along the coastal belt of LSP. A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention. Thus, the LSP represents an ideal testbed for examining the capability of the SWAT model to simulate hydrology and water quality in such a complex agricultural plain. Figure 1 shows both the location of the LSP and the gauging stations used in the study.
There are four main discharges of the drainage networks of the LSP (three to the Mediterranean Ocean, one to Akyatan Lagoon). We set up four real-time stream gauging stations (funded by the Turkish Scientific and Research Council (TUBITAK), Project No: 115Y063) at these locations to accurately measure the accumulated drainage flow from the entire study region. Each station included a Limnigraph and a multi-parameter device that measured Electrical Conductivity (EC), temperature, Total Dissolved Soils (TDS), Turbidity, Dissolved Oxygen, pH, and Nitrate on an hourly basis. A data logger on the station transferred the measured data to the server in our Remote Sensing and Geographic Information System laboratory at Cukurova University via data modem and General Packet Radio Service (GPRS). A separate concrete and steel construction platform was built for the Yemisli station (at Akyatan Lagoon) to cover all of the water inlets to the lagoon, while other stations were built on fixed structures such as bridges. The water level is measured by the radar system instead of a limnigraph at Bebeli station since the drainage channel in this area consists of mud after 2–3 m depth; this increased the station cost. |
|Calibration Summary:|| |
|Validation Summary:|| |
|General Comments:|| |
|Abstract:||Understanding the soil and hydrologic processes in agricultural watersheds are vital for reliable assessments of water quantity and quality to support integrated river basin management. However, deriving hydrology-relevant information is complicated in flat data-scarce agricultural watersheds due to constraints in watershed delineation, flat topography, poor natural drainage, and irregular irrigation schedules by human intervention. The study aimed to improve the applicability of the Soil and Water Assessment Tool (SWAT) model to simulate daily flow and NO3 concentrations in a flat data-scarce agricultural watershed in the Lower Seyhan Plain (LSP) in Turkey. Refined digitized stream networks, discharge data derived from fully equipped gauging stations, and satellite data (Landsat 7 ETM+, Aster GDEM, etc.) had to be integrated into the modeling process to improve the simulation quality. The model was calibrated using a 2-year (2011–2012) dataset of streamflow and NO3 using the Sequential Uncertainty Fitting (SUFI-2) approach and validated from 2013 to 2018. Daily water yields were predicted with a reasonable simulation accuracy (E values ranging from 0.53 to 0.82 and percent bias (PBIAS) from 0 to +4.1). The results proved that integrating redefined stream networks to SWAT within a Geographic Information System (GIS) environment increases the simulation capability of flow and nitrate dynamics efficiently. Automated delineation of these networks and sub-basins at low topographic transitions limits the SWAT accuracy. |
|Keywords:||SWAT; SUFI-2; daily flow; NO3; Lower Seyhan Plain; data-scarce regions; Mediterranean |