Hydrological simulation of a rainfed agricultural watershed using the soil and water assessment tool (SWAT)

Abstract

The hydrology component of the soil and water assessment tool (SWAT) watershed model was evaluated in the El-Dabaa and El-Alamian watershed of Egypt; using the runoff measured at the outlet of the watershed. At present, prediction of stream flow simulation in data-sparse basins of the northwestern coast of Egypt is a challenging task due to the absence of reliable ground-based rainfall information, while satellite-based rainfall estimates are immensely useful to improve our understanding of spatio-temporal variation of rainfall, particularly for data-sparse basins. The main objective of this chapter was to test the performance and feasibility of the SWAT model and the Tropical Rainfall Measuring Mission (TRMM) for prediction of runoff in the watershed with application to a study area in the Northwestern coastal zone of Egypt. The SWAT model requires the following data: digital elevation model (DEM), land use, soil, and daily climate data for driving the model, and runoff data for calibrating the model. All these data were collected from local organizations except DEM. All input files for the model were organized and assembled following the guidelines of ArcSWAT interface of the SWAT 2012 version. The study area was delineated into 71 sub-basins and 145 hydrological response units (HRU), which are unique combinations of land use, soil type, and slope. The model was calibrated for the period 1979–2014 and validated in the period 1971–2000 based on the availability of coinciding climatic data. The weather generator tool of the SWAT was used to fill in the missing climatic data and enabled flow simulation in the periods with missing data. The studied basins have actual runoff (Q) ranges between 0.70 and 72.9 mm annually. The study area has runoff coefficient range between 0.9 and 52% of its rainfall. Hence, the remaining rainfall is lost by infiltration and evaporation processes. Acceptable statistical parameters were obtained after calibration processes as indicated by R2 = 0.91, E = 0.78, and E′ = 0.61 for calibration and R2 = 0.82, E = 0.81, and E′ = 0.61 for validation. Considering the good results of SWAT in this study and comprehensiveness of the model in land surface processes representation, the model is very promising for runoff, land and water management studies and expected to give valuable information to resources managers.