Adaptation and Evaluation of SWAT Model for Application in an Arid Watershed in southeast Tunisia

Abstract

In the arid regions of Tunisia, huge efforts are being made in water harvesting and soil conservation. A growing need for the assessment of their impact is felt. Due to the complexity of the processes at the watershed level, recourse to modeling is inevitable. In this framework, the objective of this paper is to adapt and evaluate the ArcView SWAT model for application in the assessment of the hydrological impact of water harvesting works. Some adjustments were made to the SWAT code to adapt the model to the processes in this arid environment. The model was calibrated and validated using 34 daily runoff events for the Oum-Zessar watershed upstream of Koutine (270-km2). Evaluation of the hydrologic goodness-of-fit of the model based on the observed and simulated daily runoff data gave reasonable results . The model efficiency (Nash-Sutcliffe coefficient) was 0.26 for the calibration period (1975-1979) and 0.83 (1980-1992) for the validation period. The evaluation was affected by uncertainties in the data and poor rain gauge coverage and further study is needed. Watershed modeling is a time-consuming task, even more so because of the scarcity of data. Nevertheless, the model is very attractive for application, considering the gradual generalization and widening of the scope of the use of digital data layers and spatial decision support systems by the various end users (agriculture, environment, planning, etc.).