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Aouissi J.,University of Carthage | Aouissi J.,French National Institute for Agricultural Research | Aouissi J.,Agrocampus Ouest | Benabdallah S.,Center for Water Research and Technologies | And 2 more authors.
Journal of Environmental Quality | Year: 2014

Agriculture intensification has impaired water quality. In this study, the risk of pollution by nitrates was assessed by experimental monitoring, spatial integration of farm census, and modeling of water quality using the Soil and Water Assessment Tool (SWAT), version 2009, over the period of 1990 to 2006 for a catchment located northern Tunisia. Under a semiarid climate, the water quality is influenced by the predominating agriculture activities. The hydrological results are compared with the observed flows derived from measurements at the outlet of the Joumine watershed. Model performance showed good statistical agreements, with a Nash-Sutcliffe efficiency of 0.9 and a r2 value of 0.92 after monthly calibration. The model predicted the timing of monthly peak flow values reasonably well. During the validation period, SWAT simulations were nearly as accurate, with Nash-Sutcliffe efficiency and r2 values of 0.89 and 0.92, respectively. The model was used to simulate NO3 concentrations. The predicted NO3 concentration values were compared with in situ measured concentrations. The simulated and measured NO3-N concentrations varied in the same range of 0 to 5 mg L-1 at the E3 and E5 locations. The calibrated model was then used for simulating the impact of the best management practice scenarios to reduce NO3 loads to the river. The first set-up consisted of reducing the N fertilizer application by 20 and 100% from the current state. These two scenarios induced a reduction in NO3 loads by 22 and 72%, respectively. The second set-up consisted of using vegetation filter strips. The last scenario combined filter strips and a reduction of 20% in N fertilizer application. Results showed NO3 reduction rates of 20 and 36%, respectively. The SWAT model allowed managers to have several options to improve the water quality in the Joumine watershed. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Post J.,German Aerospace Center | Strunz G.,German Aerospace Center | Hummel F.,German Aerospace Center | Benabdallah S.,Center for Water Research and Technologies | And 2 more authors.
iEMSs 2012 - Managing Resources of a Limited Planet: Proceedings of the 6th Biennial Meeting of the International Environmental Modelling and Software Society | Year: 2012

The project CLIMB (Climate Induced Changes on the Hydrology of Mediterranean Basins - Reducing Uncertainty and Quantifying Risk through an Integrated Monitoring and Modelling System, www.climb-fp7.eu) aims to investigate present and future climate induced changes in the hydrological budgets and extremes for Mediterranean and neighbouring countries. We provide a concept for an integrated modelling and assessment set-up to tackle the challenge of quantifying parameter related uncertainties and associated risks with the water balance simulation model ETH (WaSiM-ETH) for the cultivation of tomatoes in Chiba basin, Tunisia, which is a test site within the CLIMB project. This study indicates that it is already delicate to cultivate tomatoes in the watershed under rain-fed conditions with a deteriorating trend in the future. This is associated with considerable yield reduction for tomatoes and thus economic impacts for local farmers.

Mosbahi M.,National Engineering School of Tunis | Benabdallah S.,Center for Water Research and Technologies | Boussema M.R.,National Engineering School of Tunis
Earth Science Informatics | Year: 2015

Water resource and hydrologic modeling studies are intrinsically related to spatial processes of hydrologic cycle. Due to generally sparse data, and high rainfall variability, the accurate prediction of water availability in complex semi-arid catchment depends to a great extent on how well spatial input data describe realistically the relevant characteristics. The Geographic Information System (GIS) provides the framework within which spatially distributed data are collected and used to prepare model input files. Despite significant recent developments in distributed hydrologic modeling, the over-parameterization is usually a critical issue that can complicate calibration process. Sensitivity analysis methods reducing the number of parameters to be adjusted during calibration are important for simplifying the use of these models. The objective of this paper is to perform a sensitivity analysis for flow in a semi-arid catchment (1,491 km2), located in northwestern of Tunisia, using the Soil and Water Assessment Tool (SWAT) model. The simulation results revealed that among eight selected parameters, curve number (CN2), soil evaporation compensation factor (ESCO), soil available water capacity (SOL_AWC) and threshold depth of water in the shallow aquifer required for return flow (GWQMN) were found to be the most sensitive parameters. Calibration of hydrology, facilitated by the sensitivity analysis, was performed for the period 2001 through 2003. Results of calibration showed that the model accurately predict runoff and performed well with a monthly Nash Sutcliffe efficiency (NSE) of 0,78, a coefficient of determination (R2) of 0,85 and a percent of bias (PBIAS) equal to −13,22 %. © 2014, Springer-Verlag Berlin Heidelberg.

Aouissi J.,University of Carthage | Chabaane Z.L.,University of Carthage | Benabdallah S.,Center for Water Research and Technologies | Cudennec C.,Agrocampus Ouest
IAHS-AISH Proceedings and Reports | Year: 2014

The impact of changes in agricultural land use and practices as a controlling driver of hydrologic response and as a source of diffuse pollution, are studied in the Joumine River basin, discharging into the Ichkeul Lake, northern Tunisia, a UNESCO World Heritage site since 1979. The lake is characterized by a very specific hydrological functioning based on a seasonal alternation of water levels and salinity through its link to the Mediterranean Sea. Three Landsat images, in situ surveys and SWAT modelling were used to simulate and assess streamflows and nitrate loads under retrospective land uses. © 2014 IAHS Press.

Mosbahi M.,National Engineering School of Tunis | Benabdallah S.,Center for Water Research and Technologies | Boussema M.R.,National Engineering School of Tunis
Arabian Journal of Geosciences | Year: 2013

Soil erosion is one of the most serious land degradation problems and the primary environmental issue in Mediterranean regions. Estimation of soil erosion loss in these regions is often difficult due to the complex interplay of many factors such as climate, land uses, topography, and human activities. The purpose of this study is to apply the Soil and Water Assessment Tool (SWAT) model to predict surface runoff generation patterns and soil erosion hazard and to prioritize most degraded sub-catchment in order to adopt the appropriate management intervention. The study area is the Sarrath river catchment (1,491 km2), north of Tunisia. Based on the estimated soil loss rates, the catchment was divided into four priority categories for conservation intervention. Results showed that a larger part of the watershed (90 %) fell under low and moderate soil erosion risk and only 10 % of the watershed was vulnerable to soil erosion with an estimated sediment loss exceeding 10 t ha-1 year-1. Results indicated that spatial differences in erosion rates within the Sarrath catchment are mainly caused by differences in land cover type and gradient slope. Application of the SWAT model demonstrated that the model provides a useful tool to predict surface runoff and soil erosion hazard and can successfully be used for prioritization of vulnerable areas over semi-arid catchments. © 2012 Saudi Society for Geosciences.

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