Taoufik Hermassi ^1* Fathia Jarray ^1* Waad Tlili ² Issam Achour ² Mohamed Mechergui ²

• ¹ National Research Institute for Rural Engineering, Water and Forestry (INRGREF), Ariana, Tunisia
• ² National Institute of Agronomy of Tunisia, Tunis, Tunisia

Analyzing the hydrological dynamics and assessing the impact of Soil and Water Conservation (SWC) techniques provides crucial insights for developing region-specific conservation strategies and advancing effective watershed management. This study investigates the impact of SWC measures on the hydrological dynamics of the Merguellil watershed, Central Tunisia. The research includes a sensitivity analysis, as well as the calibration and validation of the SWAT model, revealing seven sensitive parameters. During calibration (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012), NSE was 0.82 and R² was 0.9. In validation (2013-2020), NSE was 0.81 and R² remained 0.9, indicating a strong correlation. Simulating the SWAT model with and without SWC techniques reveals a consistent reduction in surface runoff, notably in central subbasins with values exceeding 15%. The observed decrease is attributed to vegetation cover, indicating the effectiveness of SWC practices. In contrast, subbasins lacking SWC interventions exhibit minimal runoff changes. The study further assesses the impact of SWC techniques on soil erosion, revealing negative percentage differences that indicate a reduction in erosion of over 30% following the implementation of these techniques. The central subbasins, marked by olive trees and strategic conservation, demonstrate substantial decreases, emphasizing successful erosion control efforts. Groundwater recharge analysis shows that SWC practices, along with favorable conditions, significantly enhance percolation and groundwater recharge, highlighting their beneficial impact. Variations in recharge percentages across subbasins reflect the nuanced responses influenced by anthropogenic and natural factors. Notably, groundwater recharge percentages increase by over 20% in treated areas compared to untreated ones. Finally, the study underscores the vital role of SWC techniques in mitigating surface runoff, reducing soil erosion, and enhancing groundwater recharge in the semi-arid Merguellil watershed. The findings emphasize the need for tailored conservation strategies considering geographical variations for effective watershed management and sustainability.