Model setup and input data of the Sidi Salem reservoir, Tunisia

Sedimentation a major challenge to water security in arid and semi-arid regions, where reservoir operations often prioritize water retention following drought periods rather than sediment evacuation. This study investigates sedimentation dynamics in the Sidi Salem reservoir, the largest dam in Tunisia, which has already experienced an estimated 30% reduction in storage capacity due to sediment accumulation. The objective is to analyze sedimentation processes under the combined influence of seasonal droughts, flash floods, and complex reservoir morphology. A two-dimensional hydrodynamic–sediment transport model was developed using TELEMAC-2D coupled with the GAIA sediment transport module to quantify sediment transport and deposition patterns. Flood events occurring between the 2006 and 2017 bathymetric surveys were simulated to reconstruct sediment dynamics during this period. The results reveal pronounced spatial variability in sediment deposition controlled by reservoir morphology and operational conditions, with the majority of sediment accumulating in upstream and transition zones before reaching the dam wall. Cumulative bed evolution analysis identifies five distinct regions characterized by different depositional tendencies. The results also indicate a near-linear decline in reservoir storage capacity, projecting approximately 50% capacity loss by 2040 under current management practices. To address this issue, event-based scenario simulations were conducted to evaluate potential sediment management strategies. Among the tested alternatives, a combined approach involving a bypass tunnel, diversion weir, and upstream dredging channel demonstrated the highest effectiveness, reducing sediment deposition volume by approximately 55.25% while maintaining reservoir water storage during flash flood events. By integrating modeling with decision-based evaluation criteria, the approach offers a transferable methodology for improving sediment management and sustaining reservoir storage capacity in arid and semi-arid regions facing similar hydrological and geomorphological challenges.