Impact assessment of new expansion plan on coastal lakes: case study-LakeMariout

Abstract Coastal lakes provide essential ecosystem services and economic benefits, but are increasingly subjected to hydrological modifications associated with large-scale development projects. The New Delta land reclamation project proposes modifying the lake’s water system by diverting the El-Haris drain into the 5000-acre basin and conveying water southward, raising concerns regarding potential hydrodynamic impacts. This study evaluates the hydrodynamic response of Lake Mariout to the proposed expansion plan using a two-dimensional numerical model developed with the Delft3D software package. The analysis focuses on changes in surface water levels and flow velocities under maximum operational conditions. Model calibration was performed using field-measured water levels and discharges, showing satisfactory agreement between simulated and observed results. Four scenarios were simulated, representing existing conditions, proposed diversion configurations, New Delta operational conditions, and a critical emergency shutdown case. These scenarios are designed to support decision-makers by providing insights for water management. The results indicate that water level variations across most lake basins and conveyance channels remain limited, generally ranging from 0.08 to 0.16 m. A maximum localized rise of 0.44 m was observed in the 1000-acre fishery basin without causing overtopping or hydraulic failure, suggesting no significant short-term hydrodynamic risks.