انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Evaluation of the effects of Anzali Port Development on Sedimentation at Anzali Wetland by Numerical Simulations ارزیابی اثرات طرح توسعه بندر انزلی بر رسوبگذاری در تالاب انزلی با استفاده از شبیه سازی ریاضی 57 70 233944 10.30482/jhyd.2025.519157.1730 FA حسن حیدرنژاد فارغ التحصیل کارشناسی ارشد مهندسی آب و سازه های هیدرولیکی، دانشکده عمران، دانشکدگان فنی دانشگاه تهران پیمان بدیعی دانشکده عمران پردیس فنی دانشگاه تهران 0000-0001-6636-7612 Journal Article 2025 04 26 Introduction: Coastal wetlands, such as the Anzali Wetland in Iran, are ecologically sensitive areas that play crucial roles in environmental health, climate regulation, and biodiversity conservation. However, human activities and climate change threaten these ecosystems, leading to habitat loss and reduced ecological services. The Anzali Wetland, designated as a Ramsar Site, faces challenges like sedimentation and overgrowth of invasive species. Understanding hydrodynamics and sediment transport in these areas is vital for effective environmental management. Numerical models offer valuable tools for simulating water flow, sediment dynamics, and morphological changes in coastal wetlands. Previous studies have focused specifically and individually on the Port or Wetland but to the knowledge of Authors, none have addressed the entire wetland-port system. This study aims to fill this gap by incorporating newly acquired field data to enhance the accuracy of simulations and exploring the effects of port development on wetland sedimentation. Methodology: In this study, numerical simulations were conducted using Delft3D software to analyze the flow patterns and sediment exchange in the Anzali Wetland-Port (AWP) system. The simulations utilized the two-dimensional coupled flow, sediment, and morphology modules in the curvilinear version of Delft3D. The computational domain consisted of nine subdomains with 10,963 elements and 17,531 nodes, with a higher resolution grid in the northern port channel where calibration data were available. The model was calibrated for the period from October 31 to December 11, 2019, using measured data on daily water and sediment discharge into the system. The hydrodynamic module was calibrated by adjusting the bed roughness and turbulence viscosity coefficients, with results showing good agreement with measured velocities, especially during flood periods. For the morphology module, sediment transport parameters were calibrated based on sediment concentration and erosion/sedimentation patterns observed during the same period. The model predicted 45,000 m³ of sedimentation, which closely matched the measured 49,000 m³. Simulations were validated against measured bed level changes, showing good agreement during the calibration period. The calibrated model was applied to evaluate the impact of port development on wetland sedimentation. The results highlight the natural sediment flushing during floods, which may help reduce sediment accumulation at the piers, and provide insights into managing sediment transport in the AWP system. Results and Discussion: The calibrated Delft3D model was applied to assess two key issues: the sediment balance of the Anzali Wetland-Port (AWP) system and the impact of port development on wetland sedimentation dynamics. 1. Sediment Balance of the AWP System Simulation results reveal that the AWP system is experiencing critical sedimentation, especially within the Wetland’s floodplains. Analysis of sediment transport from incoming rivers showed a total annual inflow of approximately 661,000 m³ of sediment. Of this, 286,000 m³ is transported from the Wetland to the Port, and 237,000 m³ eventually reaches the sea. This implies a net annual sedimentation of 375,000 m³ (57%) within the Wetland and 49,000 m³ (7%) within the Port, while the remaining 36% is flushed out to the sea. The spatial pattern of sedimentation suggests that the Wetland acts as a sediment trap, with most deposition occurring in broader floodplain areas, while localized erosion is observed at the Wetland-Port boundary and within the Port itself. 2. Impact of Port Development on Sedimentation To evaluate the influence of recent Port development, especially the construction of the western breakwater, a scenario with modified geometry, facilitating flood outflow into the sea, was simulated. The new configuration involved shortening the breakwater and closing the west wing of the eastern basin to form a more direct outflow channel. This simulated results of this scenario was compared to current conditions. The results indicate that while the modification does not significantly change sedimentation within the Wetland, it substantially reduces sedimentation within the Port area—by nearly 90%. This suggests that these modifications in port layout can significantly improve sediment management and reduce dredging needs. Conclusion: A depth-averaged coupled hydrodynamic and sediment transport model was developed and validated for the AWP system using Delft3D. The model reliably simulates flow and sediment dynamics, with sediment transport being highly sensitive to physical parameters and primarily driven by flood events. Results indicate that approximately 57% of riverine sediments deposit in the Wetland, 7% in the Port, and 36% are discharged into the sea. While port geometry modifications do not impact Wetland sedimentation, they can reduce Port sedimentation by up to 90%, highlighting the effectiveness of structural interventions in sediment management. Acknowledgment This article is derived from the first Author's M.Sc. thesis and further, based on the project "Research Studies to Examine the Sedimentation Status in the Iran Commercial Ports," which was commissioned by the Ports and Maritime Organization of Iran and carried out by Khakbaft Consulting Engineers. The above is expressed as a means of acknowledgement and appreciation. تالاب انزلی، واقع در سواحل شمالی ایران، یکی از تالاب‌های بین المللی است که از سال ۱۹۷۵ در کنوانسیون رامسر به ثبت رسیده است. این تالاب بخشی از یک سامانه هیدرولیکی گسترده است که از جنوب توسط چندین رودخانه‌ تغذیه شده و از شمال، از طریق یک دهانه رودخانه‌ای به دریای خزر متصل می‌شود. یکی از چالش‌های پیش‌روی این منطقه، بررسی تأثیر توسعه‌های جدید بندری بر رسوب‌گذاری در تالاب انزلی است. برای پاسخ به این مسئله، یک شبیه‌سازی عددی با استفاده از مدلسازی دوبعدی جریان و انتقال رسوب به کمک بسته نرم افزاری Delft3D انجام شد تا الگوی جریان، انتقال رسوب و تغییرات بستر در سامانه تالاب–بندر انزلی بررسی شود. در این مدل، داده‌های هیدرولوژیکی و اندازه‌گیری سرعت جریان برای واسنجی و صحت‌سنجی مدل استفاده شد. اطلاعات به‌دست‌آمده از عملیات لایروبی و پایش‌های هیدروگرافی پیاپی نیز برای تعیین الگوهای رسوب‌گذاری و فرسایش در ناحیه بندر و تنظیم مدل مورفولوژی به‌کار رفت. نتایج نشان می‌دهد که حدود ۵۷٪ از رسوبات ورودی به سامانه تالاب –بندر انزلی در تالاب ته نشین شده، ۷٪ در حوضچه‌های بندر رسوب می‌کند، و ۳۶٪ به وارد دریای خزر می‌شود. همچنین، تغییر هندسه موج‌شکن بندر تاثیر قابل‌توجهی بر افزایش رسوب‌گذاری در تالاب نداشته‌، اما می‌تواند رسوب‌گذاری در محدوده بندر را تا ۹۰٪ کاهش دهد.

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