Sustainable Marine Structures

One-Line Modelling of Sediment Transport and Shoreline Evolution on a River-Dominated Coast: The Day Estuary, Vietnam

Cong Huu Vu

Key Laboratory of River and Coastal Engineering-Vietnam Academy for Water Resources (KLORCE), Chua Boc 165, Hanoi 11520, Vietnam

Xuan Hoan Le

Institute of Mechanics-Vietnam Academy of Science and Technology, Doi Can 264, Hanoi 11119, Vietnam

Nam Thanh Pham

Department of Hydrodynamics and Data Assimilation, Institute of Coastal Systems-Analysis and Modeling, Helmholtz-Zentrum Hereon, 21502 Geesthacht, Germany

Dinh Hoa Tran

Vietnam Academy for Water Resources (VAWR)-Ministry of Agriculture and Rural Development, Tay Son 171, Hanoi 11520, Vietnam

Van Chinh Pham

Center for Hydro-Meteorological Survey (HMSTS)-Vietnam Meteorological and Hydrological Administration, Phao Dai Lang 10, Hanoi 11527, Vietnam

Tien Ha Doan

Key Laboratory of River and Coastal Engineering-Vietnam Academy for Water Resources (KLORCE), Chua Boc 165, Hanoi 11520, Vietnam

Anh Tu Tran

Institute of Science and Technology for Energy and Environment (ISTEE)-Vietnam Academy of Science and Technology, Da Nang 246, Hai Phong 180000, Vietnam

DOI: https://doi.org/10.36956/sms.v8i1.2981

Received: 9 December 2025 | Revised: 20 February 2026 | Accepted: 16 March 2026 | Published Online: 20 March 2026

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Abstract

The coastline surrounding the Day estuary in northern Vietnam, extending about 25 km, has experienced rapid shoreline accretion with average rates of approximately 100 m/year, while localized erosion occurs in several sections. Previous studies suggest that long-term shoreline evolution in this region is controlled by sediment supply from the Red River, reduced nearshore wave energy, and sediment trapping by the Hoa Binh Dam. In this study, a numerical shoreline change model based on the one-line theory was applied to investigate large-scale accretion and erosion under the combined influence of riverine sediment supply and nearshore wave dynamics, while tidal currents and river flow were not explicitly simulated. The nearshore wave regime was simulated using a 2D wave transformation model driven by a 30-year deep-water wave dataset from the Global Ocean Wave Analysis (GOWA). The effect of the Hoa Binh Dam was represented by a 30% reduction in riverine sediment supply. The model was calibrated and validated against measured shoreline positions from 1965, 1989, and 2019, showing good agreement with observations and average relative errors of 9.2% and 12.5% during calibration and validation, respectively. Sediment budget analysis indicates that riverine input is the dominant source of shoreline accretion, while longshore sediment transport (LST) plays a secondary role, and part of the sediment is lost offshore. These results should be interpreted within the scope of the simplified one-line shoreline model, which targets large-scale, long-term shoreline evolution.

Keywords: Shoreline Modelling; Sediment Transport; Beach Evolution; Day Estuary; Red River

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