| Summary: | The engineering management of river channel entrances has often been regarded as a vast and complex subject matter. Understanding the morphodynamic nature of a river channel entrance is the key in solving water-related disasters, which is a common problem in all seasonally influenced tropical countries. As a result of the abrupt increase in population centred along coastal areas, human interventions have affected the natural flows of the river in many ways, mainly as a consequence of urbanisation altering the changes in the supply of sediments. In tropical countries River channel entrances are usually seasonally driven. This has caused a pronounced impact on the topography of river channel entrances especially in the East Coast of Borneo which is influenced by both North East (NE) and South West (SW) monsoons on top of related parameters such as waves and tides, sedimentation as well as climate change. Advanced numerical modelling techniques are frequently used as a leading approach to investigate the complicated nature of river channel entrances to represent the actual conditions of a designated area. Furthermore, the conventional ‘command and control’ approach of river channel entrance management has largely failed in this region due to the lack of process based understanding of river channel entrances. This research focuses on creating a mesoscale numerical modelling method by integrating a reductionist and reduced complexity model approach, along with local seasonal conditions to represent the Petagas River channel entrance in demonstrating an actual river channel entrance. In assisting the modelling method, data and data- driven analysis is emphasised because the available resources and the subsequent adopted management strategies in solving these problems varies from country to country. The Petagas River channel entrance model is established with a set of numerical equilibrium equations and calibrated parameters to reflect the features of regional conditions with the combination of local validated modelling parameters. The model accurately represents the effects of both NE and SW monsoons in terms of hydraulics and sediment dynamics at the Petagas River channel entrance, as verified by site data and satellite imagery. The validated model serves as a predictive tool to evaluate various management solutions, which eventually helped in proposing the most viable solution. The proposed management solution includes a training channel and a breakwater resulting in an improved flushing capacity, thus preventing sedimentation and upstream flooding, allowing proper navigation through the river. This adopted solution is in accordance with local regulations and management plans that the local government adopt. In conclusion, the accurate investigational result from this numerical model successfully demonstrates its scientific role in solving problems related to a dynamic river channel entrance, and can serve as a numerical modelling approach for solving similar river channel entrance problems especially in tropical countries with predominant inter-annual seasonal variations.
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