In times when the Dutch coastline faces pressure from coastal erosion due to the growing challenges of sea-level rise, sustainable coastal policies are essential. Increasingly large and more voluminous maintenance works are required. New sand nourishment strategies, such as mega-nourishments, are being tested along the Dutch coast. Due to the enormous quantities of sand, local safety standards increase. One example of such a project is the Hondsbossche Dunes (HBD). Although its primary function is the realization of local flood safety near the former sea dike, it also feeds nearby coast and dunes caused by natural forces like waves, currents, tides, and wind. Understanding rates and quantities of sediment dispersion to see how coastal state indicator evolve (e.g. coastal volume, beach width and depth contours) is crucial for policymaker. They must maintain the coastline as its main function of flood defense for the future, while also accommodating recreation and nature.

Literature demonstrates that one-line alongshore transport models can predict general coastline evolution trends at mega-nourishment sites well. However, their accuracy at other coastal state indicators can be limited due to, for example, the exclusion of cross-shore sediment redistribution. Recent efforts have focused on coupling such a one-line transport model (ShorelineS) with a new cross-shore redistribution model (Crocodile). Compared to other model types, the advantage of this coupling is its ability to calculate large spatial and temporal scales with minimal computational time. Additionally, the coupled model now accounts for a depth-dependent component by including this Crocodile model for the redistribution of sediment in cross-shore direction.

A data analysis of the coastal evolution at the HBD for the first 9 years was carried out. It shows that most volumetric changes occur in the initial 3 years. Furthermore, the data reveal that cross-shore activity varies over the depth. This becomes most evident from quantitative differences in volumetric changes for different vertical coastal cells (e.g. dune, beach, surfzone, shoreface). Also the differences in their correlation to the shoreline change suggest depth-dependent activity. For the models, this implies that the coupled model is likely to represent the magnitude and behavior of the volume (cells) and depth contours better.

The model comparison consist of the ShorelineS model, and ShorelineS+Crocodile (coupled model). An existing HBD ShorelineS model is extended with 4 years from 2020 to 2024, and includes a dune module, which enables the models to simulate the dunefoot and therefore provide insight in the beachwidth indicator. For the coupled model, Crocodile is used as a cross-shore module within ShorelineS that is configured with a dynamic equilibrium, and a alongshore varying and curved equilibrium grid, for its best performing run (SC5).

The results of the study suggest that the SC5 simulation improves ShorelineS on the volumetric evolution indicator; it halves the error to 250 m/m3 in 3 years time and it followings the temporal trend at the erosional zones very well. Additionally it adds new value and insight with the development of the cross-shore profile at every timestep. Although the magnitude is not yet always accurate, the SC5 simulation is able to represent independent evolution of depth contours. Despite its shown potential, the model results are constrained due to significant instabilities that appear in the model. These instabilities stem from a growing gradient-the difference in slope of the initial and equilibrium profile-which is posed by a bad translation of the equilibrium grid to a profile.

This research therefore recommends first and mostly to improve and solve the spatial and temporal stability as described above. This is necessary to make long-term predictions and contribute to future coastal maintenance strategies in the face of rising sea levels. Other relevant recommendations include creating a more realistic diffusion coefficient in Crocodile that balances subaerial and subaqueous changes better, integrating subaerial volume changes of Crocodile with ShorelineS' dunemodule in order to make a comprehensive comparison, and finally including location specific nourishments via Crocodile module and consequentially account for profile adjustment. ... Read more

In Vietnam, the fishery sector is vital for the economy. The government strives towards an increase in fishing activities in the coming years. The Quy Nhơn port, a key hub in central Vietnam, is set to accommodate more international vessels. This means local fishermen must rely on other ports like Đề Gi, which also needs upgrading to meet aquaculture production goals. To support the fishing sector's growth in Bình Định province, the Khu neo đậu đầm Đề Gi (KND) project is initiated by the local authorities and will contribute to upgrading the Đề Gi port and construct a new storm shelter. However, this project has potential issues: (1) it focuses mainly on storm shelter capacity and does not address the increase of traffic in the current network capacity, (2) the estuary suffers from sedimentation issues, limiting the nautical accessibility of the access channel, resulting in a decrease of port and storm shelter functionality. To tackle these problems the following main question is investigated:

What is the current performance of the Đề Gi port and storm shelter system, and how can engineering methods be used to assess its potential for future growth within the broader context of sustainable socio-economic development?

The main research question is going to be supported by the following sub-questions:

How will the current logistic service network perform in the future vision as foreseen by the responsible authorities and how to verify it with an engineering responsible approach?

How to examine the accessibility of the port and storm shelter in the KND project, while ensuring a safe, robust, durable and effective system?

What are the consequences of the port and storm shelter upgrade on the logistical system and on the conditions in the waterway and what impact does this have on the Đề Gi area?

The main aim of this research is apply engineering methods to understand the system in order to assess its performance and put this in the context of the socio-economic development of the Đề Gi area and the Bình Định province. To achieve this, various research methods are used to analyse the current state of logistic service and nautical accessibility, to identify the bottlenecks in the systems. To include the aspect of incorporating the socio-economics in a broader context of the area, a stakeholder analysis is introduced. For the inland logistic services of the port, a qualitative 4(+1)-transport modelling model is established. For investigating the nautical accessibility, a comprehensive system analysis, including the topics of (1) climate, (2) hydrodynamics, (3) morphodynamics and (4) current and future conditions of the access channel, is conducted to provide insights into nautical accessibility challenges to enhance the safety, robustness, durable and effectiveness of the access channel.

To analyse the logistic service system in the area, field observation in combination with interviews are performed to have a concrete insight into the characteristic harbour patterns, traffic and transportation system and the current transportation network for the goods originating from the harbour. Additionally, various development plans and visions outlined by local authorities are reviewed to gain a comprehensive understanding of the area's future development. By evaluating the current state of the logistic service network alongside the region's development plans, the limitations within the network are identified. The primary bottlenecks in the logistic services system predominantly revolve around capacity and quality issues in the existing road network. Many of these limitations are expected to be addressed through the implementation of the local authorities' development visions. However, for a reliable conclusion, an engineering approach is necessary. To achieve this, a 4(+1)-step transport modelling, coupled with an All-Or-Nothing traffic assignment, is recommended. For the examination of the Đề Gi road network and traffic assignment, this approach provided an initial assessment of the intensity of each link within the study area relative to its corresponding capacity.

The second sub-question is addressed through an analysis and depth assessment, uncovering critical nautical accessibility bottlenecks. These include draught limitations and climate change impacts, potentially compromising safety, robustness, durability, and effectiveness. A depth assessment, considering different vessel types and water levels, provides insights into the current channel status. Safety is a major concern, especially for larger vessels during low water conditions, heightened by climate change. Robustness faces challenges due to sedimentation and storm vulnerabilities. Durability is threatened by changing climate conditions affecting sediment dynamics and storms. Effectiveness remains relatively stable, with 90\% accessibility for the expected future vessel fleet. These findings particularly point to the need for safety and durability measures, especially in light of future climate change predictions, necessitating climate-resilient design.

The third sub-question explores the port and storm shelter upgrade's impact on Đề Gi. Consequences include increased traffic and vessel intensity, on land and through the access channel, and a shift in vessel fleet mix, requiring improved infrastructure and access channel design. This enhances safety and, ultimately, drives socio-economic growth, education, and investment appeal in the Đề Gi area.

In the Đề Gi area, current transportation capacity falls short of future growth needs. Local authorities' development plans aim to resolve logistic service bottlenecks. Nautical accessibility is currently 90\% effective but not consistently safe. Climate change threatens its durability. Engineering models, like the 4(+1) step methodology and comprehensive system analysis in combination with a depth assessment, uncover transport and nautical accessibility challenges. These methods assess future impacts of the port and storm shelter upgrade, benefiting the Đề Gi area with socio-economic development, improved safety and new opportunities for the local community. ... Read more