With increasing threats from climate change, the vulnerability of coastal areas is heightened. One major challenge is the degradation of beaches due to flooding and erosion. Tropical and subtropical beaches are crucial nesting sites of sea turtles who are essential to marine ecosystems by supporting the preservation of coral reef and transporting nutrients from the ocean to coastal environments. Developing engineering maintenance or designing nature-based solutions can help mitigate the effects of flooding and erosion, preserving or expanding sea turtle nesting beaches. To effectively develop nature-based solutions that enhance sea turtle beaches by improving nesting suitability and reducing flooding and erosion, an understanding of the natural processes on small-scale environmental variables, such as sediment characteristics, are essential. The sediment characteristics are important for the survival of sea turtles because they influence the nesting behavior, egg survival and hatching success. Unfortunately, current data on sediment characteristics are scarce, especially at a global scale, which makes it difficult to identify global patterns of these characteristics across sea turtle nesting beaches.

The aim of this study was to analyze key sediment characteristics of sixteen globally significant sea turtle nesting beaches and to evaluate different experimental methods to investigate these sediment characteristics as a pilot study. The key sediment characteristics in this pilot study included color, particle size, particle grading, particle shape, bulk density, solid particle density, angle of repose, thermal retention, and porosity. This research served as a pilot study for a more extensive analysis that will be applied to approximately 2000 sediment samples from 209 sea turtle nesting beaches worldwide.
To achieve this, 32 sediment samples were examined from sixteen beaches, with one sample taken from the nesting line and one from the shoreline at each location. The nesting line was identified by visible nests and body pits, while the shoreline was defined as the highest point of debris left by the retreating tide. The sediment samples were analyzed using both qualitative and quantitative methods in different laboratories (TU Delft, Boskalis and Deltares). Qualitative methods included the Munsell color chart, Power scale, classification of sorting (well-sorted vs. poorly sorted), sand ruler and LEICA digital microscope.
Quantitative methods included dry sieving, Dynamic Image Analysis (DIA), Static Light Scattering (SLS), free-fall \& vibration table, volume of water displacement, helium gas displacement pycnometer, image-based angle of repose analysis and thermal retention analysis.

The results showed that all sixteen nesting beaches in this study were composed of well-sorted, medium-sized sand. These beaches may also be characterized by particles with moderate roundness and high circularity. Variations in bulk density and solid particle density suggested that sea turtles nest in diverse beach conditions, without a clear preference for specific density values. Results for angle of repose and thermal retention did not yield meaningful patterns related to sea turtle nesting preferences. Porosity values were consistent with those typically found in sandy environments. However, definitive conclusions about sea turtle nesting preferences can not be drawn at this stage, given the limited sample size and the lack of comparative data from non-nesting beaches. The findings should be considered suggestive rather than conclusive, and their main purpose is to guide future research directions.

This study also identified differences between key sediment characteristics at the nesting- and shoreline. While some variation was observed, no general statically significant differences were found between these two environments. Based on these findings, future large-scale studies may consider initially focusing on the sediment samples at the nesting line. No clear relationships were observed between sediment characteristics and latitude, and sea turtle species did not show distinct preferences for specific sediment characteristics. However, these findings should be further investigated with a large number of sampling sites.

For large-scale sediment analysis, DIA would be the most efficient alternative to analyze particle size and it also provides information on particle shape. Although dry sieving remained the most reliable method, it might be time-consuming for analyzing a large number of sediment samples. Regarding solid particle density analysis, the helium gas pycnometer seemed to be the most accurate option. However, it required professional expertise. Nevertheless, no significant differences were revealed between results obtained from the gas pycnometer and the volume of water displacement. The reliability of the water displacement method remained uncertain, and further testing was necessary to validate its accuracy or consider alternative methods.

Based on the outcomes of this pilot study, future research is recommended to pursue a more comprehensive and globally representative understanding of sediment characteristics at sea turtle nesting beaches. This will involve analyzing sediment samples from 209 beaches, focusing on the nesting line. The extended study will asses key characteristics, including color, particle size, particle shape, bulk density, solid particle density and porosity. The resulting dataset will provide essential information for researchers, ecologists and coastal engineers, and may contribute to the development of nature-based solutions, such as beach nourishment, to protect sea turtle nesting areas.

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.