The Maeslant barrier is a storm surge barrier and a critical component of the Dutch coastal flood defense system. Its reliability is formally assessed through a Reliability and Availability (RA) analysis, which estimates the probability of non-closure during storm events. However, concerns have been raised regarding the completeness and transparency of this analysis, particularly the potential omission of relevant failure events. This thesis investigates whether a selected set of previously unaccounted for events can be systematically identified and quantified to improve the accuracy of the non-closure probability.

A three-stage methodology was developed. First, a structured inventory of unaccounted-for events was constructed using HAZOP, FMEA, What-If, and external event screening techniques, mapped across four analytical dimensions. Second, the list was filtered based on estimated occurrence probability and quantifiability, resulting in a shortlist of three events: epistemically uncertain events, non-stationary component degradation, and the unverified reliability of human interventions. Third, these events were quantified using structured expert judgment, research into time-dependent fault tree modeling, and human reliability assessment.

Results indicate that these unaccounted-for events can alter the estimated non-closure probability, either increasing it by an order of magnitude or reducing it by up to 50%. Moreover, the analysis revealed limitations in the current RA analysis, including outdated reliability assumptions, a fragmented integration of human interventions, and a lack of empirical data. These findings support the need for a more transparent and adaptable RA framework. The discussion highlights that while completeness in risk assessment is theoretically unattainable, similar to the limitations of physical laws, models should strive for an optimal balance between complexity, traceability, and applicability.

Recommendations include developing a centralized component lifecycle database, maintaining a registry of previously unaccounted-for events, formally integrating the OPSCHEP model into the fault tree structure, and adopting structured human reliability verification. These changes can improve the accuracy, transparency, and credibility of the Maeslant barrier’s non-closure probability and serve as a blueprint for other critical infrastructure systems. ... Read more

Sea turtle nesting beaches are under increasing pressure from climate change, rising sea levels, and human activity, making the protection of critical habitats like Ostional Beach, Costa Rica, an urgent priority. This study integrates the analysis of wave runup dynamics, groundwater behavior, stakeholder collaboration, and coastal squeeze mitigation to address the unique challenges at this vital olive ridley turtle nesting site.

Wave runup was examined using timestack imagery analysis. Two automated extraction models— entropy-only and entropy-saturation—were compared against manually digitized data. Results show that the entropy-only model is more reliable in capturing peak wave run-up values, a critical measure for understanding inundation risks. Challenges in accuracy, particularly for the entropy-saturation model, were linked to the site’s unique environmental conditions, such as dark volcanic sand. The findings fill a gap in understanding how specific extraction methods perform under unique site conditions, with implications for improving future modeling efforts.

Groundwater dynamics were studied using pressure sensors installed in custom-built wells, revealing significant interactions with tidal forces. These measurements highlighted the role of tidal cycles in influencing groundwater levels, providing crucial insights into the potential for nest inundation. These findings extend existing knowledge by combining tidal and hydrodynamic factors specific to turtle nesting sites.

Collaboration within the TURTLE project was analyzed through semi-structured interviews and structural evaluation of partner interactions. A tailored framework was developed to enhance communication and coordination among stakeholders, addressing identified gaps and leveraging existing strengths. This framework contributes to more effective project management and the application of scientific insights in conservation strategies.

To mitigate coastal squeeze—a phenomenon where natural habitats are compressed by rising sea levels and human development—the study evaluated strategies such as foreland restoration and managed retreat. Findings suggest that integrating habitat restoration with community involvement is critical to preserving the ecological and social balance at Ostional Beach.

This study takes an interdisciplinary approach to explore how wave runup, groundwater behavior, and collaboration strategies can be effectively combined to support conservation efforts. The results stress the need for tailored, site-specific solutions that blend engineering, ecological, and social perspectives to protect endangered species and their habitats. By bridging knowledge gaps and offering practical recommendations, the research bolsters both local and global initiatives aimed at preserving vulnerable coastal ecosystems.  ... Read more