A tailored hybrid risk assessment model for coastal flow slides along with management strategies

Abstract

Coastal flow slide (CFS) is a type of landslide that occurs in coastal areas, where a mass of soil and rock flows downhill. It can be divided into two categories: breaching and liquefaction, which have different mechanisms and sand movement dynamics, but both lead to the same result: a large mass of sand and other materials flowing downslope. Breaching, coastal retrogressive breaching flow slides (CRBF), the first type of coastal flow slide, happens in densely packed sand. It starts when the sand grains dilate, or spread apart, which creates negative pore pressure. This causes the sand grains to flow downhill one by one, in a gradual process. Liquefaction flow slides (LFS), on the other hand, is a more abrupt process because the sand suddenly loses its strength and flows like a liquid. Although this topic has been discussed in the literature, there are only a few studies on it. One of the biggest challenges in CFS is that these hazards often start below the water surface. This makes them difficult to identify and study in detail. The complexity of underwater conditions also makes it difficult to analyze these hazards, and the lack of knowledge on this topic also indicates a significant gap in risk management. Given the challenges of studying coastal flow slides, it is clear that new and innovative approaches are needed. This study introduces a novel sensitivity index and a sophisticated hybrid model that can be used to gauge the risk of coastal flow slides and identify vulnerable coastal regions. The hybrid model comprises five distinct components: Bayesian Network (BN): used to represent the complex relationships between the various factors that contribute to coastal flow slides. Experimental study (ES): conducted laboratory and field experiments to investigate the physical processes involved in coastal flow slides. Site inspection (SI): visited coastal sites to collect data on the local conditions that may influence the risk of coastal flow slides. Sensitivity index development (SID): used to quantify the relative importance of different factors in contributing to coastal flow slides. The hybrid model identified beach slope, sediment configuration and compaction, mass flow, and the existence of turbidity currents as the key variables that differentiate CRBF and LFS failures. To effectively handle the specific need of distinguishing between these two types of coastal failures, a tailored sensitivity index was developed in alignment with the hybrid model. This comprehensive metric incorporates various factors such as beach slope, sediment characteristics, and mass flow incidence, all crucial for assessing coastal vulnerability to failures like CRBF and LFS. The hybrid model not only identifies key variables like beach slope, sediment configuration, compaction, mass flow, and turbidity currents but also examines additional parameters. These parameters offer valuable insights into coastal management strategies associated with these key variables. These additional parameters offer valuable insights into how the key variables are connected to strategies for coastal managment. This study offers a novel approach by integrating the complementary strengths and functionalities of several models, (BN, ES, SI, SID), enabling researchers to make significant contributions to research in: (a) expanding the scope of application by developing new methods for coastal flow slides; (b) considering a wider range of variables relevant to CFS; (c) analyzing variables that can have a significant impact on flow slides; (d) developing methodologies for coupling coastal flow slide projections with reliable outcomes.