## 1 Introduction
[14] demonstrated that horizontal levees, as a nature-based adaptation strategy, can reduce overtopping risk by up to 30% while providing ecological benefits, particularly in scenarios of sea level rise in estuarine environments. In contrast, studies related to river bends include that of [PERSON] [15], who measured velocities in a bend of the Beaton River in Canada and observed increases in velocity with bend length and curvature. [PERSON] et al. [16] examined how channel aspect ratio, sinuosity, and curvature ratio affect flow, showing that as the aspect ratio grows, velocity variations along the main flow direction decrease markedly, whereas lateral velocity patterns remain less affected. They also highlighted the significant role of the curvature ratio in redistributing the primary flow. Moreover, [PERSON] et al. [17] investigated the influence of bend geometry on flow patterns and morphological changes, developing a new equation to predict bend scour based on secondary flow analysis and the depth of erosion. Despite these diverse studies, most remain focused on prismatic straight channel flow. In reality, rivers feature not only straight reaches but also bends, where three-dimensional (3D) flow characteristics can profoundly alter levee failure mechanisms. Because factors such as river curvature have not yet been fully incorporated into levee stability assessments, research findings obtained from straight channels cannot fully capture the complexities of actual levee breaches in curved rivers. On the other hand, work specifically targeting river bends often focuses on internal flow or sediment processes rather than extensively addressing levee failures. Consequently, although various approaches to leveee breach mechanisms have been explored, studies that address the overtopping characteristics of leveees in river bends remain limited. Moreover, many investigations focus on specific levee conditions or narrow scenarios, thereby limiting the applicability of their results to broader design or operational contexts. Therefore, it is essential to elucidate overtopping processes particular to river bends and establish an analytical framework that applies to a range of scales and conditions. Such research will ultimately facilitate a comprehensive understanding of leveee behavior in meandering rivers and contribute to more effective design and risk management of levees. Most levees are constructed using natural materials, such as soil, which significantly affects their structural stability. Soil-based levees can fail if water seeps in or overtopping occurs, especially under flood conditions, where levees sustain severe damage and may easily collapse. These considerations are critical in levee design and maintenance. Figure 1 shows the relative frequencies of different levee failure modes, categorized into overtopping, piping, and slope instability. As shown in Figure 1, among these, overtopping accounts for about 70% of failures. Overtopping mainly occurs during floods and is often observed in curved river sections where superelevation can arise [18]. For effective and economic structural measures, accurate estimation of levee overtopping in river curves plays a pivotal role in mitigating potential flood damage. In general, measures to minimize flood damage from overtopping can be categorized into two main approaches: structural and non-structural. A primary structural measure involves raising the levee crest height to prevent overtopping, whereas non-structural measures rely on legal frameworks or early warning systems rather than physical modifications. Although uncertainties associated with climate change continue to rise, structural projects such as constructing or upgrading dams and other river facilities demand extensive timelines and substantial budgets, making flexible responses to climate change challenging [23].