*2.1. The Front of the Terrace* 2.1.1. The Attack Shore

Lin et al. showed that riverbank erosion mainly occurs at the bends in the river courses and tends to be most severe at the outer edges of such bends, called the attack shore (or cutting slope) [16]. The riverbank located on the attack shore has been eroded by the river for a long time, and the soil and rocks detached by such erosion are constantly being carried away by the river water, causing the toe to be gradually emptied; over time, this makes the riverbank steeper until it collapses. Roads and building foundations on the top are then damaged, or in some cases completely destroyed, due to loss of support. Lin et al. also noted that the movement of sandbars is mainly affected by five factors, i.e., the presence or absence of bends in rivers, the degree of such bends' curvature (known as meander), the presence or absence of confluent lateral structures, the way the river is scrubbed, and the supply of soil and sand [17]. Generally, convex-bank sandbars in curved sections of a river are more developed, and water flows mostly to the concave bank—i.e., the attacking shore—to erode it. Su concluded that, when the river flows through the attacking shore, flow velocity increases, and the centrifugal vortex water is formed there, washing it and transporting soil and sand to the convex bank [18].
