The stability of superficial sediments of an actual artificial shallow constructed in a pilot project is investigated by using a three-dimensional coupled fluid-sediment interaction model in terms of the Shields parameter (SP) and a relative vertical effective stress ratio (RESR) in the surface layer of the shallow. The wave action causes the erosion at the seaward edge of the crown, the upper part of the seaward ridge, and the center of the landward slope, and the deposition at their adjacent areas. These topographic changes are related to large values of the averaged SP, while the values of RESR around the eroded areas are larger than those at the other areas, resulting in the acceleration of the sediment transport. The topographic change of the shallow is evaluated more reasonably by using a SP modified with RESR.
