## 1 Introduction  
The coastal zone connects the ocean and the land, has excellent resources and environmental conditions, and is closely related to social production and construction activities [1]. Since the 1970s, sea reclamation, salt pan use, and port construction have developed rapidly along the coast of China. As urbanization and industrialization continue to advance in coastal areas, the demand for land resources has increased dramatically. In order to expand the space for social development, the utilization of seaward mudflats has become an important approach to resolving the contradiction of land scarcity suitable for development [2, 3]. In the development and utilization of the entire coastal zone, pays occupy a particularly important position. With sufficient sediment sources and certain hydrodynamic conditions, semi-enclosed bays often develop silt coasts. This type of coast has flat terrain, wide beaches, and shallow waters. In addition, it has a superior geographical location and abundant natural resources, making it a more suitable area for reclamation activities. Mudflat reclamation has multiple impacts. It not only directly alters the geometry of the original shoreline but also induces changes in the hydrodynamic environment. Specifically, it causes a decrease in flow velocity, a reduction in tidal range, and a weakening of the tidal prism within the bay, as documented in references [4, 5, 6]. These changes lead to a diminishedcapacity of the water body to hold sand in the harbor and accelerate the siltation process within the bay, thereby affecting the evolution trend of the mudflat [4]. Furthermore, mudflat reclamation exerts a negative influence on the ecological environment. It gives rise to the deterioration of the bay's water quality and intensifies the eutrophication of the water, resulting in a series of ecological problems [7; 8]. Laizhou Bay is located in eastern China, in the southern part of Bohai Sea in Shandong Province. It is the largest bay in Shandong Province. The water depth in the bay is mostly less than 15 m, with the maximum depth being 22 m, located at the high corner of Qom Island [9]. Laizhou Bay is one of the bays where reclamation activities were carried out earlier in China. Long-term tidal flat reclamation has led to significant changes in the type and structure of the bay coastline, and has shown obvious stages of characteristics [10; 11; 12]. Before the 1970s, the natural coastline of the bay accounted for a high proportion of the total, and coastal development activities were mainly based on salt pan use. In the 1990s, the artificial coastline accounted for nearly 50%. Development activities such as maritime, salt pan utilization, and port-related sea use increased significantly. Since the start of the 21 st century, the artificial shoreline has held an absolute advantage, and development activities like port-related sea use and maritime have surged sharply. Long-term human activities are bound to change the hydrodynamic environment of the bay. In the past, most studies on the range and tidal prism of Laizhou Bay focused on the local impact of a specific coastal project [3; 13; 14; 15; 16; 17; 18]. However, due to the dispersion and lag of the impact of multiple reclamation projects on the hydrodynamic environment, it is necessary to conduct a systematic and comprehensive study on the long-term cumulative effects of shoreline changes on the tidal range and tidal prism in Laizhou Bay. The morphology of the coastline in the southwestern part of the bay has changed significantly in the 20 years from 2000 to 2020, and the length of the artificial coastline has increased by nearly 50% in more than 10 years [12]. Remote sensing images and chart data were used to carry out numerical simulation and comparative analysis for the purpose of studying the impact of the southwestern Laizhou Bay's coastline changes over the past 20 years on the tidal range and tidal prism in the sea area.