## 3 Results and Discussion
### Changing Geometry of the Southwestern Gulf
To further explore the details of the coastline changes in Laizhou Bay, we calculated the change values of the local typing dimensions of the shoreline before and after the corresponding locations based on the 143 sections extracted above, and correlated them with the EPR results (Figure 2). It can be seen from the figure that the EPR changes present a bimodal distribution pattern with a significant tail in the positive direction, indicating that the overall trend is towards growth. Due to the limitations of their own properties, the erosion and dynamic equilibrium zones show strong concentrated distribution characteristics. In terms of local fractal dimension changes, the fractal dimension changes of the three shoreline types are highly consistent, and all show symmetrical distribution characteristics. Among them, the fractal dimension changes in the dynamic stability zone appear more discrete than those in the growth zone, and tend to decrease, forming an obvious secondary peak near \(-0.35\). The fractal dimension changes in the growth zone are more concentrated; since the growth zone has an advantage in the number of coastlines, the overall fractal dimension of the coastline shows an increase of 5.8% overall. The calculation results of EPR show that over the past 20 years, most of the bay area's coastline has been in a growth trend of advancing toward the sea, 85.3% of the cross-sections are growth areas, 11.9% are dynamic stability areas, and there is almost no erosion area (only 2.8%). In the dynamic stability zone, the average coastline change rate is \(-0.14\) m/a; in the growth zone, the average coastline change rate reaches 212.06 m/a; in the erosion zone, the average coastline change rate is \(-8.70\) m/a. In general, the coastline of Laizhou Bay has shown a growth momentum over the past 20 years, with its length increasing from 315.97 km to 515.89 km, which is an increase of 63.27%. This also caused the sea area in the southwest of the bay to decrease from 4202.51 km\({}^{2}\) to 3712.42 km\({}^{2}\), which is a decrease of 11.66%; the center of mass moved 2.22 km to the northeast. By combining remote sensing images with field survey data, it has been determined that land reclamation activities--primarily for aquaculture, port terminal construction, and breakwater development--are the main drivers of morphological changes in the southwestern part of the bay. Overall, between 2000 and 2020, the geometric shape of southwestern Laizhou Bay changed significantly due to the influence of natural factors and human activities (Figure 3). The natural silting and erosion of the coastline are mainly located near the new and old Yellow River mouths formed by the Qingshuigou flow path. In 1976, the Yellow River was redirected from the Diaokou River to the Qingshuigou River. As a result, the river has since carried a significant amount of sediment into the sea, leading to continuous silt buildup at the river mouth, particularly to the southeast. In 1996, after the river mouth was artificially diverted from southeast to north, a new estuary began to form in the north [40]. Due to the diversion of the river mouth and the lack of sand supply, the old Yellow River estuary coastline has continued to erode and retreat to the land, while the new Yellow River estuary coastline has continued to silt up towards the sea due to the long-term supply of sand. The coastline outside the Yellow River estuary is mainly affected by human activities, and a series of changes have occurred, including general expansion from land to sea, a sharp increase in the length and proportion of artificial coastline, and a gradual reduction in the area of the bay. The formation of aquaculture dikes, port and wharf coastlines, and breakwater coastlines are the main driving factors causing coastline changes.