Beach Erosion Characteristics Induced by Human Activities—A Case Study in Haiyang, Yellow Sea

Abstract

Coastal zones, which serve as transitional areas between land and sea, possess unique ecological values. Sandy coasts, celebrated for their distinctive natural beauty and ideal recreational settings, have garnered significant attention. However, uncontrolled human activities can exacerbate erosion or even trigger more severe erosion along these coasts. This study utilizes unmanned aerial photography and typical beach profile survey data collected from the main areas of Wanmi Beach over the past eight years to quantify annual changes in beach erosion and elucidate the erosion characteristics and their variations across different shore profiles. Additionally, the impact of various types of human activities in different regions is analyzed, revealing the erosion patterns prevalent in the main areas of Wanmi Beach. The findings indicate that the eastern research area (ERA) has been in a continuous state of erosion, primarily due to a reduction in sediment supply in the region, with severe erosion observed on the foreshore of Fengxiang Beach and Wanmi Bathing Beach (WBB). In contrast, the central research area (CRA), particularly around Yangjiao Bay, has experienced significant siltation in recent years, with the highest siltation volume recorded between 2021 and 2023, totaling 90,352.91 m³. Nevertheless, the foreshore areas at both ends of the research area, distant from Yangjiao Bay, have been subject to erosion. The western research area (WRA) is notably impacted by surrounding aquaculture activities, leading to alternating periods of erosion and siltation on the beach surface. Consequently, due to the influence of human activities on different shore profiles, most of Wanmi Beach, except for the area near Yangjiao Bay, is experiencing erosion.

1. Introduction

The coastal zone, representing the intersection of land and sea, encompasses a unique ecosystem and is abundant in natural resources, including fisheries, minerals, renewable energy sources, and valuable tourism opportunities [1,2,3,4,5]. These resources are vital for human survival and development [6,7,8].

Coastal erosion refers to the retreat of shorelines and the degradation of intertidal mudflats and subtidal zones due to the action of waves, tidal forces, and currents. Sand beaches constitute more than one-third of the global coastline [9]. Approximately 70% of China’s sandy coasts and some muddy coasts have suffered erosion to varying degrees, with about 49.5% of sandy beaches experiencing severe erosion [10,11]. This phenomenon, primarily occurring in coastal zones, poses significant threats to environmental stability and resource utilization in these areas. Both natural and anthropogenic factors can contribute to coastal erosion. Long-term influences such as climate change, alterations in runoff, and rising sea levels exacerbate this issue [12]. In 1962, Bruun’s Law was proposed, positing that coastal erosion is driven by sea level rise [13]. Subsequent research has built upon this foundational work, continuously exploring the mechanisms through which sea level rise contributes to erosion [14,15,16,17,18,19,20]. Extreme weather events can also destabilize sandy shores [21,22,23,24]. In addition, human activities—including coastal construction, sand mining, beach farming, channel dredging, and land reclamation—have significantly disrupted the stability of sandy coasts.

Human factors, such as coastal engineering and construction, coastal aquaculture, and the development of artificial islands, can contribute to beach erosion, disrupt the equilibrium of beach systems, and cause irreparable damage to coastal environments [25]. In Ghana, beaches are experiencing significant erosion due to extensive coastal development and the proliferation of tourism projects [26]. The construction of coastal infrastructure can alter the depositional dynamics of beach environments, thereby affecting shoreline changes. For instance, the construction of dams along the coastal beaches of the north-western Bohai Sea has diminished sediment sources, resulting in accelerated coastal retreat. This substantial reduction in sediment supply has compromised the stability of sediment transport and the beaches’ capacity for self-recovery following storm surges. Coastal erosion is further intensified by the development of coastal projects and tourism activities [27]. Over 70% of the sandy coastline in Shandong Province is occupied by aquaculture ponds, harbors, and coastal dikes. The presence of these engineering structures has not only modified the sedimentary dynamics of the beach but has also severed sediment sources, disrupting the balance between erosion and deposition [28]. Beach aquaculture can negatively affect changes in beach and shoreline morphology to some extent. Farmers often lay culvert pipes on the beach, which damages the existing beach morphology. Additionally, the characteristics of aquaculture effluent discharge, including its timing, location, and flow rate, can influence the material budget and geomorphological evolution of sandy coasts [29]. When these factors are combined with processes such as tides, currents, sea level rise, and extreme weather events, they can cause significant damage to the beach. Additionally, due to variations in the size, offshore distance, and location of artificial islands, the construction of these islands and the implementation of land reclamation projects can alter the hydrodynamic and sediment transport conditions of the regional beach, resulting in changes in erosion and sedimentation along different segments of the shoreline. A study of the Nanhai Mingzhu artificial island in Haikou Bay, China, revealed that the corresponding beach on the island forms a seaward-protruding, tongue-like shoreline, with coastal erosion occurring on both sides [30]. Furthermore, the construction of Hainan’s Sun and Moon Island has led to rapid changes in erosion and sedimentation in Riyue Bay in the short term, with significant erosion observed on the northeast and southwest sides of Sun Island [31].

Traditional methods of coastal surveying primarily involved manual field surveys on beaches, along with direct measurements of the shoreline and topography using levels, rangefinders, and markers [32,33,34]. Subsequently, nautical charts and GPS became common tools for field investigation [35,36]. However, these methods are labor-intensive, inefficient, and exhibit relatively low accuracy. As technology has advanced, many modern techniques, such as satellite remote sensing, Unmanned Aerial Vehicles (UAV) equipped with LiDAR, multi-beam sonar systems, and Synthetic Aperture Radar (SAR), have begun to replace or complement traditional methods. These innovations address the drawbacks, providing more efficient and precise means for conducting beach surveys [37,38].

Commonly utilized methods include satellite remote sensing and unmanned aerial photography. García-Rubio et al. investigated a method for extracting satellite-derived shorelines that is less biased than in situ shoreline measurements [39]. Luijendijk et al. provided an up-to-date global-scale assessment of sandy coastline dynamics, based on 33 years of satellite image analysis [9]. Hagenaars presented an automated method for extracting coastlines from satellite imagery, facilitating both long-term and local-scale analyses of coastline trends [40]. In comparison to satellite remote sensing, UAV aerial photography offers advantages such as rapid response, high resolution, low cost, and real-time operation, making it particularly suitable for coastal zone mapping. Pianca et al. utilized aerial video to develop a shoreline extraction model for analyzing shoreline changes [41]. Assenbaum confirmed the applicability of unmanned airborne LiDAR through measurements, enabling comprehensive surveys of coastal terrain even amid changing beach morphology [42]. Gao et al. employed a UAV with a LiDAR system to measure 10,000 m of beach in Haiyang, Yantai, demonstrating its effectiveness for coastal erosion monitoring within a short time frame and its adequate accuracy for monitoring dynamic coastal changes [43]. Laporte-Fauret et al. conducted LIDAR-equipped drone surveys of the beach to investigate coastal dune shifts and shoreline changes [44]. Lei et al. utilized a UAV with a LiDAR system to collect topographic data from beaches in Zhejiang Province, China, at multiple time points, to examine how beach topography and geomorphology respond to typhoon events [45]. Lin et al. monitor rapid shoreline changes through UAV-based remote sensing [46]. Currently, beach measurement methods are developing rapidly, with techniques such as Synthetic Aperture Radar (SAR) and deep learning being progressively refined and applied to coastal surveys [47,48].

China’s sandy coast, which extends approximately 2670 km, is subject to significant erosion, particularly along the sandy beaches of Liaoning, Hebei, Shandong, Fujian, and Guangdong Provinces. Notably, nearly 70% of the sandy coasts and almost all silty coasts are experiencing erosion to varying degrees [49]. The sandy coast of the Eastern Shandong Peninsula, particularly in Rizhao, Qingdao, Weihai, and Haiyang City, which falls under Yantai’s jurisdiction, is of particular interest. The beach in Haiyang City, renowned for its fine sand, stable waves, gentle slope, and clear water, extends nearly 20 km and has earned the moniker “10,000-m beach.” However, the natural morphology of Haiyang City’s beaches has been significantly altered by tourism development, over-exploitation of the coastal zone, and beach farming. The erosion of sandy coasts, especially due to the construction of artificial structures, is most pronounced in this area [50,51]. Although the construction of man-made structures has largely ceased in recent years, their cumulative effects continue to impact the stability of the sandy coast in the “10,000-m beach” region. Following the construction of the artificial island, Lianli Island, near the ten-thousand-meter beach in Haiyang City, Yantai, Shandong Province, the central beach area has exhibited a general state of weak sedimentation; however, localized erosion has been observed on the eastern and western sides of the beach [52]. Wei et al. [51] discovered through monitoring and interpolation calculations of beach profile elevations that the Wanmi Beach Bathing Area on the eastern side of Wanmi Beach has experienced overall erosion, with the most severe erosion occurring on the high tide beach face in the central region. Xie et al. [53] investigated the beach profile morphology and surface sediment grain size along Wanmi Beach in Haiyang, Yantai, and analyzed their findings. They noted that the summer trends are similar to those of winter, with only minor seasonal differences. Furthermore, they concluded that the construction of artificial islands and other coastal projects, along with human activities, are the primary factors driving changes in beach profile morphology. Thus, it is crucial to explore the characteristics of erosion and sedimentation changes, the current status, and the responses to human activities at Wanmi Beach in Haiyang City, Yantai.

In this study, the UAV-based airborne LiDAR was applied to investigate Wanmi Beach in Haiyang City, quantifying changes in beach volume over the years. In addition, beach profile elevation data have been supplemented. It focuses on the erosion and sedimentation characteristics of the beach over the years, as well as its response to human activities, using both quantitative calculations and qualitative analysis.

2. Data and Methodology

2.1. Overview of the Study Area

Haiyang City, a subordinate of Yantai City in Shandong Province, is located on the southern coast of the Jiaodong Peninsula, bordered by the Yellow Sea between 120°50′E and 121°29′E, and 36°16′N and 37°10′N. Haiyang City is one of the most important satellite cities of Yantai. Haiyang serves as an important hub connecting the economically developed cities of Qingdao and Yantai. The coastline extends approximately 230 km from the northwestern shore of Dingzi Bay to Guantang Bay on the southwestern side of Yushan Bay, including a 120 km segment of sandy coastline from Dingzi Bay to Guantang Bay [50]. The study area begins at the midpoint of Binhai West Road at Wanmi Beach and stretches along the coastline to the western boundary of Haiyang New Harbor. This area encompasses two core zones: Fengxiang Beach, located east of the Lianli Island Bridge up to the vicinity of the P9 profile, and Wanmi Bathing Beach (WBB), situated to the east of the P9 profile. This profile of the beach, a rare, straight open sandy coast in Shandong Province, is renowned for its sand sculpture construction, beach volleyball, and tourism. In addition, this section of the beach is also influenced by various human activities. On the western side of the study area, a significant amount of beach aquaculture activity is distributed behind the beach. The construction of Haiyang Port on the easternmost side and the artificial island near Yangjiao Bay, known as Lianli Island, will also have an impact on the beach to some extent. The distribution of human activities in this area makes it an excellent case study for research on sandy coastal erosion, illustrated in Figure 1.

Lianli Island, which consists of two artificial islands, received approval from the State Council in January 2009. It spans a total area of nearly 1.8 million m² and is recognized as the first offshore artificial island in Northern China. The islands are connected by a 1500 m long permeable sea sightseeing bridge, which enhances interaction between land and sea, effectively linking the islands with the adjacent beaches.

The study area experiences a regular semidiurnal tide, characterized by an average tidal range of 2.39 m. Wind-driven waves are predominant, with average heights ranging from 0.5 m to 0.8 m. In spring, the primary wave direction is from the SSE, while in autumn, the strongest waves originate from the SSW [52] (Figure 2). Thus, the normal wave direction of the study area is SSE, and the secondary normal wave direction is SSW. The wave height in winter and autumn is significantly lower than that in summer. The unique ocean dynamics of the study area are shaped by the interplay of its tides, currents, and waves.

Sediment sources in the study area include the Dongcun River, located near Yangjiao Bay, as well as silt and sand from Dingzi Bay and Rushan Bay. Dingzi Bay, situated approximately 10.4 km west of the study area, serves as the most significant source of sediment supply, with its sediment being transported from west to east under the influence of littoral currents. Additionally, the Dongcun River near Yangjiao Bay contributes silt and sand to the area [54]. The hydrodynamic conditions of the study area’s beach are relatively stable, exhibiting weak seasonal variations [53].

2.2. Source of Data

This study utilized UAV aerial photography in conjunction with GNSS RTK (Global Navigation Satellite System Real-Time Kinematic) measurements to assess beach profiles. In recent years drone aerial photography has emerged as the primary technical method for monitoring coastal shoreline topography. In April 2017, aerial photography was conducted during both high and low tides—using a DJI M600 PRO drone (Shenzhen, China) equipped with a PHASE ONE IXU-1000 camera (Copenhagen, Denmark). For each coastal profile, two flight routes were established along the coastal alignment at an altitude of 120 m, achieving a ground sample distance (GSD) of up to 2.5 cm, with 70% overlap in the flight direction and 80% sidelap. Before aerial photography, image control points were evenly distributed across the site, ensuring no more than 150 m between them. Aerial photography was synchronized with GNSS RTK measurements to collect elevation data for specific points. Since 2017, Unmanned Aerial Vehicles (UAVs) equipped with LiDAR for beach measurement tasks have been applied. The effective measurement range of LiDAR can reach up to 450 m under 80% lighting conditions and 190 m under 10% lighting conditions. During beach measurements, our UAVs typically fly at an altitude of 70 m, achieving a planimetric measurement accuracy within 10 cm and a vertical data accuracy within 5 cm. The aerial image data from six periods, November 2017, October 2018, November 2019, October 2020, November 2021, and November 2023, was collected and processed using DJI Terra V4.0.10 to generate point cloud data for each period.

GNSS RTK was applied to acquire signals from the CORS (Continuously Operating Reference Stations) network in Shandong Province. The survey was conducted during the low tide of the spring tide and involved data collection from 11 profiles over seven years, from 2016 to 2022. Prior to observing each profile, a comparison was made at the profile’s starting point, which served as an E-level GPS control point. The differences observed during this comparison were maintained within 2 cm in planar distance and 5 cm in elevation. Sampling measurements were taken from the starting point toward the sea along the deployed monitoring profile, with an average sampling interval not exceeding 1.5 m. In regions characterized by significant terrain undulation, such as the beach berm, sampling points were densified. Each measurement point was required to deviate no more than ±0.1 m from the designated survey line.

The advancements in LiDAR technology have significantly enhanced the quantitative assessment of beach erosion, providing researchers and coastal managers with powerful tools for monitoring and analyzing coastal dynamics. The use of UAVs equipped with LiDAR in this research has been shown to effectively map sandy coasts. This technology facilitates the collection of high-resolution topographic data, which is essential for understanding erosion and accretion processes in sandy coastal areas.

The UAV equipped with LiDAR can produce denser point clouds and capture more detailed morphological features of the beach, which is essential for accurately assessing changes in coastal topography over time. The capability of LiDAR to generate Digital Elevation Models (DEMs) with high spatial resolution facilitates a detailed analysis of beach morphology and the identification of erosion hotspots. In this research, the LiDAR point cloud data, which included over 17,670,584 points in a single survey, provided a comprehensive view of the coastal landscape, enabling researchers to quantify volumetric changes associated with erosion and sediment deposition. This high density of data points enhances the detection of small-scale features that are often critical for understanding the dynamics of sandy coast erosion. Furthermore, the integration of UAV LiDAR data with other beach profile elevation measurement data compensates for the deficiencies of both monitoring methods. This multi-faceted approach allows for the continuous tracking of shoreline changes and the assessment of the impacts of extreme weather events, such as storms. However, the UAV equipped with LiDAR has certain limitations, primarily regarding its general laser ranging capabilities and poor vegetation penetration. To achieve the required measurement accuracy, the flight altitude must remain below 80 m. Additionally, the UAV equipped with LiDAR effectively addresses the time-consuming, labor-intensive, and low-precision issues associated with traditional manual beach measurement.

2.3. Methodology

After processing the point cloud data to eliminate noise and classify the points, the point cloud was converted to a vertical datum and aligned the elevations with the 1985 National Elevation Datum. To decrease the workload for subsequent processing and analysis while maintaining result accuracy, the point cloud was thinned at spatial intervals of 0.2 m.

The processed point cloud data were unified to delineate land and water boundaries, thereby facilitating quantitative comparisons between adjacent years. The delineation of the land boundary is based on the revised coastline of Shandong Province. For the water boundary, considering that aerial photography was conducted at slightly different tide times each year, the water boundary was selected on the seaward side of the beach from the image with the smallest width as the baseline boundary. The water boundaries for subsequent years were then delineated by referencing this baseline. Due to the incompleteness of the 2017 aerial drone data, common boundaries were established for comparison during the beach volume change analysis spanning 2017 to 2018.

To facilitate comparative analysis, the beaches in the study area were categorized into three typical shore segments based on their development and utilization types, as well as their natural geographic features (Figure 3). The western research area (WRA) extends from the beach near the middle profile of West Seaside Road to approximately 1700 m west of Yangjiao Bay. In this profile, the beach berm and backshore are predominantly used for aquaculture ponds, while the foreshore remains largely undisturbed by human activities, preserving its natural state. The central research area (CRA) stretches from 1700 m west of Yangjiao Bay to the western boundary of the Lianli Island Bridge. The backshore of this segment is employed for various purposes, including aquaculture, beach volleyball, and tourism and recreation, with human activities concentrated on the beach berm and foreshore. The eastern research area (ERA) extends from the eastern boundary of the Lianli Island Bridge to the vicinity of Haiyang Harbor, encompassing Fengxiang Beach and Wanmi Beach. This segment of beach, known for its sand sculpture construction and beach tourism, experiences a considerable amount of human activity.

The point cloud data from three segments of beach were imported into Arcgis online trial version. Subsequently, elevation grid (DEM) data for each segment of beach across different years were generated from these point clouds. Volume differences, which represent beach erosion or siltation (with negative values indicating erosion and positive values indicating siltation), were calculated by comparing DEMs from adjacent years using ArcGIS’s spatial analysis tool. This approach allowed us to determine volume changes within the same shoreline area across consecutive years. By comparing and analyzing the erosion and siltation characteristics of each shoreline profile, areas with significant changes in these processes were identified. Additionally, field measurements of GNSS RTK elevation data for 11 typical profiles were analyzed to assess erosion and siltation patterns along the beach. Profiles P1 to P4 are in the WRA, profiles P5 to P8 in the CRA, and profiles P9 to P11 in the ERA. Through quantitative calculations and qualitative analysis, the changes in erosion and sedimentation of different coastal sections in the beach study area are assessed. Considering the impact of human activities on different coastal sections, the study examines the response of beach erosion and sedimentation to human activities. Therefore, this study can provide support for decision-makers in the relevant areas in terms of beach protection and sustainable development.

3. Results

3.1. Characterization of Erosion Volume and Analysis of Changes

Figure 4 illustrates the variation in beach volume over multiple years within the ERA. As indicated in

Table 1. Erosion and siltation between years.

Research Area		Years
		2017–2018	2018–2019	2019–2020	2020–2021	2021–2023
ERA	Siltation volume/m3	19,297.91	23,480.21	20,858.27	11,165.75	35,859.02
	Erosion volume/m3	−22,363.43	−17,217.63	−19,735.92	−28,100.01	−54,963.62
	Overall volume/m3	−3065.52	6262.58	1122.36	−16,934.26	−19,104.60
CRA	Siltation volume/m3	136,084.03	115,094.07	142,376.65	69,576.50	174,506.16
	Erosion volume/m3	−31,292.22	−84,538.04	−64,778.71	−85,484.39	−142,519.60
	Overall volume/m3	104,791.81	30,556.03	77,597.94	−15,907.89	31,986.56
WRA	Siltation volume/m3	56,812.11	44,148.70	74,502.40	17,004.33	67,846.55
	Erosion volume/m3	−13,586.07	−59,348.57	−11,771.41	−50,757.33	−29,784.92
	Overall volume/m3	43,226.04	−15,199.87	62,730.98	−33,753.00	38,061.63
Overall Study Area	Overall volume/m3	144,952.33	21,618.74	141,451.28	−66,595.15	50,943.59

, both erosion and siltation occurred in the ERA during the periods of 2017–2018, 2018–2019, and 2019–2020, demonstrating a rough balance between these two processes. During the years 2017–2018, the beaches in the study area experienced slight erosion, with a total erosion volume of 3065.52 m³. In the subsequent periods, 2018–2019 and 2019–2020, slight siltation was observed, with siltation volumes of 6262.58 m³ and 1122.36 m³, respectively. The backshore of Fengxiang Beach exhibits localized siltation, primarily attributed to beach nourishment in areas where numerous sand sculptures are situated. In contrast, the periods of 2020–2021 and 2021–2023 were characterized by significant erosion, with volumes of 16,934.26 m³ and 19,104.60 m³, respectively. Notably, foreshore erosion at both Fengxiang Beach and Wanmi Beach is particularly pronounced. The phenomenon of localized siltation appeared on the beach in certain years, caused by the annual sand replenishment for sand sculpture construction on the foreshore of Fengxiang Beach.

Over time, the CRA has predominantly experienced siltation, with the exception of erosion that occurred from 2020 to 2021. The processes of erosion and siltation are distributed in a staggered pattern across various profiles of the beach (Figure 5). Significant siltation has been observed near Yangjiao Bay, a phenomenon linked to the transport and deposition of silt carried by the river near Yangjiao Bay, resulting in substantial sediment accumulation. In contrast, notable erosion is evident along the beach foreshore of the CRA, particularly in regions farther from Yangjiao Bay. Spatially, the beaches of the CRA generally exhibit a sequential pattern of erosion followed by siltation, and then further erosion, progressing from east to west.

The WRA exhibits a staggered distribution of erosion and siltation along the coastline. In this region, depositional and erosional patterns demonstrate interannual variability (Figure 6). Erosion was observed on the beach foreshore from 2017 to 2018, while siltation was particularly pronounced on the backshore. Significant strip erosion occurred on the beach foreshore between 2018 and 2019. The beach experienced a siltation event during 2019–2020, primarily affecting the foreshore, with a total siltation volume of 62,730.984 m³. In the following year, 2020–2021, both erosion and siltation were recorded, resulting in a net erosion of 33,752.999 m³. From 2021 to 2023, the beach exhibited slight overall siltation. Field surveys indicate that the backshore of the WRA is adjacent to extensive beach-farming activities, where farmers actively engage in beach nourishment to safeguard their farming facilities. Furthermore, they partake in sand mining on the foreshore and conduct beach nourishment on the backshore, contributing to the alternating patterns of erosion and siltation.

The characteristics of erosion and siltation across the three profiles of the beach demonstrated significant variation over the years. The foreshore of the ERA exhibits a pattern of siltation, followed by weak erosion, and then erosion. In contrast, the CRA shows a pattern of siltation, weak erosion, and again siltation. Meanwhile, the ERA exhibits variations characterized by weak siltation, weak erosion, and siltation. These findings indicate substantial variability in the factors and mechanisms influencing erosion and siltation among the three beach research areas.

Table 1 illustrates the inter-annual variation in beach erosion and siltation across different research areas. The beach in the ERA has predominantly experienced erosion over the years, with only weak siltation occurring in some years. In contrast, the beach in the WRA exhibits an alternating pattern of siltation and erosion. The CRA, however, predominantly experiences siltation, with volumes significantly exceeding the total erosion observed in both the eastern and western research areas combined. Consequently, the overall research area demonstrates a greater prevalence of siltation compared to erosion.

Table 2. Area of erosion and siltation between years.

Research Area		Years
		2017–2018	2018–2019	2019–2020	2020–2021	2021–2023
ERA	Siltation area/km2	0.1717	0.1749	0.1599	0.0541	0.1429
	Erosion area/km2	0.1300	0.1100	0.1050	0.2114	0.1401
CRA	Siltation area/km2	0.4249	0.3724	0.4646	0.2887	0.3682
	Erosion area/km2	0.1180	0.3733	0.2375	0.4132	0.3762
WRA	Siltation area/km2	0.3086	0.2084	0.3516	0.1370	0.3227
	Erosion area/km2	0.1249	0.2523	0.0990	0.3138	0.1370
Overall Study Area	Siltation area/km2	0.9052	0.7557	0.9761	0.4798	0.8338
	Erosion area/km2	0.3729	0.7356	0.4415	0.9384	0.6533

illustrates the areas impacted by erosion and siltation within the research area. Erosion was most pronounced during 2020–2021, reaching multi-year maximums in both volume (66,595.152 m³) and area (9384 m²), with all three segments of the beach research area experiencing erosion during this timeframe. Notably, the 2017–2018 period recorded the most significant siltation, primarily attributed to excessive siltation in the CRA.

3.2. Characteristics of Inter-Annual Variability in Typical Profiles

Figure 7 illustrates the annual variation of typical profiles across different research areas. Four profiles, designated P1 to P4, were established in the western beach region. The backshore of profile P1 exhibited relative stability from 2016 to 2020; however, it underwent significant changes in 2021 and 2022. In 2021, the backshore began to experience substantial erosion, followed by notable siltation in 2022, which was accompanied by a forward shift of the beach berm and an increase in elevation at the top of the beach berm. Since 2017, significant siltation has been observed on the foreshore, with the most pronounced siltation occurring in 2022. In contrast, the inner foreshore area has remained relatively stable. On-site investigations suggest that the primary reason for this stability is the artificial piling of sand by local farmers behind the backshore, aimed at elevating the backshore and beach berm to protect their aquaculture facilities from damage caused by wind waves. Profile P2, in contrast, exhibits considerable variations in the backshore and foreshore from year to year, unlike the relative stability observed in the inner shore. Severe downward erosion of both the backshore and foreshore, along with damage to the beach berm, was recorded between 2016 and 2017. A gradual restoration of the backshore and beach berm occurred from 2018 to 2021. However, significant erosion was noted in both the beach berm and foreshore in 2022. Profiles P3 and P4 generally maintained relative stability from 2016 to 2022, although the foreshore of profile P4 experienced slight siltation. Overall, the four profiles in the WRA show weak change; nevertheless, there is an observable erosive trend at the beach foreshore and siltation at the backshore, which is associated with sand mining activities at the foreshore and beach nourishment at the backshore.

Four profiles (P5 to P8) were established in the CRA. The foreshore and backshore of profile P5 demonstrate a trend of increasing erosion, with particularly severe foreshore erosion observed in 2022, resulting in a backward shift of the beach berm. The foreshore and backshore of profile P6 exhibit significant variability. From 2016 to 2022, the foreshore was predominantly affected by siltation, with an especially pronounced siltation occurring from 2020 to 2022. A noticeable trend towards increased seaward siltation is evident, although the inner foreshore remains relatively stable. Profile P7 indicates a more stable trend characterized by gradual siltation, with the beach berm shifting forward each year, reflecting the positive influence of estuarine sediment recharge in the area. Conversely, profile P8 exhibits a trend of annual erosion, resulting in a gradual retreat of the foreshore and beach berm, particularly evident in 2022. Profiles P6 and P7, located in the CRA near Yangjiao Bay, show a clear trend of seaward siltation year after year. In contrast, Profiles P5 and P8, situated farther from Yangjiao Bay, indicate a trend of backward erosion.

Three profiles (P9 to P11) were established in the ERA. The foreshore and inner foreshore of profile P9 generally exhibit a trend of erosion year after year, with notable forward and backward movements of the beach berm observed in both 2017 and 2022. However, in 2022, there was also siltation on the backshore, primarily due to beach nourishment efforts for the construction of sand sculptures. The characteristics of profile P10 indicate a clear trend of erosion in all years except 2021, with particularly severe erosion recorded in 2022. From 2016 to 2022, the backshore of profile P11 has remained relatively stable, while the beach berm has shown a slight elevation. In 2022, the height of the beach berm increased significantly, and the beach slope has become slightly steeper each year, with the inner foreshore experiencing annual erosion. Although all three profiles in the ERA demonstrate a consistent trend of erosion over the years, there are instances where the backshore and beach berm suddenly increase in height. The ERA is well-developed for tourism, featuring numerous facilities along the rear beach. To protect these facilities from potential damage, sand accumulation work is performed on the backshore, resulting in an elevation of the backshore.

4. Discussion

The erosion and sedimentation observed in the WRA are closely related to beach aquaculture activities in the backshore area. High-intensity beach aquaculture involves sand excavation and the construction of numerous drainage pipes on the beach, which disrupts the equilibrium of the beach and contributes to erosion. Erosion in the WRA is primarily attributed to farming activities on the adjacent backshore. Farmers periodically remove sand from the foreshore and deposit it on the beach berm, further disrupting the sediment balance and exacerbating localized beach erosion. In addition, aquaculture farmers regularly replenish the sand on the western section of the beach in the study area. As a result, the western beach study area experienced a slight accumulation of sediment on a large scale between 2019–2020 and 2021–2023.

In 2019, Typhoon Lekima made landfall along the southern coast of Shandong Province, severely affecting the coastal beaches of Haiyang and causing significant erosion, with a total beach erosion volume estimated at approximately 2.43 × 10⁴ m³ [55]. The typhoon primarily impacted the WRA, which exhibited erosion in 2019 compared to 2018. Following the passage of the typhoon, the beach’s self-restoration capabilities facilitated sedimentation between 2019 and 2020, gradually restoring the beach to a balanced state.

There is significant annual variation in siltation and erosion in the CRA, which can be attributed to sediment transported by the nearby river at Yangjiao Bay and deposited in the estuary, as well as anthropogenic disturbances. In recent years, the foreshore area of the beach on the western side of Yangjiao Bay has experienced continuous cycles of erosion, siltation, and subsequent erosion. Haiyang Beach underwent extensive erosion, followed by a gradual recovery after Typhoon Likima impacted the coast of Southeastern Shandong in 2019. However, the removal of several aquaculture ponds and the restoration of certain sandy beaches adjacent to the estuary has led to the formation of a significant siltation area on the foreshore of the western side of the estuary by 2023.

The sediment on the beach of the study area primarily originates from Dingzi Bay and the Dongcun River near Yangjiao Bay, and it is transported from west to east by waves and tidal currents. At the estuary, the Dongcun River introduces sediment into the sea, where the flow velocity decreases due to the expansion of the water flow and the increase in water volume in the estuarine area. This reduction in flow velocity diminishes the river’s capacity to carry sediment, resulting in sedimentation at the estuary. Furthermore, following the construction of Lianli Island, the wave shadow effect has modified the original west-to-east direction of sand transport, redirecting it to align with the coastline behind the island (Figure 8). Consequently, a significant amount of sediment accumulates in the shoreline section extending from near Yangjiao Bay to the Lianli Island Bridge. Acting as a natural barrier, Lianli Island effectively shields the beach from the direct impact of wind waves. As a result of the interplay of these various factors, substantial sedimentation has occurred near Yangjiao Bay in the CRA.

The construction of Lianli Island has resulted in sediment accumulation on the west side of the Lianli Island Bridge, leading to the formation of a sand spit. Fengxiang Beach, extending from Yangjiao Bay to the Lianli Island Bridge, primarily serves as a venue for beach volleyball competitions. To meet competition requirements, individuals often extract sand from the foreshore and the sand spit to artificially replenish the backshore, which has contributed to the underdevelopment of the sand spit. Consequently, the beach on the east side of Yangjiao Bay is experiencing foreshore erosion and backshore silting.

The ERA has exhibited significant erosion characteristics over the years. This area is situated at the terminus of the west-to-east longshore sediment transport, where the sand source has diminished. The reduction in sand sources, combined with alterations in the direction of regional coastal sand transport following the construction of Lianli Island, has resulted in a year-on-year decrease in incoming sand to the ERA. Consequently, this has accelerated erosion in the region. The western side of Fengxiang Beach, adjacent to the Lianli Island Bridge, experiences a local sediment transport direction influenced by the construction of Lianli Island, shifting from east to west. In contrast, the sediment transport direction on the eastern side of Fengxiang Beach continues to flow from west to east. As a result, the eastern side of Fengxiang Beach is subjected to more severe erosion. The WBB, located to the east of ERA, experienced further erosion in 2023. The foreshore is generally in a state of erosion, with the width of the dry beach decreasing annually. On the beaches of the ERA, erosion has resulted in the formation of beach scarps, characterized by steeper slopes which have led to the collapse of coastal structures. Additionally, the slope of the P11 profile has exhibited increasing steepening over the years. Despite the implementation of recent ecological protection and restoration projects along Wanmi Beach, particularly in Yangjiao Bay and the beach tourism zone, the trend of erosion continues to intensify. These initiatives have included the restoration of 15 km of sandy shores and 12.67 hectares of coastal wetlands. Plans for further restoration in 2024 involve the replenishment of 4.7 km of sandy shores and the addition of 259,000 cubic meters of sand. However, these efforts have proven inadequate to reverse the escalating erosion. The numerical simulations concluded that the presence of Lianli Island can protect the sandy coast to its north from severe erosion by wind and waves, thereby preventing the retreat of the coastline based on the sea area use demonstration report of the Lianli Island [56]. Additionally, Lianli Island can reduce the amount of sand brought into the shallow area due to coastal collapses. However, contrary to the predicted results, the beach in the ERA mainly exhibits a large area of slight erosion based on the above analysis of multi-year beach elevation measurement results by UAV and RTK. This indicates that the sand-blocking effect of Lianli Island and the sand loss caused by human activities have a greater impact than the protective effect of the island.

The beaches in different research areas exhibit significant considerable variability in the spatial distribution of erosion and siltation, primarily due to a range of human activities. These activities have modified the local sediment transport direction, thereby influencing sediment deposition and erosion patterns within Yangjiao Bay as well as the erosion and siltation processes on neighboring beaches. Additionally, human alterations to the backshore and beach berm have disrupted the natural equilibrium of the beach.

In addition to the notable sedimentation observed on the beach near Yangjiao Bay in the CRA, the overall beach is primarily characterized by erosion in the absence of artificial sand replenishment. To protect the beach from further erosion, it is essential to implement maintenance and repair measures. The scope of beach farming activities in the western study area is excessively large, with some aquaculture ponds directly constructed on the beach or foreshore, and numerous water pipes exposed and arranged on the beach surface. Sediment replenishment should be conducted in this section of the beach, and the exposed drainage culverts should be buried and modified to mitigate their impact on the beach surface. Additionally, the direct extraction of sand from the beach should be prohibited to protect the beach shoulder aquaculture facilities. It is recommended that measures be implemented to cease beach aquaculture in areas severely affected by erosion and to facilitate the restoration of the beach.

The presence of Lianli Island and the Lianli Island Bridge in the Coastal Research Area (CRA) has led to changes in the sediment transport dynamics of certain silt and sand deposits. A sand spit has formed at the base of the Lianli Island Bridge. Currently, sand is being extracted from this sand spit to replenish the adjacent Fengxiang Beach and the WBB, both of which are experiencing erosion. The sand replenishment plan for the regional beach is developed from both plan and profile perspectives, considering local wave energy conditions and beach topography to evaluate the feasibility of the plan and identify appropriate sand dumping locations. Historically, numerous countries and regions have also addressed the risks associated with beach erosion through beach nourishment strategies.

5. Conclusions

This paper focuses on Wanmi Beach in Haiyang City, Yantai, Shandong Province, as the subject of research. By analyzing data collected from field surveys, this study conducts a quantitative analysis of the erosion that has occurred at Wanmi Beach over the past eight years aiming to assess both beach erosion and sedimentation. Based on these findings, several conclusions were as follows.

Since 2017, the eastern, central, and western research areas (ERA, CRA, and WRA) have exhibited complex patterns of erosion and siltation. The trend of erosion in the ERA has been increasing annually, particularly along the beach foreshore. In the CRA, erosion and siltation occur intermittently, with a notable transition from siltation to erosion and back to siltation, where Yangjiao Bay serves as the primary site of siltation. The WRA alternates annually between erosion and siltation. Notably, during the period from 2019 to 2020, this area experienced extensive siltation, accumulating a total volume of 62,730.98 m³. This phenomenon is associated with the removal of beach aquaculture and beach restoration efforts on the western side of the CRA.

A comparative analysis of beach profiles over the years indicates that profiles P1 to P4 in the WRA exhibit relative stability, characterized by both erosion and siltation. In recent years, within the western study area, four typical profiles have shown deposition on the upper intertidal beach surface and erosion on the lower portion. Profiles P6 and P7 in the CRA, located near Yangjiao Bay, remain stable and silted, while profiles P5 and P8, situated further from Yangjiao Bay, undergo significant and continuous erosion. The three profiles in the ERA demonstrate weak erosion, occurring only in select years. The observed patterns of change in the beach profiles correspond with the results of beach volume changes.

Erosion in the western beach survey area has been significantly influenced by farming activities in the adjacent backshore region. Aquaculture operators have disrupted the natural balance of the beach by elevating the beach berm to protect their facilities, extracting sand, and constructing culverts and pipes. The construction of Lianli Island has notably impacted the central study area, altering the direction of sediment transport to some extent. Sediment accumulates in the section near Yangjiao Bay, which has remained silted over the years. However, foreshore erosion is particularly pronounced at the ends of the study area, far from Yangjiao Bay, due to extreme weather and human activities. Over the years, there has been a persistent erosion of the ERA, attributed to the reduction of the sand source and the construction of Lian Li Island, which has modified the direction of sand transport. This has resulted in a year-on-year decrease in incoming sand and accelerated erosion. This has led to a yearly decrease in sand supply. Moreover, the booming tourism and overdevelopment of the beach in the ERA have resulted in a significant loss of beach sand. Consequently, there has been a growing trend of erosion at Fengxiang Beach and along the WBB. This is slightly different from the predicted results in the marine area use argumentation report for the Lianli Island (artificial island) project in Haiyang.