Due to shallow bedrock and large amount of incoming sand, the Pearl River Delta rapidly extends to the sea, making Panyu, Zhuhai and Doumen become counties and cities with increased fields. The coastline extends all the way to the seaside. The delta was formed in the Atlantic period about 6000 years ago. At that time, the coastline could be determined by the coastal topography at the foot of delta hills and slopes, such as sea cliffs, sea caves, sea platforms and sand dikes. Today, these coastal landforms can be seen at the foot of the hills in the delta plain, such as the ocean cliffs and platforms in Qixinggang, Guangzhou. Therefore, the coastline of Shui Gu Bay can be basically determined by the contact line between hills and plains. Delta began to develop in the front of these coastal landforms, such as extending to the plain in the lower reaches of Xijiang River in Guangli, because the age of Neolithic sites buried in Beidao and Qulinbu there is 7 170 140, while the pottery fragments are 5680 284 (thermoluminescence), and Beiqiu in Boluo Hulu Mountain is also on the plain, which indicates that the delta in the lower reaches of the river has developed. According to the distribution of marine diatoms (brackish water species), foraminifera and silt layers, the delta areas in the lower reaches of rivers basically reflect the transgression scope in the Atlantic period, that is, the coastline 6000 years ago reached Qingyuan Basin in the north, Zhaoqing Basin in the west (Zhao Huanting, 1990) and Dabulo Basin and Tonghu Lake in the east.

Judging from the Neolithic sites, the Neolithic sites in Dongjiang Delta can basically be used as coastlines. Because there are no rocky islands in the middle of Dongjiang Delta, most of them are still on the sea, so the neighbor of Dongjiang Delta is the Neolithic coastline of 4000 years. The top of the Northwest River Delta has also begun to take shape, because the site of Shuigan Fenlan in Jinlimaogang is 4 140 90 (measured by C 14) and the rotten wood layer is 3970 1 10 (Geomorphology Room of South China Normal University, 1988). The age of the epiphytic blue clam under the cliff in Shijie, South China Sea is also 4640 280 years old. That is, the northwest river delta reaches the south of Xiqiao Mountain and Foshan Line (the silt of rattan is 3997 190).

Before 2000 (Qin and Han Dynasties), the Dongjiang Delta was formed by the merger of Dongjiang Delta and Zengjiang Delta, extending to the main hall (Tang Ying Temple in Han Dynasty), and the south was still a sea area. Northwest River Delta extends northeast to the north of South China Waterway (namely East China Sea Waterway). As Han Dynasty pottery pieces and other cultural relics have been found in Xingtan, the burial depth is 2m (Feng Jian Village). Freshwater Malay crocodile grows in Liu Le, and its age is 2540 120. Shi Chong is the hometown of Lv Jia, South Vietnam, so it should be a plain nearby. Chencun also became the land of the Han Dynasty.

On the coastline of 1000 years ago (Tang dynasty), Dongjiang has reached Dongguan, that is, the top of Dongjiang Delta has developed. But most of them are still pearl ponds. The top of Panyu thrust delta has been developed, because Yuanhe County Records says that "Guangzhou is 70 miles south to the sea", which shows that this land is between Shawan and Shunde. The top of the Zhongshan thrust delta has also developed, because Huang Chao was stationed in today's Rongqi, Guizhou and Ma Qi, so it can be seen that the nearby area has become the hometown of large rice fields. Xinhui thrust delta also has a top plain, such as Xinhui, which is the seat of the Sui Dynasty, indicating that a large plain had been formed at that time. The strata in the Tang Dynasty mostly covered the strata in the Han Dynasty, and the delta coastline did not advance much during the Millennium of the Han and Tang Dynasties, which may be related to the sea level rise during this period.

700 years ago (at the end of Song Dynasty), the coastline went south to the middle of thrust deltas, and Dongjiang reached the line of Mayong, Dafen and Daojiao (according to genealogy); Panyu has reached the first line of nuclear fish vortex, and Xiqiaoyong recorded it (1233); Zhongshan coastline is on the first line of Henglan, Fu Wei (now Fusha), Huangpu and Tanzhou (according to records); Near Xinhui, the Song Dynasty has become a tidal field, and ritual music has become a distant sea sand. During this period, the Tanjiang River developed rapidly, with Gemini and Huangchong as the first line, which was the result of Zhuji port immigrants pouring into the delta to build dikes in the Song Dynasty. Changing tidal fields into flat land has also had an impact on sea level decline. Jiaowei is a waterway connecting the two rivers.

400 years ago (late Ming Dynasty), due to the dike construction in Song Dynasty, water flowed into the trough, and various erosion deltas accelerated siltation into sand. For example, Zhongshan belonged to Dongguan in the early Song Dynasty and entered Guangzhou in the Southern Song Dynasty. Because Xiangshan and Panyu were three hundred miles across the sea in the Northern Song Dynasty, it was not so convenient to go to Dongguan. This shows that in the Southern Song Dynasty, the Zhongshan thrust delta has extended to Shi Qi and ports, that is, the Sixteen Sands in the East China Sea and the Eighteen Sands in the West Sea have been formed. Panyu thrust delta has reached Xiahengli (Sha Yi), and the gate of Hongqi intersection has taken shape. Xinhui thrust delta extends to Jiuzisha in the southern margin, and the coastline moves from Li Le to Xiongzi Mountain (namely Xiongzhou). Most of the Dongjiang Delta was formed in the late Song Dynasty. At the end of Ming Dynasty, it extended to the east of Zhang Peng, and the south tributary also extended to the north of Houjie. In the Ming dynasty, the acceleration of the delta coastline was also affected by man-made. Instead of building dikes to protect fields as in the Song Dynasty, the Ming Dynasty built dikes into fields and planted reeds and grass on the floodplain to promote siltation. The top of Doumen Delta has begun to develop, that is, the big ao sand has been formed, and Zhou Mu and Sanjiangkou have also risen. Huangbu Dasha has been formed, only entering Zhuzhou and Fenzhou South Island.

100 (late Qing dynasty), the front coastline was further advanced, and the outer edge of the delta was cut off at Doumen, that is, bamboo was used to expel sand, and lanterns were used to sand on the east and west sides; Xinhui will go to the bank of Yinzhou Lake in the west of Sanjiang River, and the coastline of Panyu will be filled with Wuzhuyang Ocean, and thousands of hectares of sand have reached ten surges. Dongjiang is progressing slowly, because the tide in Lion Ocean is very strong.

In short, the coastline of the Pearl River Delta is constantly moving towards the sea, with periods of fast and slow. As far as natural factors are concerned, it is related to the fluctuation of sea level. In the high sea level period, the coastline advances slowly, but it advances rapidly in the low sea level period. Man-made factors are dike construction. For example, dike protection in Song Dynasty accelerated sedimentation in Shatian downstream, and dike construction and planting reed mud accelerated sedimentation in Ming Dynasty. Tidal action and upstream sediments and water also have an impact, such as the slow siltation of Humen and Yamen waterways, which is the reason for the strong tidal current. Between Humen and Yamen