I'm from Sanshui, and I want to know how to calculate the tides in Beijiang River here.

Chu Chiang Delta

Formerly known as Yuejiang Plain. Located in the eastern coast of Guangdong Province, China, it is a delta complex with a radial estuary, which is the general name of the large delta formed by the simultaneous alluvial of Xijiang River and Beijiang River and the small delta formed by the alluvial of Dongjiang River. It is an inverted triangle, with the bottom line starting from Sanshui City in the west, Guangzhou City in the east, and Shilong, with the apex at Yamenwan. The area is about 1. 1 10,000 square kilometers. Alluvium is thin, generally 20 ~ 30 meters. The ground fluctuates greatly, surrounded by hills, mountains and islands, accounting for 30% of the area. The central part is plain, distributed in southern Guangzhou, northern Zhongshan, eastern Jiangmen and western Humen. The annual sediment transport capacity of the Pearl River system is more than 80 million tons, and the delta near the estuary is still extending to the South China Sea. In the estuary area, it can stretch 10 ~ 120 meters every year, which is one of the key reclamation areas in China. The delta has a subtropical climate, which is warm and humid all year round. The annual average temperature is 2 1 ~ 23℃, the coldest 1 monthly average temperature 13 ~ 15℃, and the hottest July average temperature is above 28℃. There are frequent typhoons from June to 10, with concentrated rainfall and the hottest weather. The annual average precipitation exceeds1500mm. The rainy season is synchronized with the high temperature season, with fertile soil and rivers, which is beneficial to agriculture. The yield per unit area of rice is among the best in China. Tropical and subtropical fruits include litchi, citrus, banana, pineapple, longan, carambola, mango, grapefruit and lemon. Three-dimensional agricultural structures such as mulberry-based fish ponds, fruit-based fish ponds and sugarcane-based fish ponds have been developed, which has become a model of ecological agriculture in China. There are sugar, silk, food, paper, machinery, chemicals, building materials, shipbuilding and other industries, known as the pearl of the South China Sea.

Ecological characteristics

Biomass and composition (mg/L) of phytoplankton in the Pearl River Delta: total phytoplankton is 65,438 0.63, diatom is 87.4%, green algae is 4.9%, cyanobacteria is 65,438 0.9%, dinoflagellate is 65,438 0.5%, Chrysophyta is 0.4% and Euglena is 7.8%.

Species composition of zooplankton: protozoa (species) 34, rotifer (species) 38, cladocera (species) 26 and copepod (species) 49, with a total of (species) 147.

Number and biomass of zoobenthos: 198 1 year (individual/m2) 249.1.1981year (g /m2) 29.654,1988.

Main economic fish: bream, silver carp, silver carp, silver carp, eel, flower eel, herring, grass carp, mandarin fish, red-eyed trout, Hainan red squid and bigeye squid.

Physical and geographical characteristics of the Pearl River Delta

The Pearl River Delta is a tropical delta, because its geographical location is south of the Tropic of Cancer (for a small delta), and for a large delta, it is also between 23 40 ′-265 438+0 30 ′ north latitude, that is, most of it belongs to the tropical range. From the climate point of view, the big delta also belongs to the tropical region (see Zhu Kezhen et al. Phenology, 1962). Landform development also has this feature, and the vegetation landscape is more influenced by it, developing into tropical monsoon rainforest vegetation. Moreover, because the northern part of the delta is the mountainous area of northern Guangdong, it plays a barrier role to the cold current from the north, so that tropical vegetation can invade the mountainous area north of the Tropic of Cancer along the valley.

The Pearl River Delta region includes Guangzhou, Shenzhen, Zhuhai, Foshan, Jiangmen, Zhongshan, Dongguan and Huicheng, Huiyang, Huidong and Boluo in Huizhou, and Ruizhou, Dinghu, Gaoyao and Sihui in Zhaoqing. The whole area accounts for 23.4% of the total area of the province, and the population accounts for 31.4% of the total population of the province (1.994). In recent years, GDP has accounted for about 70% of the province's GDP. The Pearl River Delta is one of the fastest growing areas in China. With the rapid development of economy, the social development in this area presents the characteristics of high degree of rural industrialization and rapid process of urban-rural integration.

Seen from the topographic boundary of the Pearl River Delta, Luoping Mountain Range is the dividing line between the west and the north, that is, the Xijiang River valley area is west of Luoping Mountain Range, which is customarily called the western mountainous area of Guangdong. To the north of the mountain range is the Beijiang River system, or the mountainous area of northern Guangdong. Luofushan area in the east is the eastern boundary of the delta.

(1) landform features

The tropical characteristics of the Pearl River Delta are reflected in the river network, with large water volume, small sediment concentration, many radial branches and wide and deep waterways. However, because the development history began after the Middle Pleistocene, the subsidence is not large, so the biggest difference between it and the Yangtze River and Yellow River Delta is that its formation history is short, its sedimentary thickness is small, and its speed of advancing to the bay is fast. The Pearl River Delta is formed by silting on many rivers in Gully Bay, so it is called a composite delta. For example, Guangzhou is known as the "Three Rivers Summary". But the area is not large, and the development potential is not as good as that of the Yangtze River Delta.

The formation of Shui Gu Bay in Guangzhou was caused by the depression between Yunfu Uplift in Guangning and Huiyang Uplift in Heyuan under the influence of the Pacific Ocean and Indian Plate. In Mesozoic, there were red basins such as Sanshui, Gui Long, Dongguan and Xinhui in the depression. Surrounded by hills formed by Paleozoic strata. It was invaded by Mesozoic granite and volcanic rocks (such as Xiqiao Mountain, a tertiary ancient volcano). After leveling at the end of Tertiary, it rose in Quaternary, that is, the quasi-plane of 1000m around the delta today. For example, at the top of Beiluoshan Mountain in Qingyuan, the hilly landform is gentle, called 12 hill, which is a good base for off-season crops. The main peaks of Luoping Mountain are mostly around 1 1,000m, such as Jilong Mountain in Gaoyao (1 1,000m), Luoda Mountain in Qingyuan (1 1,024m), Apo Mountain in Fogang (1 1,24m) and Qingyun Mountain in Xinfeng (/). The decline of the Pearl River Delta has made it a low-lying hilly and terraced area. Quaternary transgression, continental shelf descent and continental rise, so Quaternary terraces tend to tilt into the sea, which makes the basement of Shui Gu Bay have buried terraces. Delta deposition began after the Middle Pleistocene (about 40,000 years), and the hilly platform exposed to the sea became the hills on the delta plain, and the valley landforms with the causes of "Danxia landform" and "Shimen" formed at the exposed bedrock. Platforms or terraces can reach 5 levels, with a large distribution area. The plain sediments also thickened to the sea, increasing from 25m to 60m, and the maximum thickness was 63.6m in the Quaternary in Denglongsha, including marine layer 2 and continental layer 1, indicating that there were two periods in the delta.

The development of the delta plain towards the sea can be divided into the following three stages:

1. During the formation of the delta in the lower reaches of each river, the Xijiang River is outside the mouth of Sanrong Gorge, and the river bifurcates, entering Beijiang River in the northeast and Gaoming River in the south. It was not until the Song Dynasty that it silted up into the Antelope Gorge. After leaving Damiao Gorge, Beijiang River diverges radially and forms a delta in the lower reaches of Beijiang River. Today, Beijiang River is still dry. Dongjiang branch into the lower reaches of Dongjiang River after leaving Luo Tian Gorge (Boluo Cave). At that time, the deltas were not connected. There are also the development of the downstream small deltas such as Zengjiang, Suijiang and Tanjiang, which were also formed in prehistoric times.

2. The composite delta was formed at the beginning of the historical era, and the deltas in the lower reaches of the river began to unite. For example, the newly formed delta in the lower reaches of Xijiang River and Beijiang River is the product of the cooperation between Xijiang River and Beijiang River. The downstream delta of Dongjiang River developed, and a new delta was formed downstream, which was also deposited in cooperation with Zengjiang River. Today, the compound triangle is formed in this period. In addition to the delta plain, there is also a "just-in-time plain" deposited on the sea surface, which is different from the flood plain on both sides of the river. First, the river channel is a two-way tidal channel; Second, there is no false terrace landform with high and low bank water levels; Third, the plain is not inclined, and the river is curved, which is the main tourist scenic resource in the delta and has high development value. For example, the famous "Litchi Bay" has become one of the eight scenic spots in Yangcheng in the Ming Dynasty. Today is the main agricultural area, called "reclamation area".

3. After the Tang and Song Dynasties, the main river roads mostly passed through Koushan in the front of the delta. Outside the entrance, the river diverges radially, forming a new delta. For example, Jiangmen River passes through Jiangmen hilly area and forms a delta in Xinhui, which is called Xinhui thrust delta. Xijiang trunk line passes through Ganzhutan hilly area, that is, Zhongshan thrust delta accumulates in Zhongshan city; After passing through the city abutment and Shunde hills, the main road of Beijiang River accumulates into Panyu thrust delta in Panyu County. Xijiang trunk highway passes through Zhou Mu hills and rockfill hills in Doumen County, forming Doumen thrust delta. That is, the area called "Shatian District" today is one of the rice production bases in China. It is also the main large-scale reclamation area in China. There are 6,543.8+0.2 million mu of mudflats with silt as shallow as -3 meters outside Bamen. The shoal within 1 m reaches 400,000 mu, the coastline advances by 60-150m annually, and the annual siltation height is10-20cm.

The landform of hilly platform is old; So most of the weathering crust has developed into lateritic red soil, which belongs to lateritic red soil. Only the higher hills can see the development of red soil, which is beneficial to the growth of tropical monsoon rain forest.

(b) coastline changes

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 zengtian counties and cities. The coastline extends all the way to the seaside. The delta was formed in the Atlantic period about 6000 years ago. The coastline at that time can be determined by the coastal topography at the foot of hills and slopes in the delta, such as sea cliffs, sea caves, sea terraces and sand dikes. Today, these coastal landforms can be seen at the foot of the hills in the delta plain, such as the Qixinggang Cliff and the sea erosion platform in Guangzhou. Therefore, the coastline of Shui Gu Bay can be basically determined by the contact line between hills and plains. Delta began to develop at the front of these coastal landforms, such as the plain in the lower reaches of Xijiang River, and extended to Guangli, because the time when the Neolithic site was buried in Beiqiu of Shell Island and Qulinbu was 7 170 140, while the pottery piece was 5680 284 (thermoluminescence), and the Beiqiu of Boluo Hulu Mountain was also on the plain, indicating that the delta in the lower reaches of the river had 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 Neolithic sites, Neolithic sites can basically be used as the coastline of Dongjiang Delta. Because there are no stone islands in the middle of the Dongjiang Delta, most of them are still on the sea, so the Dongjiang Delta is surrounded by the Neolithic coastline of 4,000 years. The top of the northwest river delta has also begun to take shape, because the fence site of Jinlimaogang water trunk line is 4 140 90 (measured by C 14) and the rotten wood layer is 3970110 (Geomorphology Room of South China Normal University,/kloc-0) 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 down to nave (there was Tang Ying Temple in Han Dynasty), and the south was still a sea area. The northwest river delta extends northeast to the north of the South China Sea Waterway (namely the East China Sea Waterway). Because of the discovery of Han Dynasty pottery pieces and other cultural relics 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.

/kloc-On the coastline 0/000 years ago (Tang Dynasty), Dongjiang had reached the downtown area of Dongguan, that is, the top of Dongjiang Delta had developed. But most of them are still pearl ponds. The top of Panyu thrust delta has developed, because "Guangzhou is 70 miles south to the sea" in Yuanhe County Records, indicating that this land is between Shawan and Shunde. The top of Zhongshan thrust delta has also developed, because Huang Chao has troops in today's Rongqi, Guizhou and Ma Qi, so it can be seen that the nearby area has become the hometown of big paddy 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 has been recorded (1233); Zhongshan coastline is on the first line of Henglan, Fu Wei (now named Fusha), Huangpu and Tanzhou (according to records); Near Xinhui, the Song Dynasty has become a tidal field, and ritual music has become a sand in the open sea. During this period, 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. Turning tidal fields into flat land also has 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 the alluvial delta accelerated sand deposition. 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 is not as convenient as going to Dongguan. This shows that in the Southern Song Dynasty, the Zhongshan thrust delta has been extended to Shi Qi and ports, that is, 16 sands in the East China Sea and 18 sands in the West China Sea have been formed. Panyu thrust delta has reached Xiahengli (Sha Yi), and Hongqi Likoumen has begun to take shape. Xinhui thrust the delta to Jiuzisha in the southern margin, and the coastline moved from Li Le to Xiongzishan (Xiongzhou). Most of the Dongjiang Delta was formed in the late Song Dynasty. In the late 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 artificially influenced. Unlike the Song Dynasty, the Ming Dynasty did not build dikes to protect fields, but built dikes into fields and planted reeds and grass on the beach to promote siltation. The top of Doumen Delta has begun to develop, that is, the big Aosha has been formed, and Zhou Mu and Sanjiangkou have also risen. Yellow cloth sand has been formed, and it only enters the southern islands of Zhuzhou and Fenzhou.

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 drive sand, and the east and west sides of Denglangsha were used; Xinhui will go to the Yinzhou Lake in the west of Sanjiang River, and the coastline of Panyu will fill up the Wuzhuyang Ocean, with thousands of hectares of sand reaching ten surges. Dongjiang is progressing slowly, because the lion ocean tide is very strong.

In short, the coastline of the Pearl River Delta is constantly moving towards the sea, with periods of fast and slow. Natural factors are related to the fluctuation of sea level. At high sea level, the coastline advances slowly, but it is faster at low sea level. Man-made factors are dike construction, such as dike protection in Song Dynasty, which accelerated the sedimentation in Shatian downstream, and planting reed mud in Ming Dynasty, which accelerated the sedimentation. Tidal action and upstream sediment and water also have influence, such as slow sedimentation in Humen and Yamen waterways, which is the reason for strong tidal current. In the delta area between Humen and Yamen, siltation is strengthened.

(3) Tropical climate

The tropical climate in the Pearl River Delta is characterized by four unknown seasons, no snow in three winters, evergreen trees, evergreen fields and no frost. Zhu Kezhen said in his book "Special Climatology" that the tropics are places where "all seasons are summer, and it rains in autumn". He thinks that the south of Wuling Mountain is in the tropics. Therefore, the Pearl River Delta belongs to the tropical region.

The main reason for the formation of tropical climate is the influence of geographical latitude. The Tropic of Cancer is the dividing line between tropics and subtropics. Most of the Pearl River Delta is south of the Tropic of Cancer, which means most of it belongs to the tropics. Here the summer solstice sun shines on the zenith, which was called the "North Gate" in ancient times, that is, the sun can shine into the house from the north. The sun is still high in winter, so the delta is still very hot. But the tropical environment here is different from other parts of the world, because of the influence of monsoon, the north wind blows in winter and the south wind blows in summer. In winter, the cold current in the north can also blow into the delta, which will hurt tropical crops, such as litchi, papaya, pineapple and mango. In the delta, the zenith is sunny in summer solstice, and the sun angle often reaches 87, and it also reaches 43 in winter solstice. The daytime is 14 hour (summer solstice), the winter solstice is still 1 1 hour, and the sunshine hours are 1.900-2200 hours for several years. The annual average total solar radiation is 454 1.6 MJ/m2 in Zhongshan and 5404.9 MJ/m2 in Shenzhen, taking the annual average. Guangzhou 1 monthly average temperature 13.3℃ in winter, and the days below 5℃ are only three days, so the Pearl River Delta can only be said to be "winter weather", not "winter climate". The high temperature days in Guangzhou are only 6 days (> 35℃), which reflects the characteristics of maritime climate, that is, there is no high temperature in summer, which is different from the subtropical Yangtze River Delta climate.

The delta is flat, and the rainfall is less than the surrounding hills, with an average of about 1600 mm, and the periphery can reach 2000-2600 mm The rainfall is concentrated in summer and less in winter. This rainy season and dry season are the characteristics of tropical climate, which is different from the equatorial belt with high temperature and rainy all the year round. Therefore, equatorial crops such as rubber tree, coconut, betel nut, cocoa, pepper and durian cannot be introduced into the Pearl River Delta, and only tropical crops such as drought-tolerant sisal, mango, pineapple and citronella can be introduced. Rainy weather caused by static front in spring, and long-term rainy weather will lead to grass rot in the early stage. Thunderstorms are dominant in summer, similar to the equatorial belt. It rains for 2-3 hours every afternoon, which is one of the highest rainfall peaks in the year. There are many rainstorms in summer and autumn, which are not destructive in the delta region. Because the surrounding hills are protected, it is also helpful for autumn drought, which is also the characteristic of tropical climate, and often forms the second rainfall peak in the delta. In winter, the denatured cold current enters the delta through the East China Sea, and there may be light rain. Because of the strong sunshine, the evaporation is large. For example, the rainfall in Guangzhou is 1600- 1700 mm, but the evaporation is 17 15.5 mm, so it is in the dry season (10-February). Drought will still happen. There are only 1-2 typhoons invading the delta every year, and the duration of 1 typhoon is only four days, but the rainfall they bring can just alleviate the autumn drought. In addition, about 5-6 typhoons affect the delta every year, so drought is generally lighter than flood. If typhoon and cold wave are added, wind, cold, water and drought are all disaster factors in the delta.

When a typhoon enters the country, the most feared thing is the top tide. When the typhoon increased water and the high tide met, it formed the high tide of strong winds and waves, that is, storm surge, which was called "tidal surge" in ancient times and was first seen in "The Record of Ridges" in the Tang Dynasty. The article said: "Before the tide was exhausted, the hurricane made the tide hit again, and then the waves flooded the coast, flooded people's houses, lost crops and indulged boats. In the south, it is called tide. Or once every few decades. " Typhoon can flood and reduce water, and flood and tide can break through seawalls and form disasters. The delta seawall is1.935km long and needs urgent protection. Because the delta is in the tropics, there are many tropical storms, and the mouth of the bay is trumpet-shaped to the southeast, which has become a storm surge-prone area in China. The measured maximum tidal level is greater than 1.8m, which is mostly caused by storm surge. From1848-1949, 100, there were 60 storm surges in the Pearl River Estuary. The flood time is only 4 hours, and the maximum water level increase is 1 meter. If it is supported by the flood peak, it is a disaster. If you think that the waves can climb very high and have a great influence on the seawall, you should pay special attention. Although storm surges are rare, on the first day of July in the first year of Tongzhi (1862), there were storm surges that "the sea suddenly dried up like land" (reducing water) and "the ground was several feet deep" (increasing water), resulting in "more than 80,000 dead bodies" on the river surface of Guangzhou. The storm surge caused by Typhoon No.9 (1September 9, 983) crossed the 2 129 seawall, with a total length of 47 kilometers, flooded 184 mu of fields and 70,000 mu of fish ponds, and lost 6,543.8 billion yuan of materials (boats, grain, fertilizers and cement), resulting in 23 deaths. In recent years, the average annual sea level rise in the Pearl River Delta has reached 2.08 mm, and it is predicted that the storm surge will be more severe in the future than in the past.

Because tropical crops and fruit trees are widely planted in the delta, the cold damage is also great. The average daily temperature of cold current in early spring is lower than 65438 00℃ for 4 consecutive days, and the seedlings can rot; When the temperature is lower than15℃ for more than 5 days, the seedlings die early and resist green easily. In late autumn, the average daily temperature is lower than 20℃ for more than 3 days, that is, the cold dew wind blows up rice pollen, which leads to the reduction of empty grain production; When the temperature is below 5℃ in winter, even tropical crops suffer, which is called "dark frost".

Summer rainfall is caused by fronts, thunderstorms, convective rain, typhoons, etc. Heavy rain (daily rainfall is more than 50 mm) can cause disasters, especially in the combination of the first flood season and the second flood season, connecting "Dragon Boat Water" and "Muxian Water".

Drought is mainly caused by stable high pressure, such as196411-65438+February, which lasts for 43 days, so it is connected with the previous winter drought and early spring drought, resulting in disasters.

In addition, tornadoes can also cause disasters, which people call "Qu Weilong". 1In March of 878, the White Swan Pond started to rise, and 1500 houses were destroyed. Hundreds of people were killed when the boat capsized, and there were not many foggy days. For example, foggy days in Guangzhou average 4.8 days a year, because the temperature in the lower reaches of the delta is very high.

(4) Tropical flora and fauna

There is no equatorial vegetation in the Pearl River Delta, but there are quite a few tropical vegetation. Although today's natural vegetation has disappeared due to artificial reclamation, tropical tree species, such as red-leaved trees and Aquilaria sinensis, can still be found in the "feng shui forest" and "miscellaneous forest" around some villages, indicating that the ancient hilly platform is a tropical monsoon rainforest vegetation distribution area. There are also alocasia alopecuroides and plantains in the valley, and shrubs, vines and herbs under the forest are mainly tropical species, each of which becomes a dominant community. Ficus carica, kapok, Solanum melongena and Platanus acerifolia, which are widely distributed today, are also tropical tree species. There are Kandelia candel and Bruguiera gymnorrhiza in mangrove forests in the Pearl River Estuary. There are sword beans, sweet potatoes, date trees, salt-tolerant plant rats and so on. Shanghai Beach, distributed in Dongguan, Baoan, Shenzhen and Zhuhai, has a number of aerial photographs as high as 55438+0983.

There are more than 500 kinds of deltas, which also reflect the characteristics of tropics. They belong to 130 families and 373 genera (Chen Shupei, 1984), among which pure tropical genera account for 42% and even pantropical genera account for 53%. Tropical genera account for 62% and tropical species account for 56% in Dinghushan area, namely 129 1 species. Among the genera of Luofushan 146, the pantropical genus accounts for 9 1% (Zheng Zhiqing, 1987). Evergreen vegetation in monsoon forest is mostly geomantic forest and miscellaneous forest, mostly secondary, which is mainly tropical flora (Wang Zhuhao, 1982) with a small area. Most of the hills on the platform are evergreen shrubs. Grass slope with tropical elements is prone to soil erosion because it grows on latosol soil layer. Insect-eating plants such as Nepenthes are tropical plants. The ecological characteristics of tropical plants are also fully reflected in common cultivated trees. For example, on banyan trees, roots of boards, roots of air and roots of columns can be seen, which can grow into forests by themselves. Flowering on the old stems can be seen in carambola and pineapple. Annual flowers are found in Prynne and Hibiscus; The leaves of pliers exist in mangoes; Rotting leaves exist in mangoes and lychees; Drip-pointed leaves are found in bodhi trees. The ecological characteristics of these tropical plants are consistent with the distribution area of tropical monsoon rain forest here. Among them, Aquilaria sinensis (Aquilaria sinensis) was widely planted in Dongguan County in the Ming Dynasty and became a famous product in Dongguan, known as "Vientiane". This shows that the Pearl River Delta is a tropical delta. Also, correspondingly, there are also large tropical animals inhabiting the delta region, although they have been hunted down by people today, such as the rhinoceros recorded in the hilly area of Dongguan.

Delta is a water network area, dominated by swamps, depressions and low-lying forests, so it is also home to many typical tropical giant animals, which also reflects the original tropical characteristics of the delta. Such as Asian elephants, Malay crocodiles, peacocks, etc. There are many descriptions in ancient books, even with fossils as evidence. For example, during the Three Kingdoms period, crocodiles were still growing in Guangzhou. Water mirror Nott said: "The giant crocodile is a rare and strange thing, there are thousands of kinds, I can't remember." Today, Pingzhou fishermen also extracted crocodile skulls from the river, indicating that there are crocodiles in Guangzhou. There are also crocodile skeletons unearthed in Shunde and Xinhui. The (Tangxia) 14C of Dalin is 3020 80, and that of Liu Le is 2540 105. There are also records of elephants harming crops in Nanhan, Dongguan. The author once collected the tibia of an elephant in the mud layer of Guxihu District, Guangzhou. The Annals of the South China Sea (Yuan Dynasty) still records the existence of elephants. There are records of Peacock in Kaiping in Jin Dynasty and Xinhui in Tang Dynasty. It can be seen that the Pearl River Delta has been a place where tropical animals are distributed since ancient times, in which ivory is hunted and used as a commodity. The Tang Dynasty's "North Household Record" contains: "The teeth are small and red, comparable to cutting, not inferior to imported ones." Crocodiles are recorded as cannibals and cannibals, which are very different from Chinese alligators in the Yangtze River, and are consistent with porous crocodiles and crocodiles. In today's Nanyang Islands. Elephants are Asian elephants. Today, due to the continuous development of the delta, the increase of population and the destruction of trees, they have been hunted to death.

summary

From the analysis of geographical environment such as landform, climate, hydrology, vegetation and animals, the Pearl River Delta is a tropical delta, which is different from the Yellow River Delta and the Yangtze River Delta. Geomorphology and hydrology show a good water network with many branches and many wide deep-water rivers. The climate is rich in heat and radiation; Vegetation grows vigorously, with many kinds and animals, which is very beneficial to industrial and agricultural production. In terms of types, the Pearl River Delta is similar to tropical deltas such as the Red River Delta and Mekong Delta. In view of the scarcity of tropical areas in China, we should give full play to the tropical characteristics and potential of the Pearl River Delta.