The physical 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 (in the case of small deltas), and in the case of large deltas, it is also between 23°40′-21°30′ north latitude.

That is, most of them belong to the tropical range.

From a climate perspective, the large delta also belongs to the tropical region (see Zhu Kezhen et al., "Phenology", 1962).

The landform development also has this characteristic, and the vegetation landscape is even more affected by it, developing into tropical monsoon rainforest vegetation.

And because the north of the delta is a mountainous area in northern Guangdong, it acts as a barrier to the cold current from the north, allowing tropical vegetation to invade the mountainous areas north of the Tropic of Cancer along the valley.

From the topographic boundary of the Pearl River Delta, the Luoping Mountains are its western and northern boundaries. That is, to the west of the Luoping Mountains is the Xijiang Valley area, which is customarily called the Western Guangdong Mountains; to the north of the mountains is the Beijiang River System, or the Northern Guangdong Mountains.

The Luofu Mountain District on the east side is the eastern boundary of the delta.

(1) Geomorphological characteristics The tropical characteristics of the Pearl River Delta are reflected in the river network, which includes large water volume, low sediment content, many branching and radiating river channels, and the development of wide and deep water channels.

However, because its development history began after the Middle Pleistocene and the amount of subsidence was not large, the biggest difference between it and the Yangtze River and Yellow River deltas is that it has a short formation history, small sediment thickness, and rapid advancement toward the bay.

The Pearl River Delta is formed by sedimentation on multiple river channels in Drown Valley Bay, so it is called a composite delta.

For example, Guangzhou is known as the "Three Rivers Collection".

However, its area is not large, so its development potential is not as good as that of the Yangtze River Delta.

The formation of Drowning Valley Bay in Guangzhou was caused by the formation of a depression between the Guangning Yunfu uplift and the river source Huiyang uplift due to the interaction of the Pacific and Indian plates.

In the Mesozoic Era, red basins such as Sanshui, Longgui, Dongguan and Xinhui were deposited in the depression.

It is surrounded by hills formed by Paleozoic Era strata.

It was also invaded by Mesozoic granite and volcanic rocks (such as Xiqiao Mountain, which is a Tertiary ancient volcano).

After leveling at the end of the Tertiary Period, it rose in the Quaternary Period, which is now the 1,000-meter quasi-plane of the mountains surrounding the delta. For example, the top of Beidaluo Mountain in Qingyuan has a gentle hilly landform, called 12 hills, which is a good base for off-season crops.

The main peaks of the Luoping Mountains are mostly around 1,000 meters, such as Gaoyao Jilong Mountain (1,007 meters), Qingyuan Daluo Mountain (1,024 meters), Fogang Apo Mountain (1,224 meters), Xinfeng Qingyun Mountain (1,246 meters), Lianpingjiu

Lianshan (1279 meters) etc.

Xijiang, Beijiang and Dongjiang are all inherited quasi-plain rivers.

The collapse of the Pearl River Delta turned it into a low, hilly and platform area.

During the Quaternary transgression, the continental shelf descended and the continent rose, so the Quaternary terraces tended to sink toward the sea, resulting in the existence of buried terraces at the base of Drowning Valley Bay.

Delta deposition began after the Middle Pleistocene (approximately 40,000 years ago). The hilly platform protruding from the sea became hillocks on the delta plain, and genetic valley landforms such as "Danxia topography" and "Shimen" were formed where the bedrock was exposed.

Platforms or terraces can reach level 5 and are distributed over a large area.

The plain sediments also thicken toward the sea, from 25 meters to more than 60 meters. The thickest is 63.6 meters of Quaternary sediments at Dengrensha. There are marine layer 2 and continental layer 1, indicating that there are old and new layers in the delta.

Two issues.

The development of the delta plain towards the sea can be divided into the following three stages: 1. The delta formation period in the lower reaches of each river. The Xijiang River is outside the mouth of Sanrong Gorge, and the river branch branches. It flows into Beijiang River in the northeast and Gaoming River in the south. It was not until the Song Dynasty that the Antelope Gorge was silted up; Beijiang River

After leaving the Damiao Gorge, it radiated and divided to form the lower Beijiang Delta. Today, a main line of the Beijiang main stem is still left. After the Dongjiang River leaves the Tianluo Gorge (Boluodong), it branches into the lower Dongjiang Delta. At that time, the deltas were not connected to each other.

There are also the development of small deltas in the lower reaches of Zengjiang, Suijiang, Tanjiang, etc., which were also formed in prehistoric times.

2. Composite delta formation period In the early historical era, deltas in the lower reaches of various rivers began to unite. For example, the newly formed deltas in the lower reaches of the Xijiang and Beijiang rivers were already the product of the cooperative siltation of the Xijiang and Beijiang rivers; the deltas in the lower reaches of the Dongjiang River developed and formed in the lower reaches.

The new delta was also formed in cooperation with Zengjiang. Today's composite delta form was formed during this period.

In addition to the delta plains, there are also "point plains" deposited according to the sea surface. They are different from river flood plains. First, the river is a two-way tidal river. Second, there is no false terrace landform with high banks and low water. Third, the plains are not

It shows an inclined slope and a curved river course. It is the main tourist scenic resource of the delta and has high development value. For example, the famous "Lizhi Bay" has become one of the eight scenic spots in Yangcheng in the Ming Dynasty.

Today it is a major agricultural area, called "enclosed field area".

3. The development period of the flushed delta. After the Tang and Song Dynasties, river trunks mostly cut through the mountainous areas at the mouth of the delta front.

Outside the entrance, the river branches branch out radially, forming new deltas. For example, the Jiangmen River cuts through the Jiangmen hilly area, forming a delta in Xinhui, which is called the Xinhui flush delta; the Xijiang main road cuts through the Ganzhutan hilly area,

That is, the Zhongshan outflow delta is formed in Zhongshan City; the Beijiang trunk road forms the Panyu outwash delta in Panyu County after cutting through the Shiqiao platform and Shunde hilly land; the Xijiang trunk road cuts through the Muzhou hilly land and Dieshi hilly land.

Later, the Doumen thrust delta was formed in Doumen County.

The area known today as "Shatin District" is one of my country's rice and grain production bases.

It is also a major large-scale reclamation area in my country. There are 1.2 million acres of tidal flats outside the gate of 8 Dakou with a depth of -3 meters; 400,000 acres of shoals within 1 meter; and the coastline advances by an average of 60-150 meters per year. It varies, with annual siltation height ranging from 10 to 20 centimeters.