Physical geography of the Pearl River basin

The Pearl River is a big river in the south of China, covering Yunnan, Guizhou, Guangxi, Guangdong, Hunan, Jiangxi and other provinces, Hong Kong and Macao and the northeast of the Socialist Republic of Vietnam, with a drainage area of 453,690 square kilometers, including 442 100 square kilometers in China.

The Pearl River Basin is bordered by Nanling in the north, South China Sea in the south, Yunnan-Guizhou Plateau in the west, hilly basin in the middle and delta alluvial plain in the southeast, with high terrain in the northwest and low terrain in the southeast. The land resources in the whole basin are * * * 663 million mu, including 72 million mu of cultivated land and 0/89 million mu of woodland. The cultivated land rate is lower than the national average, and the per capita land in the basin is only 9.3 1 mu, which is about three-fifths of the national per capita land. The Pearl River Basin is located in the subtropical zone, and the Tropic of Cancer runs through the middle of the basin, with a mild and rainy climate. The annual average temperature is between 14 ~ 22℃, and the annual average rainfall is 1200 ~ 2200mm. The rainfall distribution obviously decreases gradually from east to west, and the rainfall distribution is uneven during the year, with great regional differences and great interannual changes.

The average annual runoff of the Pearl River is 569.7 billion cubic meters, including 238 billion cubic meters in Xijiang, 654.38+0394 billion cubic meters in Beijiang, 654.38+0238 billion cubic meters in Dongjiang and 78.5 billion cubic meters in Delta. Runoff distribution is extremely uneven during the year. The flood season from April to September accounts for about 80% of the total annual runoff, and it exceeds 50% in June, July and August. The Pearl River is rich in water resources, with a per capita water resource of 4,700 cubic meters, which is equivalent to 1.7 times of the national average. However, the inter-annual changes and uneven distribution in time and space have led to frequent natural disasters such as floods, droughts and salinization in the basin.

The flood in the Pearl River basin has the characteristics of high peak, large volume and long duration. The main weather systems that cause floods in the basin are front or stationary front and southwest trough, followed by tropical depression and typhoon. Rainstorms and floods often occur in June, July and August every year.

The dry season of the Pearl River Basin is generally from June 1 1 to March of the following year, and the average dry runoff for many years is 80.3 billion cubic meters, accounting for only about 24% of the annual runoff of the whole basin. The minimum flow rate of Wuzhou Station in Xijiang River in dry season is 720 cubic meters per second, Beijiang Cornerstone 130 cubic meters per second, and Boluo Station in Dongjiang River is 3 1.4 cubic meters per second.

The Pearl River is a river with little sediment, with an average sediment concentration of 0.249 kg per cubic meter for many years and an annual average sediment concentration of 88.72 million tons. According to statistical analysis, about 20% of the sediment is deposited in the net river area of the Pearl River Delta every year, and the remaining 80% is exported to the South China Sea through eight gates.

Tides in the Pearl River Estuary belong to an irregular semidiurnal tidal cycle. The Pearl River Estuary is a weak tidal estuary with a small tidal range, with an average tidal range of 0.86 ~ 1.6m and a maximum tidal range of 2.29 ~ 3.36m ... The annual average of total high tide in eight ports is 376.2 billion cubic meters, and the annual average of low tide is 702.2 billion cubic meters, with a net decrease of 326 billion cubic meters. The Pearl River Basin is a complex basin, which consists of four water systems, namely Xijiang River, Beijiang River, Dongjiang River and the rivers in the Pearl River Delta. Xijiang River and Beijiang River meet the Pearl River Delta at Sixianjiao, Sanshui City, Guangdong Province, Dongjiang River meets the Pearl River Delta at Shilong Town, Dongguan City, Guangdong Province, and joins the South China Sea via Humen, Jiaomen, Hongqi Gate, Hengmen, Modaomen, Jiti Gate, Hutiaomen and Yamen.

The mainstream Xijiang River originates from Maxiong Mountain in Qujing City, Yunnan Province, and flows into the South China Sea at Modaomen Enterprise in Zhuhai City, Guangdong Province, with a total length of 22 14 km. Xijiang River consists of Nanpanjiang River, Hongshui River, Qianjiang River, Jiang Xun and Xijiang River, and its main tributaries are Beipanjiang River, Liujiang River, Yujiang River, Gui Jiang (Lijiang River) and Hejiang River. The river above Sixianjiao is 2075 kilometers long, with a basin area of 353 120 square kilometers, accounting for 77.8% of the Pearl River basin area.

Beijiang River originated in Damaoyuan, Xinfeng County, Jiangxi Province. The river above Sixianjiao is 468 kilometers long, with a basin area of 467 10 square kilometers, accounting for 10.3% of the Pearl River basin area. It is the second largest water system in the Pearl River Basin. The main tributaries are Wujiang, Jiang Ge, Lianjiang and Suijiang.

Dongjiang River originated in Ji Ya, Xunwu County, Jiangxi Province. The total length of the river above Shilong is 520 kilometers, and the basin area is 27,040 square kilometers, accounting for 5.96% of the Pearl River basin area. The main tributaries are Xinfeng River and Xizhijiang River.

The Pearl River Delta covers an area of 26,820 square kilometers, with dense river networks and vertical and horizontal waterways. The main rivers flowing into the Pearl River Delta are Liuxi River, Tanjiang River and Shenzhen River.