This undated photo shows a bird's-eye view of the Yellow River Delta Natural Reserve in Dongying, Shandong province. (WANG NAN / XINHUA)
Dongying, where the Yellow River flows into Bohai Bay in Shandong province, may be the fastest-growing city in the world.
Silt deposits from the river, in which 1 cubic meter of water can carry as much as 1.7 metric tons of the material, have increased the city's land area by 20 to 35 square kilometers annually.
The city's land and surrounding areas, which cover 6,000 to 7,000 sq km, were formed over the course of hundreds of millions of years from deposits carried by the Yellow River from the Loess Plateau, about 1,000 km away.
Along with the fall in water flow, the building of large dams, and the rise in population－which has caused pollution along the waterway－the Yellow River has seen a remarkable decline in its biodiversity
Yet the highly reduced levels of water and silt flowing in the river led to the sea encroaching on its estuary in the 1990s.
Zhu Shuyu, a wetland researcher at the Yellow River Delta Natural Reserve Administrative Bureau in Dongying, recalled the days when she arrived in the delta area after leaving college in 1993.
"In the mid-1990s, the river dried up for 100 days on average every year. This led to severe deterioration of the delta environment. Wetlands in the river estuary shrank by a large margin, and large numbers of birds and fish died," Zhu said.
Conditions started to change in 2002, when the Yellow River Conservancy Commission began to use the Xiaolangdi Hydro Power Project on the middle reaches of the river in Jiyuan county, Henan province, to regulate the river flow by storing floodwater to be released in drought seasons.
The project, which was completed in 2001, comprises a 12.65 billion-cubic-meter dam and a reservoir behind it.
Dykes were built in the river estuary wetland to conserve water, helping to restore surface runoff and supplementing groundwater supplies, enabling the gradual restoration of the wetland ecological system.
Since 2002, about 23,333 hectares of degraded wetland have been restored, the number of bird species living in the delta wetland has risen from 283 to 368 and the bird population has reached 3 million to 4 million.
"The Oriental white stork, a rare migratory bird species, did not breed in the delta before. Now they settle here. Since the first Oriental white stork came here in 2005, about 1,200 have been born in the delta wetland," Zhu said.
Guo Jiansan, a bird watcher from Dongying, said, "Spring and autumn are the two seasons for bird lovers in Dongying, as millions of migratory birds pass through the Yellow River Delta wetland, providing us with a golden opportunity to observe them."
Tourists from China and overseas make some 20 million trips to Dongying every year, and the wetland is a must-see spot on their itineraries. The Dongying city government estimates the wetland brings in about 17.6 billion yuan (US$2.62 billion) in tourism revenue annually.
The water in the Yellow River also makes it possible for farmers to plant crops that generate more income.
Since 2002, Yang Shijian, a farmer in Luojiawuzi village on the river estuary, has planted rice on 187 hectares of land, which he sells to dozens of cities nationwide. He has increased his annual income from about 30,000 yuan to hundreds of thousands of yuan. "The Yellow River's water is the source of wealth," Yang said.
Since 2002, the number of bird species in the delta wetland has risen from 283 to 368 and the bird population has reached 3 million to 4 million. (PENG YUAN / XINHUA)
The river rises in the heart of the Qinghai-Tibet Plateau and runs for 5,464 km through nine provinces before flowing into Bohai Bay. It is China's second-longest river after the Yangtze, and the world's sixth longest.
Nearly 6,000 years ago, the country's earliest agricultural communities and activities boomed on the plateau as a result of the area's fertile soil, abundant water supplies and humid weather.
Li Fengjiang, a geological researcher at the Chinese Academy of Sciences, told Chinese National Geography magazine, "The rich deposits of microfossils indicate the Loess Plateau used to be covered with thick plants, and later grasses, just 20,000 years ago", indicating a combination of fertile soil and a humid climate.
The other challenge is the sharp reduction in silt carried by the river. This has led to renewed fears that if the decline in silt and water flow continues, it is only a matter of time before the sea encroaches further and the delta's ecological system is degraded again
The Loess Plateau was made up of sand and soil carried by wind from deserts in Northwest China. The sand and soil were blocked by mountain ranges in the south and east of the plateau.
The soil layer on the plateau is dozens of meters deep, compared with a typical depth of 1 to 1.5 meters, providing a solid foundation for agriculture to thrive over thousands of years, Li added.
Li Qinye, a geography and resources researcher with the Chinese Academy of Sciences, said, "Although human activities on the Loess Plateau have caused serious soil erosion, ecological restoration projects and strict control of population growth can change the environment and ensure sustainable development in the region."
Yang said, "Local residents' environmental awareness should be raised and the population should be concentrated in more-habitable places to ease the burden on this vast area."
It is estimated that in the 20th century the Yellow River carried 1.6 billion tons of silt on average from the Loess Plateau each year, of which about 1 billion tons ended up in Bohai Bay. Of this, 40 percent was deposited in the river estuary, and the rest on the riverbed on its course to the sea, elevating the riverbed.
But the huge load of silt－an invaluable agricultural and environmental asset for those living on the middle reaches of the river and in Dongying－is a problem for people living in downstream areas of the river, mainly in Henan and Shandong, which are home to about 200 million citizens. They must build higher dykes in case the river overflows its banks.
Silt that piled up led to several deadly floods on the middle reaches of the Yellow River when it overflowed.
For example, flooding in 1332 and 1333 during the Yuan Dynasty (1271-1368) claimed about 7 million lives, reportedly the heaviest death toll caused by a natural disaster in human history. Flooding in 1887 during the Qing Dynasty (1644-1911) took 900,000 to 2 million lives.
Many cases of flooding triggered public anger and led to those in power being overthrown.
The Yellow River has also been used as a "weapon". In the 17th and 20th centuries, dykes were opened to flood vast areas of land in a bid to block advancing rebel farmers and Japanese invaders.
The elevated riverbed means it is almost impossible for subsiding floodwater to find its way back to the river. Instead, it merely flows to lower-lying land and nearby rivers. During this process, the Yellow River has changed its course.
Statistics from the Yellow River Conservancy Commission, founded by the Communist Party of China in 1946 to control the river in Zhengzhou, Henan, show it flooded 1,593 times from 595 BC to 1946, and had shifted its course 26 times.
The estuary area has fluctuated from the Haihe River in the north, which flows into Bohai Bay, to the Huaihe River in the south, which flows into the Yellow Sea. The two river mouths are nearly 900 km apart.
Frequent flooding and related natural disasters have prompted efforts to minimize the financial implications, with large areas of land earmarked as zones to control flooding.
Hukou Waterfalls, the largest on the Yellow River, is located where Shanxi and Shaanxi provinces meet. (LYU GUIMING / FOR CHINA DAILY)
Since the 1950s, dozens of dams and reservoirs have been built along the river in an attempt to control it, resulting in no major instances of flooding or changes to its course.
The Xiaolangdi Hydro Power Project, the second-largest water conservation program in China after the Three Gorges Dam on the Yangtze River, ensures sustainable water supplies to the middle and lower reaches of the Yellow River, even in times of drought.
Meanwhile, the population living along the river has been rising fast, with the Yellow River Valley now home to some 150 million people. It also sustains about 15 percent of the country's crop output and 6 percent of its industrial production.
In the 1950s, about 50 billion cu m of water flowed from the Yellow River into the sea. Now, the figure is only about 20 percent of that at most.
Along with the fall in water flow, the building of large dams, and the rise in population－which has caused pollution along the waterway－the river has seen a remarkable decline in its biodiversity.
Like the Yangtze, it is believed that the fish population has almost been depleted in most parts of the middle and lower reaches of the Yellow River
Like the Yangtze, it is believed that the fish population has almost been depleted in most parts of the middle and lower reaches of the Yellow River. Many experts claim that these sections lost the ability to restore themselves long ago.
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The other challenge is the sharp reduction in silt carried by the river. Over the past 15 years, it has carried from the Loess Plateau only 270 million tons on average each year, a sharp contrast with the 1.6 billion tons annually in the 20th century. But the perennially dirty waters of the river on its central and lower reaches have become much cleaner.
A series of measures have reduced the amount of silt the river carries, easing the pressure to build dykes in Henan and Shandong, but causing new problems in Dongying.
The measures include a campaign on the Loess Plateau to return grain plots to forestry use. This has increased the proportion of forest coverage in the center of the plateau from 10 percent to nearly 50 percent over the past 19 years.
Desertification control measures have been taken in the Inner Mongolia and Ningxia Hui autonomous regions and about 20 dams have been built on the middle reaches of the river.
In 2016, the amount of silt the river carried to the sea in Dongying was only 10 million tons, and the water flow, although uninterrupted, has remained only one-third of its runoff on average. This has led to renewed fears that if the decline in silt and water flow continues, it is only a matter of time before the sea encroaches further and the delta's ecological system is degraded again.
Wang Pengfei, an official with the Dongying land and resources bureau, said: "Many people are urging the authorities to increase Dongying's water quota from the Yellow River to protect the delta wetland. But this is easier said than done."
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