Yellow River Changing Course
By Vivian Forbes 12 November, 2015
Prof. Forbes provides a detailed overview of the Yellow River & how it has changed course over the centuries
The distinctive shape of the Huang He or Yellow River is a dominant geographical feature on any small-scale topographical map of China (see below). However, the shape and alignment of the mouth of the river has changed over centuries.
The river is revered in the country – Mother River – and indeed holds a fascination for many, especially I, who was fortunate to visit just one section of the river so as to gain a first-hand appreciation of the state of the river in Zhengzhou in late-April 2014.
|The Huang He is the second longest river in China. It meanders over a course of about 5,500 km and drains an area of about 900,000 sqkm. It flows through seven Provinces and two Autonomous Regions of China. As one of the most heavily silt-laden rivers in the world, the river derives its name, Yellow River, from the muddy-colour of its water, which is a constant ochre-yellow tint. Sediment carried by the river is deposited in such large amounts on the river bed so that it raises the bed and creates a phenomenon referred to as the ‘hanging river’. In many places, the bed of the lower reaches of the Huang He is several meters higher than the surrounding land.|
The river’s alignment may be considered in three stages: the Tibetan Plateau, the Ordos Loop (‘U-shape’ of the river) and then along the North China Coastal Plain.
The source and upper reaches
The upper reaches of the Yellow River constitute a segment starting from its source (located at Latitude 34° 29’ 31.1”N and Longitude 96° 20’ 24.6” E; at an elevation of about 4,500 m) in the Bayan Har Mountains, Qinghai Province to a point at Hekou just before the river bends sharply to the south. This sector has a total length of 3,470 km and basin area of 386,000 sqkm, or nearly 50 per cent of the total basin area. Along this length, the elevation of the Yellow River drops about 3,500 meters, with an average gradient of 0.10 per cent.
This section has a length of 3,470 km & accounts for nearly 50% of the total basin area
The valley section stretches from Longyang Gorge in Qinhai to Qintong Gorge in Gansu. Steep cliffs are a feature along this section of the river which has a narrow bed. There are 20 gorges along this stretch of river. Thereafter, it flows through the alluvial regions of Yinchuan and Hetao Plains comprising deserts and low grasslands.
The middle section
The section of the Huang He between Hekou, Inner Mongolia and Zhengzhou, Henan Province constitutes the middle reaches of the river which is about 1,200 km in length, with a basin area of 344,000 sqkm, or about 45 per cent of the total, with a total elevation drop of 890 m, and an average gradient of 0.07 per cent. Between the two above-named cities, the river meanders through a series of valleys collectively termed the Jinshan Valley. Numerous hydroelectric generating plants are located along this stretch of river to take advantage of the swift-flowing waters and the narrow gorges.
This section has a length of 1,200 km & accounts for ~45% of the total basin area
There are 30 large tributaries along the middle reaches, and the water flow is increased by as much as 44 per cent at this stage of the river. The middle reaches contribute nearly 92 per cent of the river’s siltation. The deposition is brought about by the river’s alignment through the Loess Plateau and the wind-blown loess soil driven over the river. An estimated four billion tons of loess soil was deposited into the river in 1933 according to studies undertaken. The highest silt concentration level was recorded in 1977.
The lower reaches and delta
In the context of this essay, the lower reaches of the Huang He extends from Zhengzhou to the mouth of the river a distance of about 790 km. From here the alignment of the river is confined to a series of levees as it flows across the north China coastal plain in a north-easterly direction to the coast of the Bohai Gulf (which is a part of the Yellow Sea just north of the Shandong Peninsula).
This section has a length of 790 km and >5% of the total basin area
The area of the delta’s basin is about 23,000 sqkm equating to less than five per cent of the total area. The overall drop in elevation of the lower reaches of the river equates to about 90m with an average gradient of 0.12 per cent.
Changing alignment of the mouth of the Huang He
Over centuries the alignment of the mouth of the river has altered. The changing coastline in the vicinity of the delta is also depicted below.
Between the years of 1324 to 1853, it flowed south of Shandong Peninsula and entered into the Yellow Sea. The estuary spans an area between the Gulf of Laizhou and Gulf of Bohai. It has flowed to the north of Shandong Peninsula since 1855 following the breach of the embankment at Tongwaxiang, some 580km from the then river’s mouth.
The estuary covers an area of about 6,000 sqkm if the apex of the delta is located at Ninghai. It starts at the mouth of the Taoer River in the north and ends at the mouth of the Zhimaigou River in the south. The meandering nature of the mouth of the Huang He has been contained within these confines.
“There have been nine diversions of the river alignment within the estuary since 1855…
The range of diversion designs and meanders are to protect agriculture and industry…”
There have been nine diversions of the river alignment within the estuary since 1855; six of these diversions occurred between 1889 and 1953 when the apex was at Ninghai. Due to the volume of sedimentation from upstream, the Huang He estuary has been maintained at a state of deposition, extension, meandering and diversion. The range of diversion designs and meanders are to protect agriculture and industry in the estuary region and hence, has been restricted to a surface area of about 2,400 sqkm. The apex of the diversion path was moved to Yuwa in 1953 and there were three subsequent diversions.
Human-induced and natural causes of the changing alignment
Humans interact greatly with the Huang He. The river flows through 66 prefectural-level cities (autonomous prefectuals, leagues) and 340 counties (county-level cities, autonomous banners). Out of the 340 counties (county-level cities, autonomous banners), 267 are situated in the basin, while parts of 73 others are also in this area. Estimated total of population in 2006 within the basin was in excess 113 million; the rate of urbanisation is nearly 40 per cent and a population density of 143 head per sqkm. The Provincial Governments tasked with managing sections of the river include Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong.
It was pleasing to observe that Henan Province has produced an atlas that includes depicting flood-prone regions within the province and land utilisation along the river’s banks.
Humans interact greatly with the Huang He.
The river flows through 66 prefectural-level cities & 340 counties.
The construction of levees & excessive deposits of sediment have raised the river bed several metres
Given this, it is not surprising that over the centuries, construction of levees and excessive deposits of sediment from the upper reaches have raised the bed of the river several metres above the surrounding ground, for example, at Keifeng, Henan Province is about 10m above the ground level. The dynamics of the processes of siltation along the lower reaches of the Huang He and its delta is vividly illustrated in the images below in a temporal scale of the changing nature of the coast line at in the vicinity of the mouth of this mighty river.
“Seeing landscape changes makes one appreciate the fact nature cannot be commanded nor tampered with”
Nature has also changed the alignment with varied weather patterns such as droughts and floods, as well as changing silt deposits. These of course can be exacerbated by human activities.
Seeing landscape changes makes one appreciate the fact nature cannot be commanded nor tampered with.
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