A wonderful phenomenon in nature: the “creator” of the “clear distinction” is actually this!

The idiom "荆魏分明" comes from "The Book of Songs·Beifeng·Gufeng", which means that the water of the Jing River is clear, while the water of the Wei River is muddy. When the water of the Jing River flows into the Wei River, the clear and muddy water do not mix. It is a metaphor for clear boundaries or clear right and wrong. Why does the situation of 荆魏分明 occur? Sediment plays a vital role in it.

In the northern suburbs of Xi'an, Shaanxi Province, two rivers meet. One is called Jing River, which has little sediment and clear water; the other is called Wei River, which has a lot of sediment and muddy water. After the two rivers meet, there is a long section where one side is clear and the other side is muddy, with a clear boundary. This is the origin of the idiom "荆魏分明". The creator of this phenomenon is an important research object in hydrology - sediment .

Silt is granular and very small. The smallest of them often floats proudly in the flowing water, muddying the river, and is called suspended sediment . There is another type that is slightly larger, but is relatively "lazy", always lying on the riverbed, and only moves forward when the water pushes it, so it is simply called bedload .

The sediment suspended in the water is called suspended load, and the sediment lying on the riverbed is called bedload.

As the flow rate slows down, the silt gradually settles on the riverbed, especially in the lower plain estuaries, forming large river beaches, creating fertile land, nourishing organisms, and promoting agriculture, making great contributions to the development of human civilization. It is also a widely used building material.

However, too much sediment is not a good thing. Common hazards include river diversion, reservoir siltation, project scrapping, blocked waterways, and ship stranding.

Facing nature, what hydrology needs to do is to find scientific countermeasures to promote benefits and eliminate harm, and turn harm into benefits. Monitoring sediment is the first step towards this goal.

Zhang Rong of the Western Han Dynasty proposed a solution to the river sediment problem

Monitoring of sediment has existed since ancient times. In 4 AD, Zhang Rong, who was famous for her water management methods, advised the court that 60% of the water in the Yellow River was sediment, and the sediment problem should be solved by using the water flow speed. This method has been confirmed by the current high flood sediment monitoring in the upper reaches of the Yellow River, as well as the effect of using reservoirs and other water conservancy projects to adjust water and sediment. This shows the wisdom of the ancients in water management.

To monitor sediment, engineers invented sediment samplers to extract river sand samples. Then, through a series of professional methods, they detect the amount of sediment, the size of the particles, and its distribution throughout the river, so as to understand the laws of river sediment.

The bigger the flood, the more sediment there is, and the more intensive the monitoring needs to be. In the turbulent rapids, hydrologists braved the storms and even risked their lives to extract sediment samples.

Hydrologists use sand meters to measure the sediment content in river water.

This operation is repeated, and often a measurement process takes several hours or even more than ten hours. In the end, such a test only leaves one point on the hydrological analysis chart. Every year, hydrology needs hundreds or even thousands of such points to analyze the amount and change pattern of river sediment.

In recent years, engineers have finally invented and developed a new instrument - a sand meter, which can measure the sediment content in water. According to different principles, there are mainly photoelectric, ultrasonic and vibration sand meters.

The size of sediment particles is analyzed by ruler measurement, screening and sedimentation methods. Because the particle size of sediment in rivers in my country varies greatly, sometimes several methods need to be used at the same time. At present, the laser particle size analyzer is widely used in my country to analyze the particle size of sediment.

my country's sediment research is world-leading. By the way, in 1957, the Yellow River's mainstream sediment transport reached 1.6 billion tons. If more than 1.4 billion people were asked to carry it today, each person would have to carry more than one ton on average. However, in the past 20 years, the ecological management of the Loess Plateau has achieved remarkable results, and the sediment entering the Yellow River has been greatly reduced.

I see

River sediment: rock and soil granular material that is transported by water flow in a river or eroded and deposited on the riverbed.

Sediment transport rate: the weight of sediment passing through a certain section of a river per unit time.

Suspended sediment: sediment that is suspended in water due to the turbulence of water flow and moves with the water flow.

Bedload: sediment that rolls, slides, jumps or moves in layers along the riverbed due to the drag of the water flow.

Reference material: "Popular Science Books on Hydrological Knowledge"