A little geological context:
Farther west from where these maps show, the Huang He/Yellow River flows through a region of north central China called the Loess Plateau. It is called this because it is a huge accumulation of fine, dusty, silty soil that erodes very easily.
So a lot of loess ends up washing along with the river, turning the water a muddy yellow brown that gives the river its name. So far so good, and as long as the river keeps rushing along down the mountains a bit of extra loess isn't a problem, right?
Then the land runs out of mountains. Things flatten out as you head east and approach the sea. The Yellow River slows down as it hits the plains, and it can't keep as much mud in suspension, and all that fine, dusty, silty mud settles out.
On the one hand, this is great news! Loess deposits make for some very fertile soil, and this area of China becomes a breadbasket because stuff grows so well. On the other hand, a lot of those deposits are building up on the riverbed and leaving less and less room for, y'know, the river itself.
So the river periodically overflows its banks and finds/scours a new channel to follow. It's not particularly bothered by pesky little things like the thousands or millions of people who might have been living there before. A river's primary concern is following gravity; mass death just kinda happens sometimes.
And this is a big enough thing that it builds into local mythology. The first emperors are credited with having started massive civil engineering projects to build levees and keep the flow of the river under control. ... the only problem is, there's still tons and tons of loess flowing in every year, and it's still piling up in the riverbed. All the levees did was buy them time.
So they build the levees higher. And higher. Until the bottom of the river was technically above the surrounding land. And if the levees ever broke ... well, look at 1289 up there, when the Yellow River became a tributary to the Chang Jiang/Yangtze for 35 years. And there was still so much loess in the river that it filled in an entire bay of the Bo Hai sea over the centuries!
Nowadays, there are massive projects on the river specifically to control the amount of loess in the water and dredge out the sediment deposits before they build up and send the river skipping merrily across an unsuspecting county. Hopefully this works a bit better.
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