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1 The Evolution of theYellow River Control System in Late Imperial China, 1495–1835 The Yellow River is a restless, unpredictable, and dangerous stream. It has changed course many times since records were first kept, and its countless floods have wrought terrible destruction on the North China region. Yet for all its destructive power, it is not a large river. Its average discharge of 1,365 cubic meters per second (m3/s) is a mere dribble compared to that of a behemoth like the Amazon (180,000 m3/s) or even that of the Mississippi (17,545 m3/s).1 The Yellow River’s history of destruction arises from two unfortunate characteristics: most famously, the river carries a huge quantity of silt; but equally important is the radical variation in the river’s flow, from a trickle in the dry periods to a raging torrent during flood season. The trouble starts when the river turns south at the top of the “great bend” and begins to drop, falling almost nine hundred meters as it travels across the loess plateau between Shaanxi and Shanxi Provinces. The plateau is an arid, almost lunar landscape where deposits of powdery loess soil hundreds of meters deep have been carved into stark, treeless arroyos that branch out from the river’s main channel in an endless fan of tributaries. Every heavy rain that falls on the deforested, overgrazed hills sends streams of mud cascading into the river. Runoff from the loess plateau also feeds major tributaries like the Wei and Wuding Rivers, which in turn contribute to the Yellow River’s silt burden. By the time the river turns east onto the North China Plain, it carries an unrivaled thirty-four kilograms of silt per cubic meter of coffee-colored water. It is estimated 11 that the Yellow River produces 920 million cubic meters of sediment per year; only the Amazon at 1 billion cubic meters per year and the Mississippi at 980 million produce more.2 When that muddy torrent emerges from the mountains, it slows to a crawl. For the next eight hundred kilometers, from a point just west of modern Zhengzhou to its outlet (most commonly in the Bohai Gulf or the Yellow Sea), the turbid river drops only ninety-five meters. The velocity of a stream determines how much silt it can carry; as the river slows, the loess soil settles out. Before the river reaches the sea, it deposits an estimated 40 percent to 50 percent of its silt burden in its channel. As a result the bed in the downstream provinces rises steadily. Seasonal high water levels deposit sediment along the banks of the river, allowing the bed inside the banks to rise above the land outside. Eventually the river breaks through its banks to seek a lower course. Over the centuries, flooding and the resulting sedimentation have created a cone-shaped elevation along which the river flows until it encounters the Shandong massif, at which point it is deflected north or south.3 The construction of dikes to prevent a change of course exacerbated the rise of the river’s bed so that it stood well above the surrounding plain along much of its lower course. As it slows, the river forms great loops known as meanders (zuowan) within its dikes. Those bends threaten the dikes in several ways. Their primary danger lies in the fact that the current on the outside of a meander moves much more quickly than the current on the inside, carving at the soft soil of the riverbank with great erosive power. Keeping those erosive forces away from the dikes was one of the fundamental goals of river control. Huge defensive structures several kilometers long were built to deflect the current back out toward the center of the riverbed. As the river rose during flood season, the huge loops could carve their way up and down the channel at alarming speed. In a span of hours, the river could move to threaten a section of dike that had been hundreds of meters from the water. In extreme cases the current might swerve ninety degrees and strike the dike almost perpendicular to it. Immediate action was required to prevent the current from tearing through the dikes. The erratic rainfall patterns typical of the North China climate also complicated river control. For much of the year, the Yellow River is small stream; but when the rains come, the river quickly can swell to...

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