CONTROLLING THE YELLOW RIVER: 2000 Years of Debate on Control Strategies
Zhaoyin Wang1 and Cheng Liu2
1. Professor, Department of Hydraulic Engineering, Tsinghua University, Beijing, 100084, China. E-mail: zywang@tsinghua.edu.cn
2. Professor, International Research and Training Center on Erosion and Sedimentation, Beijing, 100048, China. E-mail: chliu@iwhr.com
Supported by UNESCO
Prepared in contribution to International Sediment Initiative (ISI) – IHP – UNESCO
ABSTRACT
Throughout the history of China, the Yellow River has been associated with frequent flood disasters and changes of the lower reach course. The river carries sediment produced by soil erosion from the Loess Plateau and Qinghai-Tibet plateau and deposit the sediment on the channel bed and in the estuary. The erosion rate accelerated in the past 2000 years due to climate changes. The sedimentation rate increased from 1-3 mm per year to 30 mm per year from 00 AD to 1855 mainly due to human activities. From 1855-1985 human activities accelerated the sedimentation at an extremely high degree and the sedimentation rate rose to 50-100 mm per year. Over time, a perched river formed that frequently breached its levees. From 602BC to 1949 the river experienced 1,593 levee bursts, flooding vast areas in 543 years and claiming millions of human lives. The river shifted its major course (600-700 km long) by avulsion 26 times with the apex around Zhengzhou resulting in devastating calamities and numerous old channels, including 8 major shifts (5 natural and 3 human-caused) with the river mouth alternating between the Bohai Sea and the Yellow Sea. Because of its wild behavior, the lower Yellow River was dubbed “the sorrow of China”. The 700 km long lower reaches have swept throughout the north China plain and left numerous old channels.
Controlling of the Yellow River has a history of more than 3,000 years. Levee construction was the major strategy of flood control. Two extremely different strategies were proposed and practiced in the past 2000 years, i.e. wide river and depositing sediment strategy and narrow river and scouring sediment strategy. Wang Jing implemented a large-scale training project in 69AD. He completed and enhanced the levees and built many diversion channels and weirs. He constructed many gates about 5 km apart on the grand levees. The river was confined by the enhanced levees tens of kilometers apart, giving enough space for sediment depostion. The riverbed silted up at a low speed of less than 1-cm per year. During great events water and sediment were diverted through the water gates into diversion basins. In the following 800 years the river was calmed and no big flood disasters occurred.
From 850AD to 1500AD the river woke again and became very active. Sedimentation on the riverbed resulted in high flood stage approaching the crest of the grand levee. The Grand Levee was breached once per 2 years during the period. Closing the breached levee was a hard job for the river training engineers and the technology of levee defence was developed. Because of the population growth, the flood diversion strategy was more difficult to implement. Pan Jixun proposed the strategy of narrowing the river and confining the flood within the stem channel in order to raise the velocity and keep high the carrying capacity of the flood, preventing sediment from depositing and even promoting bed sediment scouring. He regulated the levee system, blocked many branches of the river and made the river flow in a single channel in the lower reaches in the period 1565-1592. After Pan Jixun the sediment deposition in the lower Yellow River channel sped up to 5-10 cm per year. The river migrated from south to north and captured the Daqing River in 1855 due to the levee breach at Tongwaxiang.
Since the 1950s the Yellow River Water Conservancy Commission (YRCC) has been the leading institute for river training. Wang Huayun, the chief of YRCC, proposed and implemented his training strategies in the period. The main strategies are to reduce flood discharge with reservoirs, enhance the capacity of the river channel by enhancing and reinforcing the levees, and retending floodwater with detention basins. These strategies are referred to in short as: build a wide river and reinforce the levees, upper reaches storing, lower reaches discharging and two sides retaining. Wang’s strategy is almost the same as that proposed by Wang Jing.
This paper analyzed the levee breaches and flood disasters in the past 2000 years and the results of the two extremely different strategies. The narrow river and scouring sediment strategy has only short term effect on levee breach control and flood mitigation. The wide river and depositing sediment strategy can essentially mitigate flood disasters and reduce levee breaches for a long term period of time. The paper also discussed the new challenges and new strategies for the Yellow River training and management. Sanmenxia Project was the first large dam on the Yellow River, which was regarded as a failure in the modern river training because extremely high rate of sedimentation caused flood in the Weihe River and the benefit from power generation had to reduced to the minimum. The last chapter discussed merit of the project, its role in the river training strategy and future fate of the dam.
Key words： Yellow River, Levee breaches, Avulsion, Wide river and deposting sediment strategy, Narrow river and scouring sediment strategy, Sanmenxia Reservoir, Land creation