On October 28, 1997, the Yellow river was diverted into tunnels on the north bank at Xiaolangdi, about 40 kilometres north of Luoyang in Henan province, and the river bed was closed off, and the main dam was built across it. The diversion was a step in a large project that was intended to control floods and to trap silt on the lower reaches of the river. The work was one of the biggest civil engineering projects in the country.
The purpose was to deal with two old problems. The Yellow river carries a very heavy load of silt, and it deposits it on the bed of its lower course, which is in places higher than the land around it, and the river has broken its banks and changed course many times with great loss of life, and the long dry periods in the north also made the supply of water a concern. The river was feared. The reservoir behind the dam is designed to hold back floods and to let sediment settle, and the scheme includes a power station with a large capacity, and tunnels and spillways to pass the flood water.
The project had been discussed for decades and was approved in the early 1990s, and it was carried out with foreign contractors and with loans from the World Bank, and the main works were finished in 2001. The work took years. It displaced a large number of people, who were moved to new settlements, and the reservoir covers former farmland and a number of villages. The environmental and social effects have been studied closely since.
The reservoir has been used to release water and sediment in planned pulses that flush the lower channel and slow the rise of its bed, and the scheme has reduced the risk of a major flood, and it also supplies water and electricity. The risk fell. The river remains difficult to manage, and experts disagree about how long the reservoir will be able to hold silt, and the project is one of the cases most studied in the management of heavily silted rivers.