26 February 2021
Badong, China: population relocation due to landslides associated with the Three Gorges Dam
The Three Gorges Dam in China is without doubt one of the greatest feats of engineering. Lifting the level of the Yangtze River by 175 m, it created a reservoir that is 660 km long. The dam generates electricity, moderates floods and provides a navigable river for large ships, opening up central China for economic development.
Early in the project it was clear that landslides would be substantial hazard along the banks of the Three Gorges reservoir. It subsequently became clear that the magnitude of the hazard was substantially under-estimated, such that far more people would need to be relocated away from hazard zones. However, dispute the publication of case studies it has been difficult to determine the true impact of the landslides along the reservoir banks since the water level was raised over a decade ago.
A really interesting paper (Gong et al. 2021) has just been published in the journal Engineering Geology – this paper is open access – which explores this issue. It focuses on Badong, a county within the Three Gorges area, whose county seat has been relocated on three occasions due to landslides. The graphic below, from the paper, illustrates the series of events:
The original site of the county town of Bandong, Jiuxianping, was located on the northern bank of the Yangtze River. It was subject to repeated flood events, causing some relocations to occur, but in the Middle-Late Southern Song period it was moved to Xinling Town on the southern bank, probably because of a major debris flow.
However, Xinling town was close to the level of the river, and thus became unviable with the elevation of the water level associated with Three Gorges Dam. Xinling was also subject to problems with landslides. Thus, between 1982 and 2003 a plan was developed to relocate the population of Xinling to Huangtupo. The image below shows the locations of the various towns in the paper:-
Unfortunately, Huangtupo proved to be a problematic site. Shortly after construction started in 1982, evidence of slope instability instability emerged. A site investigation in 1988 identified two large ancient landslides. On 6 August 1991 large debris flows occurred in the area, triggered by an intense storm. These debris flows destroyed the southern part of Xinling, killing three people and injuring a further 171 individuals.
In 1995, two landslides further landslides occurred in Huangtupo, killing five people and causing substantial levels of economic loss. As the lake level rose further landslides were reported. In consequence, a decision was made to relocate the county town of Badong once again, this time to Xirangpo and Guandukou. Between 2007 and 2017 , over 15,000 people were relocated. Most of the buildings on the landslide complex at Huangtupo were demolished.
This paper provides a fascinating insight into both the landslides and the population relocations associated with the Three Gorges Dam programme. The underlying susceptibility of this area to landslides is well-illustrated by Gong et al. (2021). I have repeatedly noted on this blog that many landslide problems associated with hydroelectric dam projects come from a failure to identify existing ancient landslides in the landscape – a failure of the ground investigation phase of the project. This is the case here; the site of Huangtupo was underlain by a landslide complex with a volume of 69.2 million m³. It is unsurprising that this complex was reactivated when the reservoir level was raised.
Gong, W., Juang, H. and Wasowski, J. 2021. Geohazards and human settlements: Lessons learned from multiple relocation events in Badong, China – Engineering geologist’s perspective. Engineering Geology, https://doi.org/10.1016/j.enggeo.2021.106051.