We contest the views of Peiyue Li and colleagues on the geological implications of land creation projects in China, particularly for Yan'an city (see Nature 510, 29–31; 2014).
The Yan'an project has created flat ground by levelling hills and filling valleys, and was carefully planned by the local government after thorough feasibility testing by geoengineers, hydrologists, water conservationists and ecologists. The site was consequently able to withstand severe erosion caused by a once-in-a-century flood in July 2013.
Any threat of collapse of soft-soil deposits has been eliminated by repeatedly compacting the relocated soil in layers. This reinforcement strategy has increased soil-particle density from 1.9 to 2.1 grams per cubic centimetre (see go.nature.com/mqg194; in Chinese).
Guided by strict planning and controls, construction work will initially occur in the excavation area, and will not extend to filled regions until the ground stabilizes through natural sedimentation. The soil interfaces between the excavated and filled areas, slope compaction, and drainage of ground and surface water are also being rigorously monitored.
The newly created land will be used for administrative, residential and commercial purposes, so there will be no risk of industrial pollution. Almost half of the project area will be covered in vegetation.
Yan'an's experience of land creation could be useful for extending other mountain cities in China and abroad.