Filling the reservoir reactivated hundreds of ancient landslides. Now 5,000+ sensors track millimeter movements to prevent disaster from slopes saturated by rising water.
Source file: Le Grand Portage Derivative work: Rehman, CC BY 2.0, via Wikimedia Commons
The weight of water
The Three Gorges Dam created a reservoir that stretches approximately 660 kilometers upstream. This immense body of water, with a total storage capacity of 39.3 billion cubic meters, exerts enormous pressure on the surrounding landscape. The geology of the Three Gorges region is complex, featuring layers of soft rock like mudstone and sandstone that are naturally susceptible to landslides. Before the dam, these slopes were relatively stable. The impoundment of the reservoir, which raised the water level by over 100 meters to a maximum of 175 meters, dramatically altered the hydrogeological environment.
The reservoir's water level fluctuates annually in a controlled cycle: it is lowered to 145 meters during the summer wet season to accommodate floodwaters and raised back to 175 meters in the winter to maximize power generation. This repeated saturation and drawdown weakens the rock and soil. The water seeps into cracks and fissures, increasing pore water pressure and reducing the frictional forces that hold the slopes together. This process has reactivated hundreds of ancient, dormant landslides and created thousands of new danger zones. Over 5,000 landslide-prone sites are now officially monitored along the reservoir's banks.
A network of digital sentinels
To manage this immense geological challenge, Chinese authorities have deployed one of the world's most extensive landslide monitoring systems. This network consists of more than 10,000 monitoring devices of over 60 different types. The system integrates multiple technologies to provide a real-time picture of slope stability.
High-precision Global Navigation Satellite System (GNSS) receivers, including GPS, are important to the network. These instruments are installed on active landslides and can detect surface movements with millimeter-level accuracy. They provide continuous data on the speed and direction of any displacement. For a broader view, satellite-based Interferometric Synthetic Aperture Radar (InSAR) scans vast sections of the reservoir, mapping ground deformation over large areas and identifying slow-moving slopes that might otherwise go unnoticed.
On the ground, a dense array of sensors provides detailed information. Inclinometers are inserted into boreholes to measure subsurface displacement and locate the precise depth of a slide's rupture surface. Piezometers monitor the pore water pressure within the soil, an indicator of instability. Crackmeters, or extensometers, are placed across fissures to measure any widening. This data is integrated with rainfall gauges and reservoir level monitors to understand how external triggers affect slope movement. The Shuping landslide is an example landslide, a reactivated ancient slide with a volume of about 20 million cubic meters, which is heavily instrumented with GPS, extensometers, and inclinometers to track its response to water level changes.
💡Fun Facts
The annual 30-meter fluctuation in the reservoir's water level is the primary trigger for landslide activity.
The Qianjiangping landslide in 2003, triggered by the initial reservoir filling, created a displacement wave up to 30 meters high.
The monitoring system can distinguish between different landslide triggers, finding that rapid water level drawdown is a more significant factor than heavy rainfall for some major slides.
In some areas, residents can use a specially developed app to view monitoring data and upload photos of ground cracks, contributing to the early warning system.
The Three Gorges Dam Tourist Area is generally open from 8:00 AM to 5:30 PM, though hours for specific attractions may vary.
Admission
While entry to the main tourist area is often free, there is a mandatory fee for the shuttle bus service, around 35 CNY. Some viewing platforms or boat tours may have separate charges.
Accessibility
The main tourist viewing areas, like Tanziling Platform and Platform 185, are well-developed with paved paths and accessible by shuttle bus. The wider reservoir region is mountainous.
