Tiger Leaping Gorge: Another Megadam?

Rob's post below looks at the area around the megadam that everyone seems to know about - the Three Gorges Dam. Construction there started in 1994 and will only be completed in 2009, with the final rise in water level to 175m above sea level. That's a total rise of almost 80 m in sections close to the dam. That one's a done deal, with most of the construction and relocation already complete. But what the world doesn't really know about are the plans to dam the Yangtze 1500 km further upstream, in the famous Tiger Leaping Gorge of Yunnan Province. This dam would be purely for energy production, as the site is upstream of the traditional navigable Yangtze.

It's really hard to get accurate information about these dam plans. We heard several different versions from people we met, ranging from a huge single dam to a series of 8 smaller dams through the 25 km long gorge. Note that the Times Online has an article suggesting the single dam approach would yield a dam 278 m high and a reservoir almost 200 km long. An Asia Times article written also written in 2006 suggests the 8 dam plan is in the works.

Hiking through the gorge with the class gave me the opportunity to look at the area and roughly estimate it's suitability for such a dam and reservoir. As a geology professor and wannabe geotechnical engineer, it's the stuff I love to do.

First off, the rock is fairly fractured schist in the middle gorge, and fractured marble at the gorge exit where the dam would be. Not the most stable rock to be building on. I managed to find a tunnel near Walnut Grove that researchers had obviously excavated in order to look at fracturing in the marble. There are a lot of other obvious signs that geotechnical testing is underway. As I see it, one of the biggest challenges for the dam builders would be the issue of landslides. Landslide debris is found throughout the gorge, and the only road through the gorge is currently blocked by three large slides. The entire village of Walnut Grove is situated on an old landslide perhaps 2 km wide. Saturating the banks of the gorge when the water level is raised further weakens the strength of the rock, so if this many landslides are happening now, it doesn't bode well for the post-dam gorge.

So why should we care about landslides in the area, especially if they plan to move most of the people out of there? Check out the Vajont disaster that killed 1,450 people in Italy when a landslide triggered a huge wave that overtopped the dam and inundated the town below. The largest waves in the world have all been triggered by landslides into open water. If they build this dam, I wouldn't think it safe to keep any people in the valley, even if your house and land are above the new water level.

Oh yeah, the epicenter of the 1996 magnitude 7.2 Lijiang earthquake was actually in Tiger Leaping Gorge. Not good.