Posted on October 6th, 2015

Our Changing Landscape – Three Gorges Dam, China

In this monthly feature, we span the globe to examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 5 billion square kilometers of data. This month, we look at Three Gorges Dam in China to see how the massive project has changed since its completion.

The RapidEye Constellation

RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers daily revisits to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a starting cost of $1.28 per square kilometer for all five spectral bands – academics do receive discounts. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape.

Three Gorges Dam, China

ThreeGorges_Anime_REClick on the image above to see an animation of 5-meter natural color RapidEye imagery collected over Three Gorges Dam in China on November 22, 2009, December 2, 2010, June 12, 2012 and October 2, 2014. In this animation, you will see that the water level behind Three Gorges Dam changes significantly over time. Which makes sense as rain patterns vary by year and season, and these images come from a time period covering June to December and then 2009 to 2014. What we find particularly intriguing about these images is in the 2012 and 2014 data. If you look at the northeastern edge of the dam in the 2012 image, you will see a new linear feature that looks to be a boat channel. But then in the 2014 image where the water levels are very high, it appears that sediment is building up quickly where the boat channel lane was built. We are not engineers by any stretch of the imagination but it is interesting to see what appears to be sediment buildup behind the dam. And then when you consider this in light of the predictions that Three Gorges Dam would not operate as long as predicted given how muddy the Yangtze River is, this is truly intriguing to us! (Images Courtesy: RapidEye)

Sometimes (or perhaps often) the topics we cover in our Geospatial Times articles are self-serving, and well, this is one of them. Since I heard about the Three Gorges Dam many moons ago, it intrigued me; I mean come on, this dam is huge and I have seen the Hoover Dam which is quite the site. Consider that the Three Gorges Dam is some 7,661 feet long and 594 feet high (from its rock base) versus the Hoover Damn which is only 1,244 feet long and then 726 feet high (okay it wins there!). A quick calculation confirms that Three Gorges Dam covers more than 5 times the river opening (i.e. its surface area so to speak) than does Hoover Dam.

And since the intent of this article is to feature the visual information we can find in 5-meter RapidEye imagery, I will not spend much time on the history, economic logic and controversy of Three Gorges Dam as it has been covered nicely many other places (for example on Wikipedia). If our readers have never heard of the massive dam, here are a few sentences to get you situated. Three Gorges Dam is the world’s largest operational dam as well as the largest power station regardless of energy source. It is located in east-central China, damming the outflow of the mighty Yangtze, Asia’s longest river and the third longest in the world. As of 2012, the project costs were estimated at $28 billion which could be recuperated after 10 to 15 years of full power-generating operations. And while the Three Gorges generates about 2% of China’s total electricity demand, the dam is repeatedly cited for the massive (and mostly negative) environmental and societal impacts it has caused – take for example the 1 million plus Chinese citizens who were displaced when it was built and flooded the areas around the Yangtze.

It is not the intent of this Our Changing Landscape to take a stand on the Three Gorges Dam either in favor or against the massive structure. Rather, it is time to let the images speak for themselves – enjoy!

If you would like to find out more about using RapidEye for your academic studies, engineering projects or any landscape analysis, let us know at sales@apollomapping.com or (303) 993-3863.

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