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Posted on November 3rd, 2020

Our Changing Landscape – Yangtze Flooding and the Three Gorges Dam

In this monthly feature, we span the globe to examine Our Changing Landscape with a time series of medium-resolution PlanetScope satellite imagery. The PlanetScope constellation dates back to 2016 and collects hundreds of millions of square kilometers of 4 and 5-band 3-meter imagery daily! Last month we stayed local with a look at the Pine Gulch Fire, and for the October Our Changing Landscape we travel to the other side of the world, with a look at China’s Three Gorges Dam as it’s put under pressure from flooding along the Yangtze river.

Click on the image above to see an animation of 3-meter natural color PlanetScope imagery collected over Three Gorges Dam in Yichang, Hubei, China on August 14, August 26, September 4, September 5 and September 24, 2020. In this animation you can see two major changes. First, in the August images the middle sluice gates were wide open but by the first September image it is down to just a single gate; and then in the final dates, the sluice gates are closed. Second, you can see changes in the shoreline as water levels in Three Gorges Dam vary across the dates. It appears that water levels are the highest in the August 24th image but that is not consistent across the entire shoreline. Similar changes in water levels can be detected in the Yangtze river to the east of Three Gorges Dam. (Images Courtesy: © Planet 2020)

The PlanetScope Microsat Constellation

PlanetScope is a constellation of more than 150 microsats referred to individually as Doves. Each Dove is able to collect up to 20,000 square kilometers (sq km) per day of 3-meter (m) 4-band multispectral (i.e. blue, green, red and near-infrared [NIR]) imagery; and newly launched SuperDoves collect 5-band multispectral adding in valuable red-edge spectral data. Across the constellation, PlanetScope is archiving more than 200 million sq km of medium-resolution imagery a day, making it the go to source for daily imagery over most locations. This massive archive dates back to 2016, offering the most complete and continuous record of spatial data on the planet since the start of the constellation’s ongoing launch schedule. Collecting 3-meter multispectral imagery is the equivalent of ‘high-resolution’ multispectral data imaged by a 75-centimer (cm) satellite (as this satellite would feature 75-cm panchromatic and 3-m multispectral), making PlanetScope an extremely competitively priced option at just $1.80 per sq km. With well registered images and nearly daily collections of most locations, PlanetScope is the ideal imagery source for this current-events focused series, Our Changing Landscape.

Yangtze River Flooding Puts Pressure on Three Gorges Dam

With seasonal rainfall totals more than double the regional average, the Yangtze river has seen significant flooding in 2020 which matches the trend across China as the nation has been ravaged by more than $29 billion in flooding damage. As of August 20th, the Yangtze was pouring more than 75,000 cubic meters per second of water into the Three Gorges Dam reservoir, pushing water levels to 165.6 meters which is less than ten meters shy of the maximum designed depth of 175 meters. This increase in reservoir water levels prompted Japanese media to publish a commentary voicing serious concern for a pending human and natural disaster.

While we know that Three Gorges Dam was never breached in the end, summer 2020 shows that the megastructure is vulnerable, particular as global Climate Change puts additional pressure on it. Apparently 2020 was the first time since the dam started producing power in 2013 that local operators were forced to open its sluice gates to protect Three Gorges from over-breaching, as on August 20th 11 of the 22 gates were opened. Given the near-daily collection rate of the 3-meter PlanetScope constellation, it is well suited to track temporal changes in reservoir water levels, so now we turn to the archive to see how the lake behind Three Gorges Dam changed from late August to September.

If you would like to find out more about using 3-meter PlanetScope imagery 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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