Earthshots: Satellite Images of Environmental Change

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» Toshka Project, Egypt
 

In southern Egypt, the sandy desert turned, temporarily at least, into a lakes region. Beginning in 1998, lakes quickly appeared and almost as quickly disappeared from Egypt’s Sahara Desert. Then, in late 2019, they appeared again. Landsat and Sentinel-2 satellites captured these remarkable changes.

These images also show the progress of the Toshka Project. Originally intended to relocate millions of Egyptians from overcrowded cities into a “New Nile Valley,” the project includes plans for hundreds of thousands of hectares of irrigated farmland. Like the lakes that formed in this region, this irrigation project relies upon water from the Nile River. The Toshka Project remains incomplete and the ambitious plan’s future is in question.

Map of the featured area.

The Aswan High Dam on the Nile River was completed in 1970 for flood protection and to store water during dry years. The dam formed Lake Nasser, the third largest reservoir in the world by volume. A small portion of this lake is visible in the lower right corner of the images.

In 1978, a spillway and channel were built as a precaution against any unexpected increase in Lake Nasser’s water level. The channel can divert water from the reservoir to the Toshka basin, which is located outside the Nile basin. This design reduces pressure on the dam and protects downstream areas from massive flooding.

In 1998, excess rainfall in the Ethiopian highlands tested the flood control plan. The huge reservoir reached its maximum stage of 183 meters above sea level in September. The overflow water streamed through the spillway and into the Toshka basin forming the Toshka lakes. Around 32 to 98 million cubic meters of water per day poured into the basin during September and October.

The lakes reached their maximum collective size in August 2001. Their area remained fairly stable through August 2003. The water supply from Lake Nasser continuously replaced water lost through evaporation. As the level of Lake Nasser subsided, the water supply from the reservoir stopped and the lakes started diminishing.

The only two places for water in this arid region to go are into the air or into the ground. The underlying limestone prevents much ground infiltration. In the Toshka region, annual precipitation averages a meager 1.5 millimeters, and the potential evaporation rate is 14–15 millimeters per day. With no natural outlet and reduced water input to these lakes from Lake Nasser, the water evaporated quickly.

These close-ups of one of the larger lakes show how the formation and reduction of the lakes affected sand dunes.

  • Sand dunes became inundated as the lakes formed. In the 2001 image, many larger dunes were small islands in the lake.
  • Bright sand dunes re-emerged as the lake level dropped. In the 2013 and 2017 images, a few dunes are still islands.
  • The darker ground in the later images indicates former water levels—the darker tone means moistened ground.

As part of the Toshka Project, a pumping station sends water from Lake Nasser to irrigated fields in the Toshka basin. The Mubarak Pumping Station has a discharge capacity of 1.2 million cubic meters per hour through the Sheikh Zayed Canal.

The pump house is like an island. Its 24 vertical pumps are arranged in two parallel lines. The intake channel is 50 meters deep, the deepest inland channel ever built. This innovative engineering marvel is even earthquake-proof.

About 138 kilometers of canals carry the Nile water from the pumping station in Lake Nasser to irrigated fields west of the reservoir. By the 2013 image, the Sheikh Zayed Canal makes a clearly visible line to the northwest from the bay where the pumping station sits.

The Landsat images show the appearance of center-pivot irrigation fields near one of the diminishing lakes. As of 2012, however, only about 21,000 hectares of farmland, less than 10% of what was planned, had been cultivated in the region.

The economic viability of this huge project has been unclear. It’s impossible to say exactly how much the Toshka Project has cost so far—estimates of the project’s final cost range up to $70 billion USD.

If more water were to be pumped from Lake Nasser to irrigate hundereds of thousands of hectares of farmland outside the Nile basin, the lake would likely never again spill into the Toshka lakes. However, with much less irrigated farmland than originally planned, excess water from the reservoir could indeed flow again into the Toshka lakes. And it did in late 2019. The animation below uses images from Landsat 8 and Sentinel-2 to show the eastern lake filling to capacity--and more--starting in early October.

Will people find enough incentive to move to the area and develop it into a “New Nile Valley”? Landsat will continue to track the status of the Toshka region and its agricultural development.

Toshka Lakes 2019 animation

References

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