Earthshots: Satellite Images of Environmental Change

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South Africa needed water. Lesotho needed electricity. One huge project aims to solve both problems.

Lesotho is a small mountainous country completely surrounded by South Africa. A little smaller than the U.S. state of Maryland, Lesotho’s most important natural resource is clean water, dubbed “white gold.” Lesotho’s highlands receive about 1,200 millimeters of rainfall annually and are the main headwaters for the Orange (Senqu) River system. Most of that water leaves Lesotho, flowing east to west across South Africa, where the river empties into the Atlantic Ocean.

Measured by per capita gross domestic product (GDP), Lesotho is a relatively poor country, falling in the bottom 20 percent of countries. South Africa is one of the wealthier countries in Africa but has been experiencing water shortages. Its industrial heartland includes the large city of Johannesburg, over 300 kilometers to the north and outside of the Landsat scenes displayed here. Recurring drought and increasing demand for water have put additional pressure on water resources there.

Two dams have been completed on tributaries of the Orange (Senqu) River as part of the Lesotho Highlands Water Project (LHWP), which harnesses Lesotho’s water and exports it to South Africa. Before this project, Lesotho was dependent upon South Africa for electricity. Lesotho can now generate electricity from the dams. Additionally, hundreds of kilometers of roads were built or upgraded in Lesotho’s mountainous landscape, cutting down on travel time, in some cases by days.

Not all of the reviews of this project have been positive. Some studies have reported there may not have been enough foresight of the stress on water resources that drought and climate change could be causing. Furthermore, reduced river flows could affect communities that rely on the river for livelihoods, and some say this impact was not well understood before the project began. Besides these possible environmental consequences, many communities claim that they did not receive promised compensation for relocation.

Map of the featured area.

The first part of the LHWP was the Katse Dam. Construction started on the Katse Dam in 1991 on the Malibamats’o River, a tributary of the Orange (Senqu) River. The dam was completed in 1997 and is 710 meters long and 185 meters high.

The deep lake formed by the dam can hold 2 billion cubic meters of water, but the winding and narrow reservoir has a surface area of only 35.8 square kilometers. This small surface area minimizes evaporation loss. The 1995 image, before the dam was completed, hints at the depth of the valleys that were later filled.

This reservoir is the key to the electricity needs of Lesotho and the water needs of South Africa. A 45-kilometer long tunnel brings water from the Katse reservoir to the Muela hydropower station, which can generate 72 megawatts of electricity. Three turbines each generate 24 megawatts. An intake tower in the reservoir transfers water 82 kilometers from Lesotho to South Africa.

Unlike the Katse Dam, the Mohale Dam does not generate power. Instead, it was built as a backup reserve to the Katse Dam and reservoir. The dam was built on the Senqunyane River, another tributary of the Senqu/Orange River. The Mohale reservoir began filling by the time of the 2003 image.

The Mohale Dam is 145 meters high and 620 meters long. It is the highest concrete-faced rock-filled dam in Africa. A large basalt hill inside the basin had to be crushed to build the rock wall. The dam then formed the 21.2-square-kilometer Mohale reservoir. A 32-kilometer tunnel brings water from the Mohale reservoir to the Katse reservoir.

Before these two dams were constructed, Lesotho had to depend on South Africa. The country has now attained self-sufficiency in electric power generation. Future phases of the LHWP include construction of more dams, tunnels, and hydropower stations.


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