The Omo River (Amharic: ኦሞ ወንዝ, romanized: Omo Wenz; also called Omo-Bottego) is the largest river in southern Ethiopia that is not part of the Nile Basin. It flows entirely within Ethiopia and empties into Lake Turkana, which is located on the border between Ethiopia and Kenya. The river is the main water source for the Turkana Basin, a region that does not drain into the ocean.
The area around the river is well known for containing many early hominid fossils and archaeological discoveries, such as ancient stone tools. Because of these findings, the region was added to the UNESCO World Heritage List in 1980.
Geography
The Omo River forms where the Gibe River, the largest tributary of the Omo, and the Gojeb River, a large right-bank tributary, meet. Because of their size, length, and path, the Omo and Gibe rivers are sometimes thought of as the same river with different names. Because of this, the entire river basin is sometimes called the Omo-Gibe River Basin. This basin includes parts of the western Oromia Region and the middle of the Southern Nations, Nationalities, and People's Region.
The river generally flows south, but it makes a major turn westward near 7° N 37° 30' E to 36° E. From there, it turns south again until 5° 30' N, where it makes a large S-shaped bend before continuing south toward Lake Turkana. According to the Ethiopian Central Statistical Agency, the Omo-Bottego River is 760 kilometers (470 miles) long.
As it flows, the Omo-Bottego drops about 700 meters (2,300 feet) from the point where the Gibe and Wabe rivers meet at 1,060 meters (3,480 feet) to the lake level at 360 meters (1,180 feet). This drop makes the river fast in its upper parts, where it is broken by waterfalls like Kokobi. The river is only navigable for a short distance above where it flows into Lake Turkana, one of the lakes in the Gregory Rift. The Spectrum Guide to Ethiopia notes that the river is a popular spot for white-water rafting in September and October, when the river is high from the rainy season. The most important tributary of the Omo-Bottego is the Gibe River. Other tributaries include the Wabi, Denchya, Gojeb, Mui, and Usno rivers.
The Omo-Bottego River formed the eastern borders of the former kingdoms of Janjero and Garo. The river also flows near the Mago and Omo National Parks, which are known for their wildlife. Many animals live near and on the river, including hippos, crocodiles, and puff adders.
Archaeological findings
The Omo River basin is important for studying Earth's history and ancient human activity. More than 50,000 fossils have been found in the lower valley, including 230 fossils of early human relatives from the Pliocene and Pleistocene eras. Fossils from the Australopithecus and Homo genera have been discovered at several sites, along with tools made from quartzite. The oldest tools date back about 2.4 million years. At first, scientists thought these tools might belong to a type of tool-making older than the Oldowan industry found in the Olduvai Gorge. Later studies showed that the tools’ simple appearance was due to poor-quality materials, and their design fits within the Oldowan industry.
The first discoveries in the area happened in 1901 by a French expedition. More important finds were made between 1967 and 1975 by an international team. They uncovered items such as the jawbone of an Australopithecus, estimated to be about 2.5 million years old. Fossil remains of Olduwan hominids from the early Pleistocene and Pliocene eras were also found. Quartz tools were discovered near Homo sapiens remains along the riverbanks. Since then, excavations have been led by a team from France and the United States.
In addition to early human fossils, many fossils of mammals and fish have been found in the Omo Valley.
Human impact
The lower valley of the Omo is thought by some to have been a meeting place for many cultures and ethnic groups over thousands of years. This area is known for having many fossils of early humans. Today, the people living in the Lower Valley of the Omo, such as the Mursi, Suri, Nyangatom, Dizi, and Me'en, are studied because of their cultural differences.
Italian explorer Vittorio Bottego arrived at the Omo River on June 29, 1896, during his second trip to Africa (1895–1897). He died during this trip on March 17, 1897. The Omo River was later renamed Omo-Bottego to honor him. In 1898, Herbert Henry Austin and his team reached the Omo delta on September 12. They discovered that an Ethiopian group, led by Ras Wolda Giyorgis, had already placed Ethiopian flags on the northern shore of Lake Turkana on April 7. Lieutenant Alexander Bulatovich led another Ethiopian expedition that reached Lake Turkana on August 21, 1899. This trip caused damage, but some French members of the group mapped parts of the Omo River delta for the first time. This map of the river was used until the 1930s, when Italian colonial mapmakers created a more accurate version of the river and its delta.
Hydroelectric power stations
The Omo River basin includes several power stations and dams, such as those on the Gilgel Gibe River and Gibe River, which are smaller rivers that flow into the Omo River. Although the names of these power stations and dams may seem confusing, they are all located in the area of the Omo River.
The Gilgel Gibe II Power Station is a hydroelectric facility on the Omo River that produces 420 Megawatt (MW) of electricity. Water for the power station comes from a tunnel entrance on the Gilgel Gibe River, which is part of a system that uses river water directly for power generation. This tunnel is located downstream from the Gilgel Gibe I Dam, which is also on the Gilgel Gibe River. Together, these two structures form a series of hydroelectric projects.
The Gibe III Hydroelectric Dam is a large roller-compacted concrete dam, 243 metres (797 ft) tall, on the Omo River in Ethiopia. It is the largest hydropower plant in Ethiopia, producing about 1,870 MW of electricity. This output more than doubles Ethiopia’s total electricity capacity compared to its 2007 level of 814 MW. Some groups have raised concerns about the dam’s construction, with organizations opposing it due to potential negative effects on local communities. Terri Hathaway, director of International Rivers’ Africa program, described Gibe III as "the most destructive dam under construction in Africa." She stated that the project could harm half a million people in the region by increasing hunger and conflict. A group of international activists started an online petition to protest the dam over human rights issues.
Azeb Asnake, the project manager for Gibe III, said plans are in place to address any potential problems. Asnake also stated that the project would not cause harm and noted that many people in the area rely on food aid. He explained that the new power station is needed because only 25% of Ethiopia’s population currently has access to electricity.
2006 floods
In 2006, heavy rains caused the Omo River to flood its lower section, leading to the deaths of at least 456 people and leaving over 20,000 people stranded for five days, ending on August 16. Although heavy rains during this time of year are common in the region, overgrazing and deforestation are believed to have worsened the situation. A representative from the World Food Programme, Paulette Jones, explained that rivers in Ethiopia now hold less water than they did in the past because silt has filled them. This means even less intense rainfall can cause rivers to overflow. Seasonal flooding of the Omo River is important for the indigenous groups living along its banks. The flood deposits fertile silt and covers the riverbanks with water, allowing farming to take place. The many communities along the lower Omo River, including the Turkana, Dassanach, Hamer, Nyangatom, Karo, Kwegu, Mursi, Bodi, and Me'en, rely heavily on farming that happens after floodwaters recede. The large flood in 2006 was the only major flood recorded in the past fifty years. Recently, the water level in Lake Turkana has dropped, and this lake is generally recognized to receive about ninety percent of its water from the Omo River. This drop has already caused the lake's salt level to increase.