Wadi Howar is a wadi

Wadi

Wadi is the Arabic term traditionally referring to a valley. In some cases, it may refer to a dry riverbed that contains water only during times of heavy rain or simply an intermittent stream.-Variant names:...

 in Sudan

Sudan

Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...

 and Chad

Chad

Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...

. It travels approximately 400 kilometres in a northeasterly direction from the Ouaddaï highlands

Ouaddaï highlands

Ouaddaï Highlands is an area in east of Chad along the border with Sudan. The Ennedi Plateau and the Ouaddaï highlands in the east of Chad complete the image of a gradually sloping basin, which descends towards Lake Chad...

 in Chad across the North Darfur

North Darfur

North Darfur is one of the 15 wilayat or states of Sudan. It is one of the three states composing the Darfur region. It has an area of 296,420 km² and an estimated population of approximately 1,583,000 . Al-Fashir is the capital of the state...

 state of Sudan, before losing itself in the Libyan Desert

Libyan Desert

The Libyan Desert covers an area of approximately 1,100,000 km2, it extends approximately 1100 km from east to west, and 1,000 km from north to south, in about the shape of a rectangle...

. Towards its western end it forms a part of the international boundary between Sudan and Chad, separating the West Darfur

West Darfur

West Darfur is one of the 15 states of Sudan, and one of three comprising the Darfur region. It has an area of 79,460 km² and an estimated population of approximately 1,007,000 . It borders North and South Darfur to the east. The Chadian prefectures of Biltine and Ouaddaï lie to the west,...

 state of Sudan and the Borkou-Ennedi-Tibesti Region of Chad.

The wadi is the remnant of the ancient Yellow Nile, a tributary of the Nile

Nile

The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. It is long. It runs through the ten countries of Sudan, South Sudan, Burundi, Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Ethiopia, Uganda and Egypt.The Nile has two major...

 from about 8000 to 1000 BCE. It met the Nile near the southern point of the Great Bend.