Wadi Halfa, town, N Sudan, on Lake Nasser. It is the terminus of a railroad from Khartoum and is the point at which cotton, wheat, livestock, and other goods are transferred to steamers going down the Nile into Egypt. Archaeological expeditions have worked to excavate and preserve the area's numerous Egyptian antiquities, which faced flooding from the reservoir of the Aswan High Dam. Founded in the 19th cent., Wadi Halfa became (1885-98) the headquarters of the Anglo-Egyptian army as it prepared to reconquer Sudanese territory from the Mahdi. The railroad up the Nile to Wadi Halfa was built to support Lord Kitchener's forces during the reconquest. During World War II, the town served as a staging post on the Allied communication line with Egypt via central Africa.

Wadi (وادي ) (also: Vadi) is traditionally a valley. In some cases it can refer to a dry riverbed that contains water only during times of heavy rain. Compare arroyo (creek), canyon, gulch, wash and gully.

The term is very widely found in Arabic toponyms. Wadis tend to be associated with centers of human population because sub-surface water is sometimes available in wadis.

Crossing wide wadis at certain times of the year can be dangerous, because of unexpected flash floods. Such flash floods cause many deaths each year in Saudi Arabia and many other Middle Eastern countries.

In North Africa the transcription oued is used. In southwestern Africa, the term rivier is used, which is the Afrikaans word for "river". The Hebrew term nahal (נחל)and Hindi/Urdu term "Nala" is synonymous in meaning and usage.

Some names of Spanish rivers are derived from Andalusi Arabic toponyms where was used to mean a permanent river, for example Guadalcanal, Seville or Guadalquivir from al-wādī al-kabīr = "the great river".

Wadi deposits

Wadis are the streams in a desert environment and generally are dry year round except after a rain. The desert environment is characterized by a sudden but frequent heavy rainfall. As rainfall occurs near hill ranges, wadis usually form near a hilly terrain. The deposition of wadi is rapid because of the sudden loss of the velocity and absorption of the water into the ground. Fluvial activity in a desert environment is also characterized as flash floods.

Other references

Job speaks of his friends whom he calls brothers as being like these wadis. The Jewish Study Bible transliterated the word "brook" in for the word "wadi". The commentator notes, "Wadi, a seasonal stream that may be dangerously overflowing in winter and dry in summer". Albert Barnes (1798–1870), in his commentator books notes, "The idea here is, that travelers in a caravan would approach the place where water had been found before, but would find the fountain dried up or the stream lost in the sand; and when they looked for refreshment, they found only disappointment. The reference to this verse is found in where it reads that confidence in a treacherous person, an unfaithful person, is like a broken tooth and a foot out of joint." Barnes points to their ineffectiveness rather than emphasizing the pain caused by the two ailments.