Wadi

A wadi is a valley or ravine that is dry for most of the year but can carry water when heavy rain falls. The term comes from Arabic "waadi" (وادي), meaning valley or ravine. Equivalent terms in other languages include "oued" (French) and "wadi" (English).

Wadis are commonly found in arid and semi-arid regions of North Africa, the Middle East, and East Africa. In Somalia, some seasonal ravines have characteristics similar to wadis, with water flowing during the Gu (spring) and Deyr (autumn) rainy seasons.

Formation

A wadi forms through the prolonged flow of water over time. When heavy rain falls suddenly, the hard, dry ground cannot absorb water quickly, so the water rushes into low-lying areas and carves out a wide channel. Rocks and sediment carried by the water accumulate at the bottom of the valley.

Flash floods

The most dangerous feature of wadis is the flash flood. Rain falling in distant, elevated areas can cause a sudden wall of water to surge through a wadi unexpectedly, even if the sky above the wadi is clear. For this reason, settlements or camps located in wadis are considered hazardous.

Human uses

People in arid regions use wadis in various ways: drilling wells in the sediment beneath the valley, watering livestock, seasonal cultivation, and as passage routes for travel. Some wadis have small dams built in them to store water or return it to the soil.