wadis

Wadis are valleys or riverbeds that are dry for most of the year. The term comes from the Arabic wadi, meaning “valley” or “stream valley.” In arid and semi-arid regions, wadis contain water only after rain, and their channels may be largely empty except during episodic floods. They range from broad, flat-bottomed troughs to narrow, steep-sided gorges.

Formation and hydrology: Wadis are carved by episodic runoff from intense rainfall, and their channels can fill rapidly during flash floods that move large sediment loads. In some wadis, groundwater within the channel recharges aquifers, supporting occasional springs and riparian vegetation along the banks. Sediment deposited by flood events forms alluvial fans at the mouth or terraces along the channel.

Geographic distribution and examples: Wadis are common in North Africa and the Middle East, including the Sahara, the Arabian Peninsula, and the Levant. Notable examples include Wadi Rum in Jordan, Wadi Bani Khalid in Oman, and Wadi Musa near Petra.

Human use, ecology, and hazards: Wadis have historically served as travel routes and as sources of seasonal water for oases and agriculture in arid regions. They can support sparse desert ecosystems along their margins and sometimes host springs. Due to their propensity for sudden flash floods, wadis pose significant flood hazards to nearby settlements and infrastructure, making flood risk a key consideration in arid-land planning and development.