How are wadis formed in desert regions?

Wadis are ephemeral watercourses found in desert regions that typically remain dry but flow during periods of heavy rain. They are primarily formed by the intermittent action of running water, which is more effective at shaping the desert landscape than wind erosion.1

Many wadis are remnants of ancient river systems that were active during the Pleistocene Epoch. During that period, these rivers carried vast amounts of sediment from the interior toward lower-lying areas, creating extensive deltas and drainage channels.1

While these channels are often dry today, they can still experience destructive floods during infrequent heavy rainfall. When these watercourses enter large expanses of sand, they lose their distinct identity as the alluvium they carry is redistributed by the wind.1