Wadi al-Rummah or ar-Rummah (ar: وادي الرمة) is one of the Arabian Peninsula's longest river valleys, at a length of almost 600 km (370 mi). Now mostly dry and partly blocked by encroaching sand dunes, the wadi rises near Medina at Jibāl al Abyaḑ (the White Mountain). It then runs northeast, joining several smaller wadis; among them are Mohalla Wadi and Murghala Wadi to the north and Jifn Wadi and Jarir Wadi to the south. It ends at the Thuayrat Dunes of the ad-Dahna Desert in Al-Qassim Province, near Buraidah.

The wadi then sinks beneath the sand dunes, where it is called Mistewy Wadi. It emerges on the other side of the desert as Wadi al-Batin (approx. 425 km (264 mi)), which continues towards the northeast and forms the western boundary of Kuwait. It empties finally into the Persian Gulf.

The valley is wide, for it was once a major river valley. According to Dr. Abdullah Al-Musnad from the University of Qassim, about 10,000 years ago it was a river flowing from Medina to the Persian Gulf, with a total length of 1,200 km (750 mi). Periods of drought and the movement of sand at Althwairat and Dahna led to the course of the valley being cut into three parts: Wadi al-Rummah (the longest, at 600 km (370 mi)), Wadi Aloddi (45 km (28 mi)), and Wadi al-Batin (450 km (280 mi)). Geological studies show that Wadi al-Rummah flows at full capacity about three times every 100 years. It flowed most recently in 1945, 1982, 1987, 2004, 2008 and 2018. In 1818, the river valley was flooded for 40 days, in 1838 for 22 days, in 1987 and 2008 for 17 days. In 1838 the wadi overflowed, creating a 200-square-mile (520 km) lake that persisted for two years and attracted water birds which had rarely been seen in the valley.

Farouk El-Baz piqued the interest of Biblical scholars around the world with his announcement of paleo-drainage from Arabian Peninsula into the Persian Gulf. The idea that a river once flowed across the deserts of Arabia, and somehow connected with the Tigris and/or Euphrates Rivers, draws its evidence from satellite datasets, especially from the radar images taken during the 1994 mission of the Space Shuttle Endeavour. El-Baz studied the images, and noticed that traces of a defunct river that emerged from Kuwait and crossed northern Arabia from west to east were visible beneath the sands, thanks to the ground-penetrating capabilities of the radar technologies.

He called it the Kuwait River, which is more popularly known as Wadi Al-Batin, an extension of Wadi Al-Rummah. The Wadi Al-Batin river system would have been responsible for deposition of the Dib DiBa Formation (similar to an alluvial fan deposit, both morphologically and sedimentologically). This river system may have been active 2500–3000 BC.

• List of wadis of Saudi Arabia

• Farouk El-Baz (Boston University), "A river in the desert", Discover, July 1993.

• countrystudies.us – Saudi Arabia: Topography and Natural Regions (Source: U.S. Library of Congress)
• youtube.com – Flow in November 2008 between Unaizah and Buraidah, Qassim province
• mekshat.com – Photo of 2008 flow

25°48′22″N 42°52′23″E / 25.80611°N 42.87306°E / 25.80611; 42.87306