{{Short description|Hydrological feature}} {{Other uses}} {{More citations needed|date=April 2018}} {{Use dmy dates|date=November 2021}}
[[File:18 Wadi Ghuweir Trail to Feynan - In the Oasis - panoramio.jpg|thumb|Wadi Ghuweir Trail to Feynan, Jordan]]
A '''wadi''' ({{ipac-en|ˈ|w|ɒ|.|d|i}} {{respell|WOD-ee}}; {{langx|ar|وَادِي|}}) is a river valley or a wet (ephemeral) riverbed that contains water only when heavy rain occurs. Wadis are located on gently sloping, nearly flat parts of deserts; commonly they begin on the lowest portions of alluvial fans and extend to inland sabkhas or dry lakes. Permanent channels do not exist, due to lack of continual water flow. Water percolates down into the stream bed, causing an abrupt loss of energy and resulting in vast deposition. Wadis may develop dams of sediment that change the stream patterns in the next flash flood.
Wadis tend to be associated with centers of human population because sub-surface water is sometimes available in them. Nomadic and pastoral desert peoples will rely on seasonal vegetation found in wadis, even in regions as dry as the Sahara, as they travel in complex transhumance routes.
The centrality of wadis to water – and human life – in desert environments gave birth to the distinct sub-field of wadi hydrology in the 1990s.<ref>[http://www.jeunessearabe.info/article.php3?id_article=98?lang=fr Review of Wheater, Howard; Al Weshah, Radwan, Hydrology of Wadi systems -IHP Regional Network on Wadi Hydrology in the Arab Region] {{Webarchive|url=https://web.archive.org/web/20090724180712/http://www.jeunessearabe.info/article.php3?id_article=98%3Flang%3Dfr |date=24 July 2009 }}, UNESCO – Technical documents in hydrology vol 55, SC.2002/WS/33,(2002).</ref>
==Etymology== The word 'wadi' is very widely found in Arabic toponyms. Some Spanish toponyms are derived from Andalusian Arabic where wadi was used to mean a permanent river,{{citation needed|date=March 2016}} for example: Guadalcanal from ''wādī al-qanāl'' ({{langx|ar|وَادِي الْقَنَال}}, "river of refreshment stalls"), Guadalajara from ''wādī al-ḥijārah'' ({{langx|ar|وَادِي الْحِجَارَة}}, "river of stones"),<ref>Ayuntamiento de Guadalajara, [http://www.guadalajara.es/recursos/doc/Turismo/Guias/32521_2222201291352.pdf Guadalajara tourist guide, p.5.] {{webarchive|url=https://web.archive.org/web/20120701172107/http://www.guadalajara.es/recursos/doc/Turismo/Guias/32521_2222201291352.pdf |date=1 July 2012 }}, retrieved 17 August 2013</ref> or Guadalquivir, from ''al-wādī al-kabīr'' ({{langx|ar|اَلْوَادِي الْكَبِير}}, "the great river").
==Sediments and sedimentary structures== left|thumb|Wadi Degla in Egypt during the dry season
In basin and range topography, wadis trend along basin axes at the terminus of fans. They have braided stream patterns because of the deficiency of water and the abundance of sediments. Wadi sediments may contain a range of material, from gravel to mud, and the sedimentary structures vary widely. Thus, wadi sediments are the most diverse of all desert environments.
Flash floods result from severe energy conditions and can result in a wide range of sedimentary structures, including ripples and common plane beds. Gravels commonly display imbrications, and mud drapes show desiccation cracks. Wind activity also generates sedimentary structures, including large-scale cross-stratification and wedge-shaped cross-sets. A typical wadi sequence consists of alternating units of wind and water sediments; each unit ranging from about {{convert|10|–|30|cm|in|0|abbr=on}}. Sediment laid by water shows a complete fining upward sequence. Gravels show imbrication. Wind deposits are cross-stratified and covered with mud-cracked deposits. Some horizontal loess may also be present.
Wind also causes sediment deposition. When wadi sediments are underwater or moist, wind sediments are deposited over them. Thus, wadi sediments contain both wind and water sediments.
==Hydrological action== [[File:Triassic wadi deposit Ogmore.jpg|thumb|Triassic wadi deposit near Ogmore-by-Sea, Wales. Clasts are carboniferous limestone.]]
Modern English usage differentiates wadis from canyons or ''arroyo'' (Spanish, used in the Americas for similar landforms)<ref>{{cite web |title=Arroyo Definition |publisher=MSN Encarta |access-date=2009-10-02 |url=http://encarta.msn.com/dictionary_/arroyo.html |archive-url=https://web.archive.org/web/20090406213157/http://encarta.msn.com/dictionary_/arroyo.html |archive-date=2009-04-06 |url-status=dead }}</ref> by the action and prevalence of water. Wadis, as drainage courses, are formed by water and are distinguished from river valleys or gullies in that surface water is intermittent or ephemeral. Wadis are generally dry year round, except after a rain. The desert environment is characterized by sudden but infrequent heavy rainfall, often resulting in flash floods. Crossing wadis at certain times of the year can be dangerous as a result.
===Deposits=== Deposition in a wadi is rapid because of the sudden loss of stream velocity and seepage of water into the porous sediment. Wadi deposits are thus usually mixed gravels and sands. These sediments are often altered by eolian processes.<ref>{{cite journal|last1=Achite|first1=Mohamed|last2=Ouillon|first2=Sylvain|title=Suspended sediment transport in a semiarid watershed, Wadi Abd, Algeria (1973–1995)|journal=Journal of Hydrology|date=September 2007|volume=343|issue=3–4|pages=187–202|doi=10.1016/j.jhydrol.2007.06.026|bibcode=2007JHyd..343..187A}}</ref>
Over time, wadi deposits may become "inverted wadis", where former underground water caused vegetation and sediment to fill in the eroded channel, turning previous washes into ridges running through desert regions.
==Gallery== {{gallery|mode="packed" |File:Haid al-Jazil.jpg|Haid al-Jazil in Wadi Dawan, Yemen |File:Wadi Bani Khalid East RB.jpg|Wadi Bani Khalid in the Northern Governorate of Ash-Sharqiyyah Region, Oman,<ref name="OmanTripper2013">{{cite web|author=Alimsk|title=Wadi Bani Khalid & Wadi Hawer| website= omantripper.com | publisher= Oman Tripper|url=https://www.omantripper.com/wadi-bani-khalid/|date=2013-12-20| access-date= 2018-03-25}}</ref><ref name= "Pedro">{{cite web| author=Pedro|title= Visiting Wadi Bani Khalid, Oman: A Desert Paradise|date=5 September 2014 | website= travelwithpedro.com |publisher=Travel With Pedro| url=https://www.travelwithpedro.com/visiting-wadi-bani-khalid-oman-desert-paradise/|access-date=2018-03-25}}</ref> Arabian Peninsula ||File:DSC 0283 غوفي بلدية غسيرة دائرة تكوت ولاية باتنة.jpg|Abiod Valley in Algeria |File:NachalParan1.jpg|Wadi in Nahal Paran, Negev, Israel |File:Oued Tissint.jpg|Oued Tissint, Morocco |File:Dry riverbed and basalt columns (Namibia).jpg|Dry fluvial channel cutting through columnar basalt in Namibia |File:Al Bithnah Fort viewed from the Wadi Ham.jpg|The Al Bithnah Fort in the Wadi Ham, United Arab Emirates |File:Wadi Shawka looking North.jpg|The Wadi Shawkah in the United Arab Emirates |File:Wadi Lajab 2.jpg|Wadi Lajab in Jazan, Saudi Arabia |File:Wadi East Egypt.jpg|Wadis in northeastern Egypt |Wadi, Socotra Island (14495206039).jpg|A wadi in Socotra, Yemen }}
==See also== {{div col}} * {{annotated link|Desert pavement|Alluvial desert}} * {{annotated link|Arroyo (watercourse)}} * {{annotated link|Canyon}} * {{annotated link|Coulee}} * {{annotated link|Gulch}} * {{annotated link|Gully}} * {{annotated link|Intermittent river}} * {{annotated link|Oasis}} * {{annotated link|Valley of Tuwa|''Wād Ṭuwā''}} in the Sinai peninsula, holy Muslim site {{div col end}}
==References== {{Reflist}}
===Bibliography=== {{refbegin}} *{{cite web |archive-url=https://web.archive.org/web/20030509022503/http://www.tec.army.mil/research/products/desert_guide/lsmsheet/lswadis.htm |archive-date=9 May 2003 |url=http://www.tec.army.mil/research/products/desert_guide/lsmsheet/lswadis.htm |title=Summary: Drainage Courses, Wadis |publisher=United States Army Corps of Engineers. Desert Processes Working Group; Knowledge Sciences, Inc. |date= |access-date=26 August 2008 }} *{{cite web |archive-url=https://web.archive.org/web/20030509021836/http://www.tec.army.mil/research/products/desert_guide/lsmsheet/lsinver.htm |archive-date=9 May 2003 |url=http://www.tec.army.mil/research/products/desert_guide/lsmsheet/lsinver.htm |title=Summary: Drainage Courses, Wadis – Inverted |publisher=United States Army Corps of Engineers. Desert Processes Working Group; Knowledge Sciences, Inc. |date= |access-date=26 August 2008 }} *{{cite book |last=Glennie |first=K. W. |year=1970 |title=Deserts sedimentary Environments |series=Developments in Sedimentology |volume=14 |publisher=Elsevier |location=Amsterdam |isbn=0-444-40850-9 }} {{refend}}
==External links== {{Commons category|Wadis}} {{wiktionary}} * [http://www.unesco.org/water/ihp/wadi.shtml IHP REGIONAL WADI HYDROLOGY NETWORK], International Hydrological Programme, UNESCO. * [https://web.archive.org/web/20090404004918/http://www.acsad.org/Departments.asp?depid=2 Arab Center for Studies of Arid Zones and Dry lands (ACSAD)]: Water resources division.
{{Rivers, streams and springs}} {{Authority control}}
01 Category:Dry or seasonal streams Category:Canyons and gorges Category:Fluvial landforms Category:Valleys Category:Arabic words and phrases