Wadi, alternatively wād, is the Arabic term traditionally referring to a valley. In some instances, it may refer to a dry riverbed; the term wādī is widely found in Arabic toponyms. Some Spanish toponyms are derived from Andalusian Arabic where wādī was used to mean a permanent river, for example: Guadalcanal from wādī al-qanāl, Guadalajara from wādī al-ḥijārah, or Guadalquivir, from al-wādī al-kabīr. Wadis are located on sloping, nearly flat parts of deserts. In basin and range topography, wadis trend along basin axes at the terminus of fans. Permanent channels do not exist, due to lack of continual water flow. Wadis have braided stream patterns because of the deficiency of water and the abundance of sediments. Water percolates down into the stream bed, causing an abrupt loss of energy and resulting in vast deposition. Wadis may develop dams of sediment. Wind causes sediment deposition; when wadi sediments are underwater or moist, wind sediments are deposited over them. Thus, wadi sediments contain both water sediments.
Wadi sediments may contain a range of material, from gravel to mud, the sedimentary structures vary widely. Thus, wadi sediments are the most diagnostic 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 display imbrications, mud drapes show desiccation cracks. Wind activity generates sedimentary structures, including large-scale cross-stratification and wedge-shaped cross-sets. A typical wadi sequence consists of alternating units of water sediments. Sediment laid by water shows complete fining upward sequence. Gravels show imbrication. Wind deposits are covered with mud-cracked deposits; some horizontal Loess may present. Modern English usage differentiates wadis from canyons or washes by the action and prevalence of water. Wadis, as drainage courses, are formed by water, but are distinguished from river valleys or gullies in that surface water is intermittent or ephemeral.
Wadis are dry year round, except after a rain. The desert environment is characterized by sudden but infrequent heavy rainfall resulting in flash floods. Crossing wadis at certain times of the year can be dangerous as a result. 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 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. 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 mixed gravels and sands; these sediments are altered by eolian processes. 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.
Summary: Drainage Courses, Wadis. United States Army Corps of Engineers. Desert Processes Working Group. Summary: Summary: Drainage Courses, Wadis - Inverted. United States Army Corps of Engineers. Desert Processes Working Group. Developments in Sedimentology, v.14. Elsevier, Amsterdam, 222p. IHP REGIONAL WADI HYDROLOGY NETWORK, International Hydrological Programme, UNESCO. Arab Center for Studies of Arid Zones and Dry lands: Water resources division
Michel Bernard is a French writer and senior official. A graduate from the École nationale d'administration in 1992, he made a career in the prefectural corps. 1999: Mes tours de France. Éditions L'Âge d'Homme. ISBN 2-8251-1276-3. 2003: Comme un enfant. Le Temps qu'il fait. ISBN 2-86853-370-1. 2003: Jean-Marie Lecomte. Le Ciel entre les feuilles. Éditions Noires terres. ISBN 2-915148-02-3. 2004: Jean-Marie Lecomte and Marc Paygnard. La Meuse sentimentale. Éditions Noires terres. ISBN 978-2-915148-03-9. CS1 maint: uses authors parameter 2007: La Tranchée de Calonne. La Table ronde. ISBN 978-2-7103-2981-7. Prix Erckmann-Chatrian 2007 2009: La Maison du docteur Laheurte. La Table ronde. ISBN 978-2-7103-3077-6. Prix Maurice Genevoix 2009 2010: Le Corps de la France. La Table ronde. ISBN 978-2-7103-6553-2. Prix littéraire de l'armée de terre - Erwan Bergot 2010 2011: Pour Genevoix. La Table ronde. ISBN 978-2-7103-6879-3. 2014: La Grande Guerre vue du ciel. Éditions Perrin. ISBN 978-2-262-04071-0. 2015: Les Forêts de Ravel.
La Table ronde. ISBN 978-2-7103-7607-1. Prix du festival Livres & Musiques de Deauville 2015 2016: Visages de Verdun. Perrin. ISBN 978-2-262-04813-6. 2016: Deux remords de Claude Monet. La Table ronde. ISBN 978-2-7103-8070-2. 2008: Robert Porchon. Carnet de route. La Table ronde. ISBN 978-2-7103-3083-7. 2011: Maurice Genevoix. La Mort de près. La Table ronde. ISBN 978-2-7103-6882-3. 2013: Maurice Genevoix. Correspondance: 28 août 1914-30 avril 1915. La Table ronde. ISBN 978-2-7103-7055-0. 2013: Maurice Genevoix. Ceux de 14. Flammarion. ISBN 978-2-08-130985-2. 2016: André Pézard. Nous autres à Vauquois. La Table ronde. ISBN 978-2-7103-7966-9. Michel Bernard on Babelio Le nouveau sous-préfet de L’Haÿ-les-Roses est un écrivain multi-primé on Le Parisien Michel Bernard on France Inter Michel Bernard on Le Choix des libraires Michel Bernard, Les Forêts de Ravel on Éditions de la Table ronde Michel Bernard: un haut-fonctionnaire et écrivain sous-préfet de L’Haÿ-les-Roses on 94 citoyens
The Thomson Dam is a major earth and rockfill embankment dam with a controlled chute spillway across the Thomson River, located about 130 kilometres east of Melbourne in the West Gippsland region of the Australian state of Victoria. The impounded reservoir is called Thomson Reservoir, sometimes called Lake Thomson; the dam is located near the former township of the Baw Baw National Park. Despite opposition from conservationists and farmers, plans for the dam were approved in late December 1975 to provide Melbourne with water security. A dam on the Thomson River was preferred because the river had a large flow, high water quality and was elevated high enough to provide water to the upper Yarra system by gravity flow. Early work in the early 1970s saw construction of a 19 kilometres long tunnel through the Thomson Yarra divide to allow water from the Thomson River to flow into the Upper Yarra Reservoir. Work on the dam itself commenced in 1976 and the dam wall was ready to contain water by 1983.
The tunnel, located at the northern end of the reservoir, allows water to be transferred west to Upper Yarra Reservoir and on to Silvan Reservoir for distribution as drinking water in Melbourne. Downstream releases from Thomson Reservoir pass through a 7.4 MW hydro power plant, at the base of the dam which generates electricity and feeds it into the state power grid. Between 1997 and 2011, drought depleted much of the reservoir's water. In early January 2006, the Thomson Dam was at 45.4%. While there were minor rises in water levels the Thomson Dam reached its all-time low of 16.2% on 3 July 2009. Heavy rainfall in 2010 and 2011 has increased Melbourne's water storages to levels not seen for ten years; the Thomson Dam by the end of 2011 had reached 54.4 % full. The last time the reservoir was full and spilling was in the spring of 1996; the Thomson Dam is managed by Melbourne Water. Thomson Reservoir Fact Sheet Lowdown on the Thomson Reservoir - The Age, 5 June 2003 Crunch time today for Thomson Dam - The Age, 13 December 2006'Drought-proof' dam hits record low level