Water under the sand
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CTA. 1994. Water under the sand. Spore 53. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/49487
As incredible as it might seem just below the sand dunes of Mauritania (at a depth of only 50-150cm) there is natural moisture. A research worker at the the Institut des Regions Arides de Tunisie (Institute for the arid regions of Tunisia) has...
As incredible as it might seem just below the sand dunes of Mauritania (at a depth of only 50-150cm) there is natural moisture. A research worker at the the Institut des Regions Arides de Tunisie (Institute for the arid regions of Tunisia) has developed a simple method of reafforestation which makes use of this moisture. In a region with a rainfall of less than 300mm per annum it would not appear possible for sand to remain moist. However, the explanation for the phenomenon is relatively simple. Since bare sands are poor conductors of heat, only the sand near the surface is heated and evaporation is thus limited. Furthermore, there is a layer of dry sand between the surface of the soil and the lower layer of residual moisture. This layer of dry sand acts as a protective mulch. It cuts off the flow through capillary action and, as a result, also prevents evaporation. The combined effect of these two phenomena demonstrates how sands without vegetation can preserve rainwater for several years. This mulch, or shallow layer of dry sand, can be 'broken'. All that is needed is a bottomless metal cylinder with a cutting edge. This cylinder is driven into the sand and then watered abundantly. The water is guided by the walls of the cylinder and flows straight down, thus restoring contact between the lower layer of moisture and the surface of the soil. The roots of young trees can begin their growth in the moistened section of the cylinder and subsequently reach the lower layer of residual moisture. As a result, they become self-supporting and do not require irrigation. Prosopis juliflora plants were established using this method seven years ago and are still alive, despite extremely low rainfall. Houcine Khatteli, Institute des Regions Arides, Route de Djoff, km22 - 4119 Medenine, TUNISIA