Trapping water in the soil Small structures capture runoff water for household use and crop-growing in Tunisia By Herman Verlodt
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Construction of majels
n the south of Tunisia, in zones with an annual rainfall of about 100 150 mm, jessours are used to capture runoff water and store it in the soil. The aim is to construct zones where about 300 - 350mm water is captured to allow for effective growing of fruit trees and thus generate economically significant yields and improve the income of households. The jessours are very sensitive during the first and second year after planting, and to ensure the survival of the trees and cattle, complementary water conservation structures are constructed to supply more water. These structures are called fesguias and majels.
Traditionally, in some regions of Tunisia and especially in the region of Zammour and Béni Kheddache, every household has at least one majel at their disposal. The volume of these reservoirs varies depending on the catchment area. However, on average, a catchment area covers an area of 200m², allowing collection of 20m3of water with one rain shower of 100mm. During very dry years, people may buy water and store it in the majel. The cost of construction of a majel depends on the volume, but is about €10 – 15 per cubic metre.1
Fesguias and majels
Construction of fasguias
Fesguias and majels are water reservoirs made in masonry in a soil excavation. Their storage capacity is variable but generally from 20 to 100m3. There are two versions – the first, mostly small, is for domestic drinking water while the second variety, mostly bigger, is for agricultural use. Reservoirs for domestic drinking water generally capture water from roofs or sometimes from a catchment made of masonry. These reservoirs also provide water for cattle and sometimes to an individual tree near the home or to a small garden. Reservoirs for agriculture collect water from a natural catchment. In this case, the reservoir is protected by at least one, sometimes two, decantation basins (silt traps), for disposal of erosion material carried by the water. This prevents clogging of the reservoir by sedimentation. The water stored in reservoirs for agriculture use is usually utilised for complementary irrigation of trees planted in jessours (generally during the first, and eventually, the second year). These reservoirs play a major role in successful implementation of jessour plantations, especially by allowing maximum survival after planting of trees in jessour terraces. As such, these reservoirs are mostly situated close to jessours.
Fesguias have a rhomboid form (see figure). Their storage capacity is in general around 90 - 100m3, but sometimes more, depending on the catchment area and physical situation. Their construction cost is around €20 per cubic metre.
Fig 1: View of transversal section of a fesguia (above) and a majel (below). Note that both have a constructed (masonry) catchment area.
1. Silt trap 2. Water storage reservoir 3. Opening for manual exhaust of water 4. Catchment surface 5. Catchment boundaries 6. Surrounding soil level
General view of a majel. The hole at the bottom of the photo is a silt trap; while at the top is the covering of the underground reservoir and the opening for manual extraction.
Miti October-December 2011
The writer is a former professor of the University of Tunis, Tunisia and a researcher specialising in horticulture and irrigation techniques Email: herman.verlodt@gnet.tn or h.verlodt@yahoo.fr 1
One Euro is currently worth Ksh130, so this is Ksh1,300 to 1,950 per cubic metre. For a majel of 20m3, the cost then is Ksh 26,000 - 39,000.
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