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Savoirs locaux et agriculture durable au Yémen

Frédéric Pelat
Amin Al-Hakimi


The effect of modern technologies on traditional soil and water conservation techniques in Shabwa and Hadramawt

Mohammed Aidrus Ali et Helen Lackner

Texte intégral

1Transformation of Yemeni agriculture during the second half of the 20th century took place at a rapid pace under the influence of a number of internal and external factors. Change had remained very slow under the Yemeni Imamate and during the first decade of the Republic. In the Yemen Arab Republic from the late 1970s onwards agriculture was transformed at remarkable speed due primarily to the rapid expansion of well irrigation agriculture. Most of this was financed by short-term emigrants to Saudi Arabia who thus hoped to ensure their future economic well-being at home by transforming their farms into modern units with assured water supplies. Well irrigation rapidly covered large areas which had previously contained rainfed and spate-irrigated fields, and allowed a transfer from subsistence crops (sorghum, etc.) to the cultivation of high value cash crops, qat in particular. By the late 1980s this mining of the water table had started to have serious negative impact in some areas as the aquifers dried up.

2In the Aden Protectorates, changes in agricultural practices and technologies started earlier, in the 1950s, as British technical advisers were sent to various protectorates to assist their rulers in raising revenue through economic development. It was at this time that the major modern spate irrigation schemes were built in Tuban, Abyan and Mayfac Hajr (in coastal Hadramawt). In less favored areas, such as Bayhan and elsewhere in what is now Shabwa Governorate, intervention was more modest, and most change took place after independence. A number of major interventions in agriculture occurred throughout the People's Democratic Republic of Yemen (PDRY) during the 1970s; these interventions were financed by the Soviet Union, the International Development Association of the World Bank (IDA), the International Fund for Agricultural Development (IFAD) and other multilateral agencies such as the Arab Fund for Economic and Social Development, the Islamic Development Bank, etc. While these projects focused primarily on the more productive areas of Lahj, Abyan, and Wādī Hadramawt, there were also some interventions in more remote areas, such as Bayhan. This paper will focus primarily on changes which took place in Shabwa Governorate, with examples from other areas, in particular Hadramawt; the paper’s theme is the impact of 'modern' imported technologies, equipment and approaches on indigenously developed ones.

Traditional and modern spate flow control structures

Traditional structures

3Throughout Yemen over the millennia, populations have developed techniques to divert the sudden and violent flows of seasonal rains towards cultivated lands, and also to protect their homes and fields from flood (called sayl in Arabic and spate in English) damage. In Shabwa these structures have traditionally been built of dry stone not 'bound' together with lime or other binding material as has been the case in Wādī Hadramawt in the last 400 years or so (Plate 1). Traditional diversion/protection structures are illustrated in Plates 1-3, which come from Bayhan and Wādī Hadramawt.

4There are four main types of diversion/protection structures in Bayhan:

  • Al-cijlamah (Plate 3) is a cone-shaped structure, with a circular base 3-4 m in diameter and a sharp conical point, usually standing 2-3 m. high with sides sloping 35-45º. The exterior surface of the structure contains no holes or cavities, being completely filled with small stones and pebbles so as to control erosion along a stretch of canal. As they are built at the canal dike, when the spate arrives erosion is prevented at the location of the structure in the dike. This structure is also used as a gryon (flow repellant structure) or spur to divert floods from wādī banks.
  • Al qayd (Plate 4) is a structure which diverts spate water into a main canal from the main wādī. The structure extends from the main spate canal to the center of the wādī at an acute angle with respect to the wādī flow. The height of the structure varies gradually from zero in the center of the wādī to the height of the spate canal. The foundation—usually deep and made of interlocking stones—rises gradually to form a triangular prism so that the drag force on the structure is minimal.
  • Al maseh is a form of retaining wall designed to protect vulnerable wādī banks. It is built from rounded stones, the gaps between stones filled with stones of smaller sizes to prevent direct contact between flowing water and the wādī banks. The structures commonly deviate from vertical by 30-45º. Stones used in construction are usually laid to make a smooth surface, to minimize the tangential flood force on the structure.
  • Al-macdhar or al-maskhal, a spillway for overflow, is made of dry masonry and covered with earth. When the command area has received sufficient water, farmers make a breach in the earth to let the water flow. These structures are placed at a point where the water will return to the main wādī bed for downstream users ; they can also be used as a fuse bund.

5A canal may have a qayd, cijlamah and at its command area a macdhar.

6In Wādī Hadramawt there are similar structures built of dry masonry and bound with lime. One famous structure is the Mouzza Shibām which is about 730 m long and 3 m high and built from stone bound with lime, and nughra (a mountain clay). Another type which is also common is called in Hadramawt a marsad: it is a structure that divides the spate flow between more than one canal.

7Throughout Yemen there are many types of structures serving similar purposes. They may have different names but share the fact that they are built of locally available materials and are designed and constructed with local expertise and experience. These structures are used to divert water flow onto fields, and to protect fields, wādī banks and homes from floods.

Recent changes

8In most wādīs there used to be series of small spate canals. In the past 40 years, government supported projects have financed and organized the construction of a few larger spate structures and weirs with redistribution canals, to replace the many smaller ones built on the traditional pattern. In other words, along a wādī where there had previously been many (10 or so) smaller off-takes and series of water diversion canals, a modern scheme would introduce one major weir with more engineered canals to supply the same or a larger command area.

9Gabion boxes, a galvanized iron wire frame filled with stones to make a structure of variable shape (Plate 5), were systematically introduced during the 1960s and 1970s as part of modern projects supported by multilateral and bilateral agencies. These projects were designed mostly by foreign engineers who spent short periods in Yemen and who had no time to discover or to study the advantages of the traditional structures. These engineers tended on the whole to believe that 'modern' industrial technology was by definition better than the traditional, and they designed projects on that basis. Local engineers trained at home or abroad largely accepted this approach. Most engineers preparing projects favored modern technology and designed diversion weirs and gabion structures, rather than focusing their energies on improving and modifying traditional structures. Another reason why engineers have shown a preference for the construction of larger weirs is that these structures are easier to design, are less “fiddly,” and were originally believed to be more effective.

10People got into the habit of relying on 'modern' gabions and failed to maintain and develop the traditional spate protection structures. People changed technology not because they believed that the new methods were better but primarily because the new methods were financed or heavily subsidized by the state or by a project. State subsidy or financing was a new development that had started during the Protectorates and was continued by the post-independence state. In the past farmers and communities had financed their own protection works and spate flow control works, but now that facilities could be subsidized by the state farmers were only too willing to give up the hard work and cost of these activities. Subsidies and nationalization of land in the former PDRY were both factors that led to the weakening or disintegration of community organizations necessary for construction of traditional structures.

11Thus many of the traditional structures stopped being used, and new modern designs were constructed alongside them, making the former less relevant. Today we can thus see “modern” structures built alongside traditional ones, both types operating simultaneously.

12Although they have some advantages, as seen in Table 1, the modern structures allow large amounts of spate water to gather into a single canal during each flood. The structures are often unable to control heavy floods, resulting in more severe damage to arable land and to wādī banks. This is a case of a modern innovation having a long-term negative impact—the traditional structures made more effective use of the water while also preserving topsoil and wādī banks from erosion. With respect to erosion control, the experience of recent decades has shown that a larger number of smaller structures are more stable and durable than are a few larger ones in the delicate environmental conditions prevalent in Yemen. Local experts in traditional construction believe that the small spate canals are more effective at weakening the spate flow energy and thus minimising flood damages.

Efforts to preserve and modernise the construction of the traditional structures

13The Wādī Bayhan Agricultural Development Project (1982-88, IFAD loan 68YD and IDA credit 1145 Yemen) is an example of good interaction between traditional and modern techniques. The project completed the construction of 40 000 cubic meters of spurs and gryons with gabions in Wādīs Bayhan and cAyn. When the planned number of gabions had been built, project management obtained the agreement of IFAD and IDA to use unspent funds to assist the people to rehabilitate and build traditional structures. The project helped farmers by paying a subsidy of up to YD (Yemeni Dinars) 500 (equivalent to USD 1500) per structure, as well as by financing the transport of rocks and stones. About 4 000 cubic meters of structures were built in this way, about 10% of the gabion volume.

14The project assisted the population in building canal intakes, spillways, spurs or gryons in bigger and sturdier versions of traditional designs. It was possible to use larger rocks because they were moved and put in place with front-end loaders capable of carrying far greater weights than possible with traditional methods. Traditionally such structures would have been built with smaller stones because of the difficulty of carrying heavy items to the top of the structures. These 'modernised traditional structures' are also of better quality because the work was done combining traditional and modern technology: the structures were founded directly on hard formations or, in the absence of a solid formation, their foundations were extended well below the expected scour depth as estimated by the engineers (e.g., if the scour was expected to be 1.5 m, the structure would go to 2 m).

15The technicians involved the project included a civil engineer and a foreman who did not have experience in traditional systems but who were open-minded. The farmers told them about the kind of structures they wanted and they discussed dimension, slope, and shape to reduce resistance to flow. None of the structures built are rectangular; instead all are designed to give a smooth face to the flow without any angles on which water or debris might be caught (Plate 3).

16This example shows how modern technology in the form of heavy equipment (excavators, front-end loaders) and subsidies can have a positive impact on spate structures built on the traditional pattern from dry masonry: the larger stones moved by front-end loaders helped to create structures traditional in concept but capable of withstanding heavier floods than purely traditional structures made of smaller rocks. Building according to the traditional method with minor improvements is also being currently implemented in Wādī Hadramawt by the Southern Governorates Rural Development Project (SGRDP) (Plate 6).

17The 1982 flood was one of the worst in the history of Bayhan. While many structures were washed out above ground, their foundations held strong. If they had been built with gabions they would have been completely washed out, as was the case for these structures built earlier. The project’s structures are still around and we believe that they will last for many decades to come. Due to good design, even the gabions built by the project still exist today. Their effectiveness is evident in the growth a tree-cover that sometimes obscures the gabions themselves, following the stabilisation of the wādī bed and sedimentation between the structures.


18Although we have discussed in detail only one type of flood control structure, we believe that its development is a good example of a number of important points that are generally valid in Yemen and elsewhere. Specifically, modern innovations can help to improve traditionally developed designs. However, this is the case only when innovations are introduced with care, after taking into consideration all the positive features of the traditional design. In this way innovations can be used to improve what can be improved while retaining the positive features of the traditional design. In this case the use of heavy machinery to add larger rocks to traditional structures was a positive innovation, as it did not change the fundamental design. Replacement of the numerous small structures with a few larger modern ones has been a failure. It ignored the advantages of the smaller structures (greater water and silt retention capacity, and weakening violent flows), and replaced traditional methods with imported designs and materials unsuited to local climatic and topographical conditions. Replacing traditional designs with modern ones should only be done with considerable care, and only after detailed study and testing to ensure that the overall effects will be positive. Introduced without care, innovations can cause damage both to the environment and the people living in it.

19The fact that innovation should be treated with care does not mean that one may now return to the use of earlier technologies unchanged. This is both impossible and undesirable. Modern technologies have made possible some very important improvements in techniques and in approaches. The changes in the social, technical and natural environment in Yemen make a “return to the past” quite impossible: population density has increased, the climate appears to be changing, 'traditional' social relations between landowners and agricultural workers cannot and should not be re-established. Hence technical and social approaches to agricultural development need to be developed that profit from the best in traditional technologies while making use of modern technological innovations insofar as they can be useful. This paper is not a call for a return to the past, promoting a luddite approach to modern technologies, nor is it an appeal for indiscriminate support of modern technologies to the exclusion of traditional ones. We believe that modern equipment and approaches can be used to improve traditional technologies. Similarly, intervention is necessary to ensure that technological change is used to improve social relations rather than exacerbate existing inequities.

Table 1: Comparison of traditional and gabion structures

Item Traditional Structures Gabion Structures
Material availability In wādīs or nearby mountains Imported
Quality of materials Quality stones locally available Good quality gabion is costly
Construction experience Limited to a few local experts Can be learned quickly
Construction cost Reasonable Higher than traditional
Community organizations Strengthened by need to cooperate Weakened by external support
Modern heavy machinery Improve their construction Needed for construction
Damage by heavy floods Low High

© Centre français de recherche de la péninsule Arabique, 2003

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