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Wageningen Universiteit (2005)

Development and management of irrigated lands in Tigray, Ethiopia

Eyasu Yazew Hagos

Titre : Development and management of irrigated lands in Tigray, Ethiopia

Auteur : Eyasu Yazew .Hagos.

Université de soutenance : Wageningen Universiteit

Grade : Doctor Thesis 2005

Présentation
Ethiopia is a landlocked country in the East of Africa. With the involvement of 90% of the population, agriculture is the major source of employment, revenue and export earnings. The total area of Ethiopia is about 110 million ha of which 67% is arid or semi-arid. With about 90% living in rural areas, the population of Ethiopia has raised from 22 million in 1961 to about 69 million at present with an average annual growth rate of 3%.
Ethiopia is characterised by famine as a result of high population pressure, resource base degradation, and insufficient rainfall for rainfed production. With 22 major drought occurrences in the past 40 years alone, the country generally faces an annual cereal food deficit of 0.03 – 3.3 million tons. On the other hand, it is endowed with a huge annual water resource potential of about 110 billion m3, a potentially irrigable land of 3.6 million ha and productive manpower of about 48% of the total population. However, only about 3 billion m3 of the water resource and 190,000 ha of the potentially irrigable land is utilised so far.
Taking into account the potentials of land and water resources, and the problems of food insecurity, population increase, and limited rainfall, agricultural development has been a priority for the new Ethiopian government since 1991. The Agricultural Development-Led Industrialization (ADLI) development strategy adopted in August 1992 has set irrigation as a major pillar to increase food production and to achieve food self-sufficiency for the country.
With a total land area of 8 million ha, Tigray is one of the most degraded and drought prone regions of Ethiopia. The present population stands at 3.7 million, with an average annual growth rate of 3.3%. The annual cereal food deficit is estimated at about 180,000 tons. There are many causes of the structural food shortage of which moisture deficit plays a significant role. The climate of Tigray is mainly semi-arid and most of the region receives limited and erratic rainfall that is insufficient for crop production. On the other hand, about 9 billion m3 of water leaves the region as runoff annually. For instance, if 50% of this runoff would be used for irrigation, half-a-million hectare of land can be irrigated, which would be sufficient to feed three times the present population of Tigray. The estimated irrigation potential is about 325,000 ha out of which only about 15,000 ha is irrigated through traditional practices.
Realising these problems and potentials, the regional Government has been engaged in earthen dam irrigation development activities for the last few years. The Commission for Sustainable Agriculture and Environmental Rehabilitation in Tigray (CoSAERT) was established in 1994 to construct 500 dams and to irrigate 50,000 ha within ten years. The principal objectives were to change the agrarian system to widespread small-scale irrigated agriculture and to gradually attain self-sufficiency in food production.
So far 44 earthen dams with related irrigation facilities have been constructed and, on average, about 1,418 ha land is annually irrigated. The earthen dam irrigation schemes consist of a catchment area, a reservoir, an earthen dam, and a command area. The command area of most of these schemes is further divided into a primary and a secondary command area. The primary command area is the one irrigated by the proper canal water released from the reservoir through the outlet, while the seepage water from the reservoir through the dam irrigates the secondary command area. The average catchment area, reservoir area, reservoir capacity, dam height, crest length, potential irrigable area and actual irrigated area per dam are 950 ha, 25 ha, 1.1 million m3, 15.5 m, 378 m, 67 ha and 32 ha respectively. There is, however, a considerable variation among individual schemes.
The success of the present and future small-scale irrigation schemes to reduce poverty and gradually ensure food-security in the region depends on their sustainability. The general principle of sustainability is the development, use and management of the land and water resources in such a way that the future generation will not be put at risk. According to Savenije (1997), the major aspects of sustainability are : - environmental sustainability (no long-term negative or irreversible effects) ; - technical sustainability (balanced demand and supply, no mining) ; - economic sustainability (sustaining economic development or welfare and production) ; - financial sustainability (cost recovery) ; - social sustainability (stability of population, stability of demand, willingness to pay) ; - institutional sustainability (capacity to plan, manage and operate the system). _ The focus of the few studies carried out so far in the earthen dam irrigation schemes in Tigray has been on a single component such as reservoir sedimentation and salinity of the irrigated fields. No attempt has been made to study the whole scheme as one integral entity, taking into account the catchment area, the reservoir and dam, and the command area. This research has been initiated and carried out in two earthen dam irrigation schemes, Gumsalasa and Korir, with the main objective of developing an integrated approach for sustainable development and management of irrigated lands in Tigray. The Gumsalasa earthen dam was constructed in 1995 with a reservoir capacity of 1.9 million m3. The Korir earthen dam was constructed a year later with a reservoir capacity of 1.6 million m3. With more than 85% of the total annual rain falling within a period of four months from June to September, rainfall in both sites is unimodal. The average annual rainfall is 513 mm at Gumsalasa and 543 mm at Korir. The dams were constructed by the CoSAERT, while the Bureau of Agriculture and Natural Resources and the farmers carry out the operation and maintenance activities.

Mots clés : IRRIGATED SITES / ETHIOPIA / IRRIGATION / DAMS / RESERVOIRS / WATER MANAGEMENT / SOIL MANAGEMENT / SOIL CONSERVATION / CATCHMENT HYDROLOGY / EROSION

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