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Accueil du site → Doctorat → Autriche → Spatial and Temporal Variability of Awash River Water Salinity and the Contribution of Irrigation Water Management in the Development of Soil Salinization Problem in the Awash Valley of Ethiopia

Universitaet fuer Bodenkultur Wien (2002)

Spatial and Temporal Variability of Awash River Water Salinity and the Contribution of Irrigation Water Management in the Development of Soil Salinization Problem in the Awash Valley of Ethiopia

Alamirew Agumassie Tena

Titre : Spatial and Temporal Variability of Awash River Water Salinity and the Contribution of Irrigation Water Management in the Development of Soil Salinization Problem in the Awash Valley of Ethiopia

Auteur : Alamirew Agumassie Tena

Akad. Grad : Thesis.Doctoral 2002

Université de soutenance : Universitaet fuer Bodenkultur Wien ; Institut fuer Hydraulik und landeskulturelle Wasserwirtschaft

Résumé
In order to identify the probable cause of soil salinization problems in the Awash valley, the water quality of the irrigation water source, the Awash River, and aspects of irrigation water management practices in two selected farms were investigated. The water quality appraisal included the spatial and seasonal variability of the river water quality in terms of its salinity and soluble salt composition. The irrigation schedule currently practiced, the depth to the water table, and groundwater electrical conductivity observations at Melka Sedi for the last 20 years were used to evaluate the contribution of irrigation water management practice to the problem. Moreover, soil samples were collected from profiles and analyzed in order to determine the seasonal dynamics of salt in the root zone. Soluble salt speciation and soil physical properties were also evaluated. Different simulation models have been used to determine the suitability of irrigation water, irrigation scheduling, and to evaluate irrigation water management scenarios. A computer program has also been developed to predict the danger of capillary salinization for a given water table depth and set of soil-water characteristic parameters using alternative approaches to the solution. Based on this study and on available guidelines, the Awash River water quality per se couldn’t be regarded as the primary cause of salinization problem in the valley. The salinity of the river water was good during the wet season. It was neither too low (= 0.25 dS m-1) nor too high ( ;0.7 dS m-1) in either season. During the dry season, however, it was closer to the upper threshold value especially downstream of Melka Werer. There were no toxicity problems detected although the balance of sodium to calcium and prevalence of bicarbonate ions require attention for sustainable utilization. The process of soil salinization in the two study sites were found different. In Melka Sedi plains, the problem is irrigation-induced salinization. The application of water in excess of crop water requirement resulted in a deep percolation much higher than the natural lateral drainage. A water table rise of 0.7 to 1.6 m per year has been observed. The rate of rise was faster in the first five years of irrigation development, but it decreased in the next five years stressing the importance of capillary flux once the water table equilibrated within the critical depth. The silty loam soil prevailing in the area was found to be undesirably ideal for capillary salinization. In Abadir farms the cause of soil salinization is saline-sodic water intrusion from Lake Beseka. Irrigation plays no direct role in the process. On the contrary, irrigation helped in containing the severing salinity problem on cultivated fields. The solution to the salinization problem in the Melka Sedi area is water table control, i.e., providing an exit for the deep percolation water. Proper irrigation water management in the area could probably have helped in delaying the onset of problem. With the degree of irrigation efficiency achievable with the furrow irrigation method employed on the farms, irrigation water management may not totally preclude the problem in the long run. The limited natural drainage has been badly constrained by seepage from the river and the main irrigation canal. Hence subsurface drainage can only be achieved with the installation and efficient operation of subsurface drains. For Abadir farms, on the other hand, the first step in the management of salinity problem is to control the water level in Lake Beseka. Afterwards, treating the soil with chemical amendments and careful leaching can do the task of reclaiming the sodium-affected fields on the farm.

Mots clé :
Wasserqualität, Bodensalzgehalt, Bewässerungswirtschaft, bewässerungsinduzierte Bodenversalzung, Äthiopien — Water quality, soil salinity, irrigation water management, secondary salinization, Ethiopia

Présentation : Österreichische Dissertationsdatenbank

Page publiée le 27 mai 2008, mise à jour le 13 mars 2019