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University of Gezira (2017)

Assessment of the Irrigation Water Supply from Minor Canal to Field Ditches in the Gezira Scheme : A Case Study of Toman Minor, Sudan

Fadl El Mola, Khalid Mohamed Haj Elneel

Titre : Assessment of the Irrigation Water Supply from Minor Canal to Field Ditches in the Gezira Scheme : A Case Study of Toman Minor, Sudan

Auteur : Fadl El Mola, Khalid Mohamed Haj Elneel

Université de soutenance : University of Gezira

Grade : Master of Science (MS) in Water Management 2017

Résumé
Irrigation sustains the agricultural production in Sudan. Gezira scheme (0.88 million ha) is the largest irrigation scheme in the world under a single administration. The scheme has been established since 1925 as a single crop rotation. In 1970s, the diversification and intensification policy has been adopted, during which the cropping intensity has tremendously increased. The main grown crops are cotton, sorghum, groundnut and wheat. The irrigation network is a gravity-fed system. Its economic performance however showed a decreasing trend in the recent years. This largely attributed to the irrigation water mismanagement. The general objective of this study is to determine and explain the water distribution in the irrigation system during the peak irrigation period at minor canal and field ditches. The specific objectives were to assessing the performance of minor canal and the on-farm ditches in Toman minor of six km in length and command area of 1915 feddan. Fieldwork and desktop datasets were being collected. The collection of field datasets (discharge, water level, sediment concentrations, canal dimensions, etc) extended for six weeks (September-October 2011). The collected datasets processed and analyzed using the Sobek software. The Study applied, for the first time in the Gezira scheme, the dilution gauging with a sudden gulp injection of salt method for measuring the discharge. The total water requirements for the Toman command area is determined based on the sowing dates, Penman evaporation and crop factors. The results showed that the Toman minor canal experienced elevated bed levels, averaged in 0.73 m higher than the design bed level due to sediment accumulation. The average silt concentration at the Toman off-take was found to be 0.7 kg/m3, which is almost 8% of the peak concentration in the Blue Nile. The actual water release exceeds the crop water requirements by a factor of 2.5, excluding the pre-irrigation events. However, the actual release of Abu XX was not exceeded 3000 m3day-1, which is below than the design one of 5000 m3/day. The study recommends the revisiting of the current methods of water computations in the Gezira scheme as well as that, the crop rotation should be abided to the canal capacity.

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