The Canals Never Lie

Abstract

The Gezira irrigation scheme, in Sudan, stretches out south of Khartoum between the Blue Nile and the While Nile Rivers. For more than 95 years since its establishment in 1925, the scheme has been a significant asset to Sudan’s economy. It is considered one of the oldest and largest schemes in the world being served by one management body using surface gravity irrigation from a single source. For many years, the system has performed with high efficiency and was considered a good model example, both locally and internationally. In the last few decades the scheme has deteriorated. The water productivity records show declining trends, while more water is being withdrawn from Sennar dam. Farmers are complaining about water shortages and some fields are not reached at all. Authorities state severe damages in the system’s infrastructure, with about 85% of the system’s hydraulic works being damaged. The performance of operation is well below the required efficiency. The sedimentation issue has always been present in the system, especially in the minor canals, but has been severe in recent years. As a result, farmers tend to interfere in the operation of the system, as they are not satisfied with the management authorities. Therefore, the scheme’s operation situations changed accordingly, shifting from the original design approach into new – often undesired – situations. There have been many studies carried in the Gezira Irrigation scheme, in order to understand the reasons behind this deterioration and find sustainable solutions. Starting from the causes of the sedimentation issue and maintenance works, generating new methods of calculating the crop water requirements using remote sensing, influence of farmers’ practices on field level, change of management and institutions throughout the history, and many others. Yet, there is no sensible change seen on the ground. The main objective of this thesis is contribute to the researches done in the Gezira scheme by providing an understanding of how the canalization system’s respond to various water demands strategies. In recent years, there has been a noticeable improvement in methods used to determine crop water requirements using remote sensing. Coping with these improvements, a main question rises, to what extent these remote sensing approaches could be implemented in large irrigation schemes, taking the Gezira scheme as a case study. Determining water requirements is one thing, delivering the water through the canal system could be something else. In order to answer the above question, we first need to analyze the system we are studying. This step was carried through analyzing the current, general, performance of the Gezira scheme and comparing it to the initial design characteristics of the scheme using the MASSCOTE framework (FAO). Using the outcomes of the MASSCOTE evaluation, the thesis proceeded by generating a computer model of the canalization system, taking a major and minor canal as a representation for the water distribution system, and testing different water demands scenarios. This step provided insights into the operation of the canalization system on the level of major and minor canals. It was found that, within the boundaries of our model, implementing new remote sensing methods is practicable, assuming water is readily available at the offtake of the major canal. This conclusion takes into consideration the lengths of the canals and their locations regarding the overall scheme and the carrying capacity of each canals.