Sediments cause serious problems in irrigation systems, adversely affecting canal performance, driving up maintenance costs and, in extreme cases, threatening system sustainability. Multiple studies were done on the deposition of non-cohesive sediment and implications for canal design, the use of canal operation in handling sedimentation problems is relatively under-studied, particularly for cohesive sediments. In this manuscript, several scenarios regarding weirs and gate operation were tested, using the Delft3D model, applied to a case study from the Gezira scheme in Sudan. Findings show that weirs play a modest role in sedimentation patterns, where their location influences their effectiveness. On the contrary, gate operation plays a significant role in sedimentation patterns. Reduced gate openings may cause canal blockage while intermittently fully opening and closing of gates can reduce sediment deposition in the canal by 54% even under conditions of heavy sediment load. Proper location of weirs and proper adjusting of the branch canal’s gate can substantially reduce sedimentation problems while ensuring sufficient water delivery to crops. The use of 2D/3D models provides useful insights into spatial and temporal patterns of deposition and erosion but has challenges related to running time imposing a rather coarse modelling resolution to keep running times acceptable.

Irrigation systems performance and sustainability are affected by sediment deposition. Cohesive sediment (suspended load) is an important problem in irrigation canals and its behaviour is significantly different from that of non‐cohesive sediment (bed load). Most studies on sedimentation in irrigation systems deal with non‐cohesive sediment. Studies on cohesive sediments are mostly done in rivers and estuaries, but not in irrigation canals. The few existing studies on cohesive sediment in irrigation canals are limited by their use of 1D models. Therefore, in this study we test whether an existing 3D model that was designed for rivers and estuaries can be used in irrigation canals. Delft3D was identified as a suitable model. Simulations were done for different sizes and configurations of the irrigation network. After some adaptations to the model, the simulations of different scenarios provided promising results. From a hydrodynamic and morphological point of view the Delft3D model was able to realistically represent water and sediment flows in a hypothetical canal set‐up, consisting of a main canal, a branch canal and several hydraulic structures. Some challenges remain in the use of Delft3D for irrigation canals, in particular regarding wall roughness in small rectangular canals and computation times for complex systems. However, these challenges are not insurmountable and the advantages of using Delft3D are clearly shown in this paper. © 2019 John Wiley & Sons, Ltd.

In order to cover the crop water requirements, flow control structures such as gates and weirs are used to transfer the desired amount of water from the canals to the field canals. This paper examines the impact of gate operation and the selection of gates on the deposition of non-cohesive sediment. The Delft3D model is used to simulate the effects of different scenarios regarding gate operation and the location of the gate that is opened. The model results showed that the gate selection affects not only hydraulic parameters but also morphological parameters. It was found that opening the gates closer to the offtake resulted in less sediment deposition at the entrance of the branch canal when compared to opening the gates further away. Gate selection can be used as a tool in sediment management. By alternating the opening of different gates sediments that are already deposited after opening one gate can be eroded when another gate is operated, thus minimizing the additional cost of sediment removal. The use of Delft3D proved beneficial as the selection of different gates leads to asymmetric sediment deposition patterns which would be missed when using a 1D model.

There are many people who were involved and gave lots of assistance and cooperation in this research. The author would like to deliver the gratefulness for their contribution.Firstly, I would like to thank my Promoter and supervisor, Prof. Charlotte de Fraiture PhD, MSc who gave opportunity, ideas and support to this study, also I would like to thank Dr. Bert Jagers from Deltares for always sharing the ideas, knowledge and encouragement, the technical support and guiding me during this research and for his kind brotherly support. Also many thanks to my co-promotor Dr. F.X. Suryadi, PhD, MSc for sharing the ideas and guiding during my research. I would like to thanks would like to thank the Iraqi Ministry of Higher Education and ScientificResearch and the Ministry of Water Resources as well for funding my scholarship. Additionally, I would like to thank Deltares in Delft, the Netherlands for their technical support in providing the new version of the Delft3D and all modelling courses and workshops, it really appreciated especially Bert Jagers and Edward Melger. I also express my gratitude for other staff of Hydraulic Engineering -Land and Water Development, I also express my gratitude for other staff of Hydraulic Engineering in Wageningen University and all guest lecturers who have taught me during my study in IHE-Delft.Thanks to all my family of IHE who shared time together and did support each other and I would like to thank Prof. Bart Schultz, PhD, MSc for his help from the beginning, and my best friends Marielle Van Ervan, Mireia Lopez Royo, Zaki Shubber and Tonneke Morgenstond for their kind support. Many thanks to Professor Dano Roelvink, Roel Noorman, Loes Westerveen, Gordon de Wit, Jaap Kleijn and Lennard Teileman for their brotherly help. I would show their appreciation Dr. K.P. Paudel and SMIS for their field data and reports that have other data helpful for this study. Above all, I would like to express my gratefulness for my husband Naser A. Kadhim and my son Ali, I dedicate this thesis as an insignificant gift for your endless love and sacrifices. Finally yet importantly, for others who were not mentioned but contributed to this thesis, I express my gratitude.

There are many people who were involved and gave lots of assistance and cooperation in this research. The author would like to deliver the gratefulness for their contribution. Firstly, I would like to thank my Promoter and supervisor, Prof. Charlotte de Fraiture PhD, MSc who gave opportunity, ideas and support to this study, also I would like to thank Dr. Bert Jagers from Deltares for always sharing the ideas, knowledge and encouragement, the technical support and guiding me during this research and for his kind brotherly support. Also many thanks to my co-promotor Dr. F.X. Suryadi, PhD, MSc for sharing the ideas and guiding during my research. I would like to thanks would like to thank the Iraqi Ministry of Higher Education and Scientific Research and the Ministry of Water Resources as well for funding my scholarship. Additionally, I would like to thank Deltares in Delft, the Netherlands for their technical support in providing the new version of the Delft3D and all modelling courses and workshops, it really appreciated especially Bert Jagers and Edward Melger. I also express my gratitude for other staff of Hydraulic Engineering-Land and Water Development, I also express my gratitude for other staff of Hydraulic Engineering in Wageningen University and all guest lecturers who have taught me during my study in IHE-Delft. Thanks to all my family of IHE who shared time together and did support each other and I would like to thank Prof. Bart Schultz, PhD, MSc for his help from the beginning, and my best friends Marielle Van Ervan, Mireia Lopez Royo, Zaki Shubber and Tonneke Morgenstond for their kind support. Many thanks to Professor Dano Roelvink, Roel Noorman, Loes Westerveen, Gordon de Wit, Jaap Kleijn and Lennard Teileman for their brotherly help. I would show their appreciation Dr. K.P. Paudel and SMIS for their field data and reports that have other data helpful for this study. Above all, I would like to express my gratefulness for my husband Naser A. Kadhim and my son Ali, I dedicate this thesis as an insignificant gift for your endless love and sacrifices. Finally yet importantly, for others who were not mentioned but contributed to this thesis, I express my gratitude.