Sediment deposition threatens the performance of many irrigation systems. Because of the high impact on irrigation performance and crop production, many studies have been done on how to deal with sediment deposition. In this research, the Delft3D model, originally developed for hydro-morphologic modeling of rivers and estuaries, was adapted for the use in irrigation systems simulations and applied to different case studies. This research addresses two shortcomings of previous studies of sediments in irrigation systems. Firstly, while previous studies primarily used 1D models, this research uses a 2D/3D model. The use of 2D/3D models in irrigation systems is significant because the non-uniform flow around structures such as offtakes, weirs and gates, leads to asymmetric sedimentation patterns that are missed by 1D simulations. Secondly, whereas previous studies mostly considered non-cohesive sediments, this research simulates cohesive, non-cohesive and a mix of both sediment types. This is important for irrigation systems that draw water from natural rivers that carry a mix of cohesive and non-cohesive sediments. The findings of this research are important for irrigation system maintenance and gate operation. It is also essential for the development of canal operating plans that meet crop water requirements and at the same time minimizes sediment deposition by alternating gates.

After publishing the famous “Fluvial Processes in Geomorphology” in the early 1960s, the work of Luna Leopold, Gordon Wolman, and John Miller became a key for opening the door to understanding rivers and streams. They first illustrated the problem to geomorphologists and geographers. Later, Chang, in his “Fluvial Processes in River Engineering”, provided a basis for engineers, showing this group of professionals how to deal with rivers and how to understand them. Since then, more informative studies have been published. Many of the authors started to combine fluvial geomorphology knowledge and river engineering needs, such as “Tools in Fluvial Geomorphology” by G. Mathias Kondolf and Hervé Piégay, or focused more on river engineering tasks, such as “Stream Restoration in Dynamic Fluvial Systems: Scientific Approaches” by Andrew Simon, Sean Bennett, and Janine Castro. Finally, Luna Leopold summarized river and stream morphologies in the beautiful “A view of the river”. It appears that we continue to explore this subject in the right direction. We better understand rivers and streams, and as engineers and fluvial geomorphologists, we can establish tools to help bring rivers alive. However, there is still a hunger for more scientific tools that we could use to further understand rivers and to support the development of healthy streams and rivers with high biodiversity in the present world, which has started to face water scarcity.

The governing physical process of sediment transport can be represented in a scale model without the simplifying assumptions required in numerical modeling. However, the current methods utilized in scaling sediment transport in unsteady open-channel flow result in a number of model and scale effects, which decrease the accuracy and application of scale models. Commonly, researchers apply Froude similitude, vertical distortion by scaling channel width and depth differently, and scaled sediment density to sediment transport models. These practices result in: bank inclination angles which are not conserved, errors in secondary current representation in the model, velocity distortion, inaccurate representation in the location and extent of erosion and deposition, inaccurate bed-porosity, inaccurate description of incipient motion, and dissimilar suspended sediment concentration. A number of criteria for sediment transport scaling are available that aim to decrease the error that results from scaling flow and sediment transport processes. These criteria often solve one issue of similitude in scale models, while simultaneously decreasing similitude of another flow or sediment transport parameter. For example, the scaling of sediment density is a common solution when scaling of the sediment diameter alone would result in cohesive sediments with fundamentally different behavior from non-cohesive sediment. Scaling of the sediment density may increase the similitude of the particle Reynolds number. However, the lighter sediments cause an over-estimation of suspended sediment concentration, and an accelerated time scale for bed deformation. The implications of these errors are not trivial in light of the goal of physical scale modeling to represent prototype conditions accurately enough to use scale models as tools for design and performance prediction, and environmental impact assessment.I propose the use of the one-parameter Lie group of point scaling transformations as a method of scaling sediment transport without the errors encountered in traditional scaling methods. The conditions under which the governing equation for non-equilibrium sediment transport in unsteady flows is self-similar are examined by applying the one-parameter Lie group of point scaling transformations. The conditions are further examined to determine the case in which the sediment material properties need not be scaled. It is proposed that channel depth and width be scaled equally, and the scaling ratio of channel length should equal the square of the scaling ratio of channel depth. The proposed method is compared to the traditional method of vertically distorted Froude similitude and sediment transport scaling. It is shown that under Lie group scaling, the unsteady suspended sediment transport process as an initial- boundary value problem in the prototype domain, can be self-similar with that of a variety of different scaled domains. The scaled values of flow and sediment variables at specified temporal and spatial locations can then be upscaled to the corresponding values in the prototype domain with little to no scale effect. When the geometric scaling is set as I propose, not only are sediment diameter and density unscaled, but so too are the critical and total shear, kinematic viscosity and particle Reynolds number. The similarity of sediment transport is increased through more accurate representation of incipient motion, the time-rate of change of bed morphology, bed porosity, suspended sediment concentration and carrying capacity of flow. The proposed method, detailed herein, meets the needs of modelers by maintaining the benefits found from distortion such as reduced cost, space and model run-time, while simultaneously avoiding the scale effects and resulting errors of traditional flow and sediment transport scaling.

This study focuses on sediment transport in irrigation canals which may have a serious impact on design, operation and maintenance activities. Using a mathematical model, and examing ways in which this model can be applied to real-world situations, this text is highly useful for theoreticians and students alike.