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Theories of soil mechanics and basic hydraulic relations and principles of loose boundary channel hydraulics were combined and integrated to analyze stratified river bank failure due to undercutting (undermining) of a bottom loose layer. A near bank velocity distribution model was developed from which the boundary shear stress acting on the bank surface was determined. The model allows computation of the eroded soil volume from the bottom loose layer and the lateral undercut distance at any time in the flow hydrograph as long as the induced flow shear stress is greater than the particle critical shear stress resistance to hydraulic entrainment. At failure the size of the failure block and the ultimate critical value of the lateral undercut distance are determined. Therefore the annual rate of bank retreat and bank sediment load contribution can be identified for the reach under consideration. The application of the model to the River Nile hydrograph in Northern Sudan State showed a good agreement with field observations.

In this paper methods for determination of maximum local scour depth and eroded material volume downstream of highway drainage structures were developed. Severe local scour leads to undermining followed by collapsing of the drainage structure. The analysis method is based on integrating a new technique of improved drainage structure outlet geometry, jet hydraulic characteristics and soil properties. The jet velocity, induced shear stress, critical shear resistance to erosion and particle size are the main factors that control the erosion process downstream of a drainage structure. The study is of experimental and theoretical nature. The developed mathematical model was calibrated using collected field data in addition to laboratory tests. The produced scour holes were plotted for each laboratory run and the scour hole depth, width and length were measured. A semi- empirical relation has been developed for predicting the depth of local scour hole. It is based on Densimetric Froude number. It is found that the semicircular apron gives less scour depth and width when compared to the linear front apron. The comparison of the model outputs and field study is found of a good agreement. The model is recommended for engineering design of highway drainage structures located on streams of sandy bed.

Sediment and water management are key issues in irrigation schemes that suffer from accumulation of sediment along canals. This accumulation creates problems with adequate water supply and may lead to water shortage. The aim of this study was to analyse improvement options for operation and maintenance in order to achieve better sediment and water management in irrigation canals. A model has been developed to simulate cohesive sediment transport in irrigation canals. The model is a useful tool to predict cohesive sediment deposition under different operation and maintenance scenarios. It has been calibrated and validated by using field data of the Gezira Scheme in Sudan and has been applied for different options of operation. The best operation scenario was found when the scheme was operated based on the crop water requirement during the period of high sediment concentration. When the inflow was reduced by 51% during this period in 2011, the reduction in deposition was 48%. Such types of adaptation will significantly reduce deposition and improve sediment and water management in irrigation canals. Copyright © 2016 John Wiley & Sons, Ltd.

Most of the models developed to simulate the cohesive sediment transport processes refer to estuary or marine environments and are generally not developed for the specific characteristics of irrigation schemes provided with the different types of hydraulic structures. The aim of this study is to simulate the cohesive sediment transport in irrigation canals. The fine sediment transport (FSEDT) model was developed using a software program to estimate the sediment transport and deposition rates of cohesive sediments in irrigation canals. The model has been applied in the Gezira Scheme in Sudan, which is threatened by high sediment supply from the Blue Nile River. The model was calibrated and validated using the field data selected during the flood seasons in 2011 and 2012. The hydrodynamic part of the model was verified by comparing the water surface profile obtained by the developed model and by using a microcomputer program for simulating one-dimensional steady/unsteady flow in open canals. The res...