Numerical Simulation Of Hydraulic And Morphologic Changes In Alluvial Channels

With advances in computer technology, the use of river sediment numerical models in calculation of flow, sediment transport, and in prediction of morphological changes in alluvial streams has become increasingly important and popular for river engineering. Many ID and 2D models have been developed and contributed to the hydraulic research in both the laboratories and field as an effective tool for engineering analysis and design. In this study, three different numerical models were used to simulate morphodynamics processes in alluvial channels, depending on which objective is intended.A ID numerical model is developed to simulate degradation and armoring process in alluvial channels. The model calculates the bed variations with the time and space, taking into account the effect of non-uniformity of bed materials, and variation in dimension of bed form. The procedure allows for the estimation of changes in grain size distribution during each time step. The proposed model was applied and compared with experimental data. The numerical results agree well with the observed values.The Second part of the study deal with the application of Generalized Stream Tube model for Alluvial River Simulation GSTARS2.1.to simulate degradation and armoring condition in a reach from a Tigris River downstream of Mosul Dam. The model was verified by using experimental data. Application of the model on Tigris River shows that rate of degradation and armoring is little in the studied reach. The rate of degradation along the reach ranged between 0.5m near the dam and 0.1 m at Mosul city; this means that the Tigris River may have previously reached armoring condition before Mosul dam closure.The third part of the study contains the application of depth-integrated two-dimensional hydrodynamic and sediment transport model CCHE2D, for studying channel flow and morphologic changes in alluvial streams. The model was used for two cases: First to study the effect of channel curvature and transverse bed slope on hydraulic and morphologic characteristics in alluvial channels, under different flow conditions. Second to simulate the flow conditions for a reach from the Ganjiang river in order to determine the characteristics of the flow after building Shengmi bridge at Nanchang city, to establish the navigation feasibility at this section form the river, after the existence of the suggested bridge.It was found from the obtained results that in curved channels there are noticeable difference in water surface profile between outer and inner bank, and this difference increases with increase in flow rate, channel curvature, and transverse bed slope towardinner bank. In channels with transverse bed slope toward inner bank the velocity values at the outer bank are higher than that at inner bank, and this difference increases with increasing in transverse bed slope toward inner bank, while in curved channels without transverse bed slope the velocity values at the inner bank are more than that at outer bank till to middle of the channel curvature there after the velocity at outer bank will start to increase, at the end of the curvature the velocity at the outer bank will be more than that at inner.Bed topographic results show that in 180 curved channels with transverse bed slope there is deposition at outer bank along the reach and erosion at inner bank side from the beginning of the channel till to middle of the reach, there after there is deposition, but when the channel has zero degree transverse bed slope the channel was under erosion condition from the channel entrance till to middle of the channel curvature, after this there is a noticeable deposition at inner bank side. In 90?curved channels there is erosion from channel beginning till to middle of the reach after that there is significant deposition at inner bank side. In straight channels, the bed is almost under erosion condition, and the rate of the erosion is more than as it is in curved channels. The rate of the erosion and deposition in these channels increases with increasing in flow rate, and tr...