Modelling the impact of large impoundments on the Lower Zambezi River

The Lower Zambezi River is influenced by the presence of two very large hydropower impoundments which have modified the natural seasonal flows, the sediment balance, the morphology of the river and the pattern of the riparian vegetation. Downstream of these large impoundments, appreciable local effects are reported to take place, such as scour, bank collapse and shoreline degradation. In order to quantify the sediment transport along the Lower Zambezi River and to predict the effects of the dams on morphology we have developed a simplified 1-D hydro-morphodynamic model capable to deal with the scarcity of available data. Besides the systematic flow records at the dam gauging station and few occasional measurements of turbidity and grain size of the river bed, only the Digital Elevation Model (DEM) and some recent satellite images of the river have been used as the input data of the model. The results confirm the expected qualitative response of the river to the constructions of dams: the reduction of water flow has an immediate effect downstream of the reservoirs by initially fostering the sediment deposition; afterwards, the total interception of sediment by the dams slowly takes over and inverts this tendency; a smaller aggradation rate with respect to the natural conditions without dams, seems to represent the dominant effect of damming in the long-term evolution of the river. The morphological effects of damming over the transversal cross-section of the river have been studied by a simplified transversal quasi 2-D sub-model, coupled to a 1-D longitudinal model. Besides the evolution of the bottom longitudinal profile and grain size composition, the model simulates also the evolution of the cross-section shape and the growth of the riparian vegetation. A first application confirms the qualitative observations reported in the literature on the recent planimetric evolution of the Lower Zambezi. © 2013 Copyright International Association for Hydro-Environment Engineering and Research

Development of a preliminary media wear measurement test procedure for cement ball milling applications

The paper initially focusses on developing a test procedure for measuring the wear of grinding balls and then correlating the results with the wear obtained in industrial scale cement ball milling applications. The cost of grinding media is one of the major items and it needs to be optimized by testing different types of media. Since industrial scale trials are time consuming, there is a need for an easy, accurate and fast media wear testing procedure for cement ball milling applications. Such a procedure enables cement plants to compare wear results of different types of media and choose the optimal one for the economy of the grinding operation. Within the scope of the study, 6 types of 30 mm media having different chemical compositions were subjected to wear measurements at different time intervals by utilizing laboratory scale ball mills. The studies showed that reproducible results can be obtained from the test apparatus hence the methodology is said to be consistent. The wear results concluded that the order of the media wear from the highest to the lowest was the same independent of the mill dimension and whether the material is inside the mill. The results also implied that the chemical composition or the microstructure of the media was an influencing parameter on the wear therefore there is room for improvement with regards to the quality of media. This study proved that the media wear measured at industrial scale cement ball mills was in good agreement with the laboratory scale results. (C) 2017 Elsevier B.V. All rights reserved